Chemistry Exam 2
Based on the activity series, which one of the reactions below will occur?
Mn(s) + NiCl2(aq) → MnCl2(aq) + Ni(s)
the total number of atoms in 0.111 mol of Fe(CO)3(PH3)2 is
1.00 x 10^24
a typical neutralization titration - between a
HCl solution of unknown concentration and a NaOH solution
moles provide a bridge from the molecular scale to the
real world scale
how many moles of pyridine (C5H5N) are contained in 3.13g of pyridine?
0.0396
What are the respective concentrations (M) of K+ and PO4 3- afforded by dissolving 0.800 mol K3P O4 in water and diluting to 1.63 L?
1.44 and 0.491
one can find the percentage of the mass of a compound that comes from each of the elements in the compound by using this equation:
% element = (# of atoms)(atomic weight) / (fw of the compound) x 100
What is the concentration (M) of CH3OH in a solution prepared by dissolving 11.7 g of CH3OH in sufficient water to give exactly 230. mL of solution?
1.59
Aqueous solutions of a compound did not form precipitates with Cl-, Br-, I-, SO4 2-, CO32-, P O4 3-, OH-, or S2-. This highly water-soluble compound produced the foul-smelling gas H2S when the solution was acidified. This compound is __________.
(NH4)2S
gaining "chemical intuition" - understanding how to categorize a rxn
- try to recognize patterns to determine the general category of a rxn, such as metathesis or red-ox - when you are faced with the challenge of predicting the outcome of a chemical rxn, ask yourself the following questions: - what are the reactants in the rxn? - are they electrolytes or nonelectrolytes? - are they acids or bases? - if the reactants are electrolytes, will metathesis produce a precipitate? water? a gas? - if metathesis cannot occur, can the reactants possibly engage in a red-ox rxn?
nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions. Flourine always has an oxidation number of
-1. the other halogens have an oxidation number of -1 when they are in compounds of type AX, where x= halogen they can have positive oxidation numbers, however, most notably in oxyanions - XOn-
the sum of the oxidation numbers in a neutral compound is
0. the sum of the oxidation numbers in a polyatomic ion is the charge on the ion.
A 31.5 mL aliquot of H2SO4 (aq) of unknown concentration was titrated with 0.0134 M NaOH (aq). It took 23.9 mL of the base to reach the endpoint of the titration. The concentration (M) of the acid was __________.
0.00508
to convert moles to formula units, we need avogadros number how many glucose molecules are in 0.029 moles of C6H12O6?
0.029 moles x (6.02 x 10^23 molecules C6H12O6/ 1 mol C6H12O6) = 1.75 x 10^22 molecules of C6H12O6
how many oxygen atoms are in 0.029 moles of C6H12O6?
0.029 moles x (6.02 x 10^23 molecules C6H12O6/ 1 mol C6H12O6) = 1.75 x 10^22 molecules of C6H12O6 atoms O= (1.75 x 10^22 molecules C6H12O6)(6 atoms O/ 1 molecule C6H12O6) = 1.05 x 10^23 atoms O
An aliquot (28.7 mL) of a KOH solution required 31.3 mL of 0.118 M HCl for neutralization. What mass (g) of KOH was in the original sample?
0.207
Which one of the following solutions will have the greatest concentration of hydroxide ions?
0.300 M rubidium hydroxide
What mass (g) of CaF2 is formed when 47.8 mL of 0.334 M NaF is treated with an excess of aqueous calcium nitrate?
0.623
A solution is prepared by adding 1.60 g of solid NaCl to 50.0 mL of 0.100 M CaCl2. What is the molarity of chloride ion in the final solution? Assume that the volume of the final solution is 50.0 mL
0.747
How many moles of Na+ are present in 343 mL of a 1.27 M solution of Na2SO4?
0.871
the strong bases are the soluble metal salts of hydroxide ion (4)
1. alkali metals 2. calcium 3. strontium 4. barium
the study of stoichiometry provides an essential set of tools that is widely used in chemistry. stoichiometry is build on an understanding of (3)
1. atomic masses 2. chemical formulas 3. the law of conservation of mass
rxn types (5)
1. combination rxns 2. combustion (oxidation) rxn 3. decomposition rxns 4. metathesis rxns - neutralization rxns - precipitation rxns - gas forming rxns 5. oxidation-reduction rxns
there are only 7 strong acids:
1. hydrochloric (HC) 2. Hydrobromic (HBr) 3. Hydroiodic (HI) 4. Nitric (HNO3) 5. Sulfuric (H2SO4) 6. Chloric (HClO3) 7. Perchloric (HClO4)
ascorbic acid (vitamin c) contains 40.92% C, 4.58% H, and 54.50% O by mass. what is the empirical formula of ascorbic acid?
1. we assume we have exactly 100g of material (although any other mass could also be used) in 100g of ascorbic acid, we have 40.92g C, 4.58g H, 54.50g O. 2. we calculate the number of moles of each element i.e moles of C = (40.92g C) (1 mol C/12.01 g C) = 3.407 mol C 3. we determine the simplest whole number ration of moles by dividing each number of moles by the smallest number of moles (in other words, after we find the moles of H, C and O, we divide each by the smallest value because we need the simplest whole number ratio of moles by dividing each number of moles by the smallest number) the ratio for H is too far from 1 to attribute to the difference to experimental error. we should multiply the rations by 3 to obtain whole numbers. C:H:O = 3(1:1.33:1) = 3:4:3 the empirical formula is C3H4O3 (you find the smallest number that multiplies by 1.33. Each subscript is multiplied by 3, to keep the ratios. because remember that the ratios give the identity of the compound)
steps of writing net ionic equations
1. write a balanced equation 2. dissociate all strong electrolytes 3. cross out anything that remains unchanged from the left side to the right side of the equation 4. write the net ionic equation with the species that remain
What is the maximum amount in grams of SO3 that can be produced by the reaction of 1.0 g of S with 1.0 g of O2 via the equation below? S (s) + O2 (g) → SO3 (g) (not balanced)
1.7
one million argon atoms is ___ mol (rounded to two significant figures) of argon atoms
1.7 x 10^-18
how many molecules of CH4 are in 48.2g of this compound?
1.81 x 10^24
Which of the following would require the largest volume of 0.100 M sodium hydroxide solution for neutralization?
10.0 mL of 0.0500 M phosphoric acid
which is more concentrated, a solution prepared by dissolving 21.0 g of NaF (0.500 mol) in enough water to make 500 mL of a solution or a solution prepared by dissolving 10.5g (0.250 mol) of NaF in enough water to make 100 mL of solution?
10.5g of NaF dissolved in water to make 100mL of solution
there are ___ hydrogen atoms in 25 molecules of C4H4S2
100
Which solution has the same number of moles of NaOH as 50.00 mL of 0.100M solution of NaOH?
100.00 mL of 0.0500M solution of NaOH
What volume (mL) of a concentrated solution of magnesium chloride (9.00 M) must be diluted to 350. mL to make a 2.75 M solution of magnesium chloride?
107
The combustion of ammonia in the presence of oxygen yields NO2 and H2O: 4 NH3 (g) + 7 O2 (g) → 4 NO2 (g) + 6 H2O (g) The combustion of 43.9 g of ammonia with 258 g of oxygen produces __________ g of NO2.
119
the combustion of ammonia in the presence of excess oxygen yields NO2 and H2O: 4NH3(g) + 7O2(g) -> 4NO2(g) + 6H2O (g) the combustion of 43.9 g of ammonia produces ___g of NO2
119g
Pentacarbonyliron (Fe(CO)5) reacts with phosphorous trifluoride (PF3) and hydrogen, releasing carbon monoxide: Fe(CO)5 + PF3 + H2 → Fe(CO)2(PF3)2(H)2 + CO (not balanced) The reaction of 5.0 mol of Fe(CO)5, 8.0 mol of PF3 and 6.0 mol of H2 will release __________ mol of CO.
12
What volume (mL) of 7.48 × 10-2 M phosphoric acid can be neutralized with 115 mL of 0.244 M sodium hydroxide?
125
What volume (ml) of a 3.45 M lead nitrate solution must be diluted to 450.0 ml to make a 0.990 M solution of lead nitrate?
129
if O2 had been the limiting reactant, how many moles of H2O would have formed?
14 mol H2O
under the appropriate conditions, nitrogen and hydrogen undergo a combination rxn to yield ammonia: N2(g) + 3H2(g) -> 2NH3(g) a ___g sample of N2 requires 3.0g of H2 for complete rxn
14.0g
a gross is a grouping that consists of
144 items in a gross
In which reaction does the oxidation number of hydrogen change?
2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g)
How many grams of NaOH (MW = 40.0) are there in 250.0 mL of a 0.275 M NaOH solution?
2.75
how many moles of sodium carbonate contain 1.773 x 10^17 carbon atoms?
2.945 x 10^-7
a score is a grouping that consists of
20 items in a set group
How many milliliters of a stock solution of 11.1 M HNO3 would be needed to prepare 0.500 L of 0.500 M HNO3?
22.5
the molecular formula of aspartame, the generic namefor NutraSweet, is C14H18N2O5. the molar mass of aspartame, rounded to the nearest integer, is ___g
294g
Of the reactions below, only __________ is not spontaneous.
2Ag(s) + 2HNO3(aq) → 2AgNO3(aq) + H2(g)
The balanced reaction between aqueous nitric acid and aqueous strontium hydroxide is __________.
2HNO3(aq) + Sr(OH)2(aq) → 2H2O(l) + Sr(NO3)2(aq)
the structural formula of citric acid, a main component of citrus fruit is C6H8O7. how many H+(aq) can be generated by each citric acid molecule dissolved in water?
3
write the balanced equation for the rxn that occurs when methanol, CH3OH(l) is burned in air. what is the coefficient of oxygen in the balanced equation?
3
how many atoms of Mg, O, and H are represented by the notation 3Mg(OH)2?
3 Mg, 6O ad 6H
Silver nitrate and aluminum chloride react with each other by exchanging anions: 3AgNO3 (aq)+ AlCl3 (aq) → Al(NO3)3 (aq) + 3AgCl (s) What mass in grams of AgCl is produced when 4.22 g of AgNO3 react with 7.73 g of AlCl3?
3.56
calcium carbide (CaC2) reacts with water to produce acetylene (C2H2): CaC2(s) + 2H2O(g) -> Ca(OH)2(s) + C2H2(g) the complete rxn of 57.4g of CaC2 requires consumption of ___g of H2O
32.3g
Lead ions can be precipitated from aqueous solutions by the addition of aqueous iodide: Pb2+(aq) + 2I-(aq) → PbI2(s) Lead iodide is virtually insoluble in water so that the reaction appears to go to completion. How many milliliters of 3.550 M HI(aq) must be added to a solution containing 0.700 mol of Pb(NO3) 2 (aq) to completely precipitate the lead?
394
a sample of CH2F2 with a mass of 19g contains ___ atoms of F
4.4 x 10^23
What are the respective concentrations (M) of Mg+2 and C2H3O2- afforded by dissolving 0.600 mol Mg(C2H3O2)2 in water and diluting to 135 mL?
4.44 and 8.89
Oxalic acid is a diprotic acid. Calculate the percent of oxalic acid (H2C2O4) in a solid given that a 0.7984-g sample of that solid required 37.98 mL of 0.2283 M NaOH for neutralization
48.89
The molarity (M) of an aqueous solution containing 52.5 g of sucrose (C12H22O11) in 35.5 mL of solution is __________.
5.46
propane (C3H8) reacts with oxygen in the air to produce carbon dioxide and water. in a particular experiment, 38.0g of carbon dioxide are produced from the exn of 22.05g of propane with excess oxygen. what is the % yield of this rxn?
57.6
what is the molar mass of glucose C6H12O6?
6 C atoms = 6(12.0 amu) = 72.0 amu 12 H atoms = 12(1.0 amu) = 12.0 amu 6 O atoms = 6(16.0 amu) = 96.0 amu = 180.0 amu glucose has a formula weight of 180.0 amu 1 mol of this substance (6.02 x 10^23 molecules) has a mass of 180.0g. C6H12O6 has a molar mass of 180.0 g/mol
Lead (II) carbonate decomposes to give lead (II) oxide and carbon dioxide: PbCO3 (s) → PbO (s) + CO2 (g) __________ grams of lead (II) oxide will be produced by the decomposition of 7.50 g of lead (II) carbonate?
6.26
GeF3H is formed from GeH4 and GeF4 in the combination rxn: GeH4 + GeF4 -> 4GeF3H if the rxn yield is 92.6% how many moles of GeF4 are needed to produce 8.00 mol of GeF3H?
6.48
How many grams of sodium chloride are there in 550.0 mL of a 1.90 M aqueous solution of sodium chloride?
61.1
In a titration of 35.00 mL of 0.737 M H2SO4, __________ mL of a 0.827 M KOH solution is required for neutralization
62.4
A 13.8 mL aliquot of 0.176 M H3PO4(aq) is to be titrated with 0.110 M NaOH(aq). What volume(mL) of base will it take to reach the equivalence point?
66.2
Which solution contains the largest number of moles of chloride ions?
7.50 mL of 0.500M FeCl3
Sulfur and fluorine react in a combination reaction to produce sulfur hexafluoride: S (s) + 3F2 (g) → SF6 (g) In a particular experiment, the percent yield is 79.0%. This means that in this experiment, a 7.90 -g sample of fluorine yields __________ g of SF6.
7.99
Calcium oxide reacts with water in a combination reaction to produce calcium hydroxide: CaO (s) + H2O (l) → Ca(OH)2 (s) In a particular experiment, a 1.50-g sample of CaO is reacted with excess water and 1.48 g of Ca(OH)2 is recovered. What is the percent yield in this experiment?
74.8
Which combination will produce a precipitate?
Pb(NO3)2 (aq) and HCl (aq)
oxidation of metals by acids and salts (3 formula rxn examples)
A + BX -> AX + B Zn(s) + 2HBr(aq) -> ZnBr2(aq) + H2(g) Mn(s) + Pb(NO3)2(aq) -> Mn(NO3)2(aq) + Pb(s)
what do the following abbreviations stand for? AW FW MW
AW - atomic weight - atoms FW - formula weight - ionic compounds MW - molecular weight - molecules
When aqueous solutions of AgNO3 and KI are mixed, AgI precipitates. The balanced net ionic equation is __________.
Ag+ (aq) + I- (aq) → AgI (s)
the balanced equation lists the reactants and products in their molecular or formula unit form
AgNO3(aq) + KCl(aq) -> AgCl(s) + KNO3(aq)
metathesis comes from a greek word that means "to transpose". it appears that the ions in the reactant compounds exchange, or transpose, ions.
AgNO3(aq) + KCl(aq) -> AgCl(s) + KNO3(aq) AX + KY -> AY + KX
why isnt Al(OH)3 classified as a strong base?
Al(OH)3 is insoluble in water
The net ionic equation for formation of an aqueous solution of Al(NO3)3 via mixing solid Al(OH)3 and aqueous nitric acid is __________.
Al(OH)3(s) + 3H+(aq) → 3H2O(l) + Al3+ (aq)
Of the species below, only __________ is not an electrolyte
Ar
which hydrocarbon pair below have identical mass percentage of C?
C2H4 and C3H6
a compound contains 40.0% C, 6.71% H and 53.29% O by mass. the molecular weight of the compound is 60.05 amu. the molecular formula of this compound is
C2H4O2
a compound is composed of only C, H, and O. the combustion of a 0.519g sample of the compound yields 1.24g of CO2 and 0.255g of H2O. what is the empirical formula of the compound?
C3H3O
consider solutions in which 0.1 mol of each of the following compounds is dissolved in 1L of water: Ca(NO3)2 (calcium nitrate), C6H12O6 (glucose), NaCH3COO (sodium acetate) and CH3COOH (acetic acid) rank the solutions in order of increasing electrical conductivity, based on the fact that the greater the number of ions in a solution, the greater the conductivity
C6H12O6 (nonelectrolyte) < CH3COOH (weak electrolyte, existing mainly in the form of molecules with few ions) < NaCH3COO (strong electrolyte that provides two ions, Na+ and CH3COO-) < Ca(NO3)2 (strong electrolyte that provides three ions, Ca2+ and 2NO3-)
solution to stoichiometry and chemical analysis using mass relations in a neutralizing rxn, how many grams of Ca(OH)2 are needed to neutralize 25.0 mLof 0.100M HNO3?
Ca(OH)2(s) + 2HNO3(aq) -> Ca(NO3)2(aq) + 2H2O(l)
when a carbonate or hydrogen carbonate reacts with an acid, the products are a salt, carbon dioxide, and water:
CaCO3(s) + HCl(aq) -> CaCl2(aq) + CO2(g) + H2O(l) NaHCO3(aq) + HBr(aq) -> NaBr(aq) + CO2(g) + H2O(l)
The spectator ions in the reaction between aqueous chloric acid and aqueous barium hydroxide are __________.
ClO3- and Ba2+
A compound was found to be soluble in water. It was also found that addition of acid to an aqueous solution of this compound resulted in the formation of carbon dioxide. Which one of the following cations would form a precipitate when added to an aqueous solution of this compound?
Cr3+
to convert moles to grams, we need the molar mass, which we can calculate using the chemical formula and atomic weights. calculate the mass, in grams, of 0.433 mol of calcium nitrate, Ca(NO3)2
FW = 164.1 amu -> molar mass = 164.1 g/mol molar mass meaning 1 mol of calcium nitrate = 164.1 g/mol grams Ca(No3)2 = (0.433 mol Ca(NO3)2) (164.1 g Ca(NO3)2 / 1 mol Ca(NO3)2) = 71.1 g Ca(NO3)2
calculate the number of H atoms in 0.350 mol of C6H12O6 moles C6H12O6 -?molecules C6H12O6 -> atoms H
H atoms = (0.350 mol C6H12O6) (6.02 x 10^23 molecules C6H12O6 / 1 mol C6H12O6) x (12H atoms / 1 molecule C6H12O6) = 2.53 x 10^24 H atoms
CH3COOH(aq) -><- H+ (aq) + CH3COO-(aq) the half arrows pointing in opposite directions mean that the rxn is significant in both directions. at any given moment some CH3COOH molecules are ionizing to form
H+ and CH3COO- ions but H+ and CH3COO- ions are recombining to form CH3COOH this balance produces a state of chemical equilibrium. the relative numbers of each type of ion or molecule in the rxn are constant over time
protons in aqueous solution are solvated by water molecules, just as other cations are. in writing chemical equations involving protons in water, we write
H+(aq)
The net ionic equation for the reaction between aqueous nitric acid and aqueous sodium hydroxide is __________.
H+(aq) + OH-(aq) → H2O(l)
The balanced molecular equation for complete neutralization of H2SO4 by KOH in aqueous solution is __________.
H2SO4 (aq) + 2KOH (aq) → 2H2O (l) + K2SO4 (aq)
Which of the following are strong electrolytes? HCl HC2 H3O2 NH3 KCl
HCl, KCl
Which of the following are weak acids?
HF
Which of the following are strong acids? HI HNO3 HF HBr
HI, HNO3, HBr
bases are substances that do not react with H+ ions. compounds that do not contain
HO- ions can also be bases. NH3 is a common base. When added to water, it accepts an H+ ion from a water molecule and produces an HO- ion
What are the spectator ions in the reaction between KCl (aq) and AgNO3 (aq)?
K+ and NO3-
which ions remain in solution after Pbl2 precipitation is complete?
K+ and NO3-
what dissolved species are present in a solution of KCN
K+(aq) and CN-(aq)
the accompanying diagram represents an aqueous solution of either MgCl2, KCl, or K2SO4. which solution does the drawing best represent?
K2SO4 we examine each ionic substance given to determine the relative numbers and charges of its ions. we then correlate these ionic species with the ones shown i the diagram. the diagram shows twice as many cations as anions, consistent with the formulation K2SO4
to covert grams to moles, we need the molar mass, which we can calculate using the chemical formula and atomic weights. calculate the number of moles of glucose (c6H12O6) in 5.380g of C6H12O6.
MW = 180 amu Molar mass = 180 g/mol (meaning 1 mol of glucose is 180g) moles of C6H12O6 = (5.380g C6H12O6)(1 mol C6H12O6/180.0g C6H12O6) = 0.02989mol C6H12O6
Law of Conservation of Mass
Matter is not created nor destroyed in any chemical or physical change
the molarity of the new diluted solution can be determined from the equation Mc x Vc = Md x Vd where
Mc and Md are the molarity of the concentrated and dilute solutions Vc and Vd are the volumes of the two solutions
Which of the following reactions will not occur as written?
Mg(s) + Ca(OH)2(aq) → Ca(s) + Mg(OH)2(aq)
Which of the following is insoluble in water at 25 °C?
Mg3(PO4)2
Which one of the following compounds is insoluble in water?
MgC2O4
a nitrogen oxide is 63.65% by mass nitrogen. the molecular formula could be
N2O
Combining aqueous solutions of BaI2 and Na2SO4 affords a precipitate of BaSO4. Which ion(s) is/are spectator ions in the reaction?
Na+ and I-
because ionic substances exist as 3D arrays of ions, it is innapropriate to speak of molecules of these substances. instead we speak of the formula units. The formula unit for NaCl, for instance, consists of one
Na+ ion and one Cl- ion. the formula weight of NaCl is defined as the mass of one formula unit: FW of NaCl = 23.0 amu + 35.5 amu = 58.5 amu
what dissolved species are present in a solution of NaClO4?
Na+(aq) and ClO4- (aq)
which ions, if any, are spectator ions in the rxn AgNO3(aq) + NaCl(aq) -> AgCl(s) + NaNO3(aq)?
Na+(aq) and NO3-(aq)
when Na and S undergo a combination rxn, what is the chemical formula of the product?
Na2S
hydrogen sulfide (H2S) the substance that gives rotten eggs their soul odor, forms when acid such as HCl(aq) or H2SO4 reacts with a metal sulfide such as Na2S:
Na2S(aq) + 2HCl(aq) -> 2NaCl(aq) + H2S(g) Na2S(aq) + H2SO4(aq) -> Na2SO4(aq) +H2S(g)
In which species does nitrogen have the highest oxidation number?
NaNO3
which solute will cause the lightbulb to glow most brightly, Ch3OH, NaOH, or CH3COOH?
NaOH(aq)
Based on the equations below, which metal is the most active? Pb(NO3)2 (aq) + Ni (s) → Ni(NO3)2 (aq) + Pb (s) Pb(NO3)2 (aq) + Ag (s) → No reaction Cu(NO3)2 (aq) + Ni (s) → Ni(NO3)2 (aq) + Cu (s)
Ni
Zinc is more active than cobalt and iron but less active than aluminum. Cobalt is more active than nickel but less active than iron. Which of the following correctly lists the elements in order of increasing activity?
Ni < Co < Fe < Zn < Al
Which hydroxides are weak bases?
None of these is a weak base.
by analogy to examples given in the text, predict what gas forms when Na2SO3(s) reacts with HCl(aq)
SO2(g) Na2SO3(s) + 2HCl(aq) -> 2NaCl(aq) + SO2(g) + H2O(l)
what is the empiricial formula of a compound that contains 27.0% S, 13.4% O, and 59.6% Cl by mass?
SOCl2
Which one of the following is not true concerning 2.00 L of 0.100 M solution of Ca3(PO4)2?
This solution contains 0.800 mol of oxygen atoms.
The net ionic equation for the dissolution of zinc metal in aqueous hydrobromic acid is
Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g)
calculate the molarity of a solution made by dissolving 23.4g of sodium sulfate (Na2SO4) in enough water to form 125 mL of a solution depending on the chemical formula of the compound
a 1.0 M solution of NaCl is 1.0 M in Na+ ions and 1.0 M in Cl- ions. a 1.0 M solution of Na2SO4 is 2.0 M in Na+ ions and 1.0 M in SO4^2- ions the concentration of an electrolyte solution can be specified. in terms of the compound used to make the solution - 1.0 M Na2SO4, and in terms of the ions that the solution contains - 2.0 M Na+ and 1.0 M SO4^-2
arrhenius definition of a base
a base is a substance that, when dissolved in water, increases the concentration of hydroxide ions. bronsted-lowry definition of a base is: a base is a proton acceptor
H2SO4 is a strong electrolyte, only the first ionization is complete. aqueous solutions of sulfuric acid contain
a mixture of H+(aq), HSO4-(aq) and SO4^2-(aq)
does a rxn occur when an aqueous solution of NiCl2(aq) is added to a test tube containing strips of metallic zinc, and when NiCl2(aq) is added to a test tube containing Zn(NO3)2(aq)?
a rxn does occur when an aqueous solution is added to a test tube of metallic zinc a rxn does NOT occur when NiCl2(aq) is added to a tube containing Zn(NO3)2(aq)
chemists use half arrows pointing in opposite directions to represent the ionization of weak electrolytes. CH3COOH(aq) -><- H+(aq) + CH3COO-(aq) chemical equilibrium
a single arrow to represent the ionization of strong electrolytes. HCl(aq) -> H+(aq)+Cl-(aq) No left-point arrow, the H+ and Cl- ions have no tendency to recombine to form HCl molecules
different metals vary in the ease with which they are oxidized. Zn is oxidized by aqueous solutions of Cu2+. Ag is not oxidized by
acqueous solutions of Cu2+. Zn loses electrons more readily than Ag - Zn is easier to oxidize than Ag
we must be careful not to confuse the extent to which an electrolyte dissolves with whether it is strong or weak. CH3COOH is extremely soluble in water but is a weak electrolyte. Ba(OH)2 is not very soluble in water, but the amount of the substance that does dissolve dissociates
almost completely Ba(OH)2 is a strong electrolyte
Of the following elements, __________ is the most easily oxidized. oxygen fluorine nitrogen aluminum gold
aluminum
we begin to explore some important aspects of chemical change. the use of chemical formulas to represent rxns. the quantitative information we can obtain about the
amounts of substances involved in rxns.
because a hydrogen atom consists of a proton and an electron, H+ is simply a proton. acids are often called proton donors. the bronsted lowry definition of an acid is
an acid is a proton donor
acids are substances that ionize in aqueous solution to form hydrogen ions H+(aq). Arrhenius definition of an acid is
an acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions
titration is an analytical technique in which one can calculate the
concentration of a solute in a solution
precipitation rxns occur when pairs of oppositely charged ions attract each other so strongly that they form
an insoluble ionic solid. to predict whether certain combinations of ions from insoluble compounds, we must consider the guidelines of solubilities of common ionic compounds. Pb(NO3)2(aq) + 2Kl(aq) -? Pbl2(s) + 2KNO3(aq)
the activity series can be used to predict the outcome of rxns between metals and
and either metal salts or acids. any metal on the list can be oxidized by the ions of elements below it
water has an exceptional ability to dissolve a wide variety of substances. water on earth (drinkable or not) contains a variety of dissolved substances. a solution in which water is the dissolving medium is called an
aqueous solution. seawater is different from what we call freshwater because it has a much higher total concentration of dissolved ionic substances.
water is a very effective solvent for ionic compounds. positive ions (cations) are attracted by the negative end of H2O, and the negative ions (anions)
are attracted by the positive end
once we know the formulas of the reactants and products in a rxn, we can write an unbalanced equation. CH4(g) + O2(g) -> CO2(g) + H2O(g) because atoms are neither created nor destroyed in any rxn, a chemical rxn must first have an equal number of
atoms of each element on each side of the arrow. when the condition is met, the equation is said to be balanced.
one mole of atoms, ions or molecules contains avogadro's number of those particles. one mole of molecules or formula units contains
avogadros number times the number of atoms or ions of each element in the compound. we must always use the subscript!
coefficients are inserted to
balance the equation. they indicate the relative numbers of molecules of each kind involved in the rxn
how many H2) molecules are in a 9.00g sample of water? 1 molecule of H2O (18.0amu) -> (avogadros number) -> 1 mol of H2) (18.0g)
both masses have the same number but different units (atomic mass units and grams). expressing both masses in grams indicates their huge difference: 1 molecule of H2O has a mass of 2.99 x 10^-23g whereas 1 mol of H2O has a mass of 18.0g. 3.01 x 10^23
Of the choices below, which would be the best for the lining of a tank intended for use in storage of hydrochloric acid?
copper
to predict whether a precipitate forms when we mix aqueous solutions of two strong electrolytes, we must 1. note the ions present in the reactants 2. consider the possible cation-anion combinations 3. determine if any of these combinations is insoluble. will a precipitate form when solutions of Mg(NO3)2 and NaOH are mixed?
both substances are soluble ionic compounds and strong electrolytes. mixing the solutions first produces a solution containing Mg2+,Na+, HO- and NO3- ions our only possibilities are Mg2+ with HO- and Na+ with NO3-. hydroxides are generally insoluble. because is not an exception, Mg(OH)2 is insoluble - forms a precipitate. NaNO3 is soluble and remains in solution. Mg(NO3)2(aq) + 2NaOH(aq) -? Mg(OH)2(s) + 2NaNO3(aq)
a formula weight (fw) is the sum of the atomic weights (aw) for the atoms in a
chemical formula. i.e the formula weight of calcium chloride, CaCl2, would be Ca: 1 (40.1 amu) Cl: 2 (35.5 amu) ----------------- 111.1 amu formula weights are generally reported for ionic compounds
the properties of acidic solutions are quite different from those of basic ones. acids change the colors of certain dyes in a way that differs from the way bases affect the same dyes. acidic and basic solutions differ in
chemical properties. when a solution of an acid and a solution of a base are mixed, a neutralization rxn occurs. the products of the rxn have none of the characteristic properties of either the acidic solution or the basic solution. when hydrochloric acid is mixed with a solution of sodium hydroxide, the rxn is: HCl(aq) + NaOH(aq) -> NaCl(aq) + H2O(l)
chemical equations are concise representations of
chemical rxns i.e 2H2O + O2 -> 2H2O
the study of chemical changes is at the heart of
chemistry
balancing an equation = determine the coefficients that provide equal numbers of each type of atom on the two sides of the equation CH4(g) + 2O2(g) -> CO2(g) + 2H2O(g) the number o atoms obtained by multiplying each subscript in a chemical formula by the
coefficient for the formula. for most purposes, a balanced equation should contain the smallest possible whole-number coefficients.
titration is an analytical technique in which one can calculate the concentration of a solute in a solution. titration involves combining a solution where the solute concentration is not known with a reagent solution of known concentration - standard solution' just enough standard solution is added to
completely react with the solute in the solution of unknown concentration. the point at which stoichiometrically equivalent quantities are brought together is known as the equivalence point
what number would you use to convert moles of CH4 to grams of CH4?
molar mass of CH4, 16.0g CH4/1 mol CH4
molecules of different acids ionize to form different numbers of ions. both HCl and HNO3 are monoprotic acids, yielding one H+ per molecule of acid. HCl(aq) -> H+(aq) + Cl-(aq) HNO3(aq) -> H+(aq) + NO3-(aq) sulfuric acid, H2SO4, is a
diprotic acid, one that yields two H+ per molecule of acid. the ionization of H2SO4 and other diprotic acids occurs in two steps: H2SO4(aq) -> H+(aq) + HSO4-(aq) HSO4-(aq)-><- H+(aq) + SO4^2-(aq)
a nonelectrolyte may dissolve in water, but it does not
dissociate into ions when it does so.
an electrolyte is a substance that
dissociates into ions when dissolved into water
an acid is a substance (molecule or ion) that
donates a proton to another substance. a base is a substance that accepts a proton. HCl(g) + H2O(l) -> Cl-(aq) + H3O+(aq)
soluble ionic compounds tend to be
electrolytes
oxidation of calcium metal by molecular oxygen. the oxidation involves transfer of
electrons from the calcium metal to the O2 molecule - leading to formation of CaO
how do you explain the fact that the values in our calculated C:H:O ratio are 3.0:7.9:1.0 rather than exact integers 3:8:1?
experimental uncertainties in the experimental measurements
in what ways are the rxns depicted in the figures below alike? 1) fuel is a hydrocarbon 2) rxn is a decomposition type 3) oxygen is a reactant 4)products are water and carbon dioxide
fuel is a hydrocarbon (1) oxygen is a reactant (3) products are water and carbon dioxide (4)
the key to predicting the products formed by a given combination of reactants is recognizing
general patterns of chemical reactivity
the mole concept is a bridge that will allow us to use the atomic/formulas/ molecular weight and translate it into
grams. the same numbers will be valid, providing that we talk about 1 mole of those molecules. we must keep in mind that 18g of H2O do not contain 1 molecule, but contain avogadro's number, meaning 6.02 x 10^23. 1 molecule of H20 (18 amu) vs 1 mol of H2O (18.0g) the difference here is in units.
solutions are defined as homogeneous mixtures of two or more pure substances. the solvent is present in
greatest abundance. all other substances are solutes
the periodic table can be used to determine the molar mass of molecules and formula units as well. if the molecular mass is found i atomic mass units (amu), the molar mass of that molecule will
have the same value with the unit grams (g). i.e atomic nitrogen (N) formula weight = 14.0 molar mass (g/mol) = 14.0
solvation
helps stabilize the ions in a solution. prevents cations and anions from recombining. the ions and their shells of surrounding water molecules are free to move about. they become dispersed uniformly throughout the solution
combustion rxns are generally rapid rxns that produce a flame. combustion rxns most often involve
hydrocarbons reacting with oxygen in the air. if the starting compound has only carbon and hydrogen, the products will always be CO2 and H2O. every rxn is implying some kind of energy associated with it. there's always an energy matter associated with rxns. some rxns need energy to be preformed, some of them release energy into the environment
bases are substances that dissociate in aqueous solution to form hydroxyl ions HO-(aq) bases produce
hydroxide ions when they dissolve in water. ionic hydroxide compounds, such as NaOH, KOH, and Ca(OH)2 are among the most common bases NaOH(aq) -> Na+(aq) + HO-(aq) KOH(aq) -> K+(aq) + HO-(aq) Ca(OH)2(aq)-> Ca2+(aq) + 2HO-(aq)
weak electrolytes are those solutes that exist in solution mostly in the form of neutral molecules with only a small fraction in the form of ions.
i.e a solution of scetic acid HC2H3O2 (CH3COOH) most of the solute is prsent as CH3COOH(aq) molecules. Only a small fraction (about 1%) of the CH3COOH molecules has dissociated into anions. ionization rxn: CH3COOH(aq) -><- H+(aq) + CH3COO-(aq)
the empirical formula for a substance tells us the relative number of atoms of each element in the substance. the ratio of the numbers of moles of all elements in a compound gives the subscripts
in the compound's empirical formula. the mole concept provides a way of calculating empirical formulas.
how would the volume of standard solution added change if that solution were Ba(OH)2(aq) instead of NaOH(aq)?
increase by two the volume used for titration with NaOH
reactions that result in the formation of an insoluble product are called precipitation rxns. a precipitate is an
insoluble solid formed by a rxn in a solution. Pb(NO3)2(aq) + 2Kl(aq) -> Pbl2(s) + 2KNO3(aq)
adding just a few drops of hydrochloric acid would not be sufficient to dissolve all the Mg(OH)2(s). why not?
insufficient hydrogen ions are added to react with all of the solid magnesium hydroxide 2H3O+(aq) + Mg(OH)2(aq) -> Mg^2+(aq) + 4H2O(l)
when a molecular compound dissolves in water, the solution usually consists of
intact molecules dispersed throughout the solution. most molecular compounds are nonelectrolytes
what number would you use to convert number of molecules CH4 to moles of CH4?
inverse of avogadros number, 1 mol/6.02 x 10^23 molecules
what happens when an acid dissolves in water?
ionization reaction of HCl acid when dissolved in water: HCl(aq) -> H+(aq) + Cl-(aq) H+ ion interacts strongly with water molecules and forms the hydronium ion H3O+(aq) HCl(aq) -> H+(aq) + Cl-(aq) H+(aq) + H2O(aq) -> H3O+(aq)
the reactivity of an acid can depend on the anion as well as on the concentration Hydroflouric acid HF is a weak acid only partly
ionized in aqueous solution. it is very reactive and vigorously attacks many substances, including glass. this reactivity is due to the combined actions of H+ and F-
CH3COOH(aq) -><- H+(aq) + CH3COO-(aq) the molecule CH3COOH has 4 hydrogens. only one of them, the H in the COOH group, is
ionized in water. the three other hydrogen atoms are bound to carbon and do not break their bonds C-H in water
electrolytes differ in the extent to which they conduct electricity. strong electrolytes are those solutes that exist in solution completely or nearly completely as
ions. all water soluble ionic compounds (such as NaCl) Dissociation rxn: NaCl(s) -> Na+(aq) + Cl-(aq) a few molecular compounds (such as HCl) are strong electrolytes. Ionization rxn: HCl(aq) -> H+(aq) + Cl-(aq)
can we predict whether a certain metal will be oxidized either by an acid or by a particular salt?
it would be uniwse to store a solution of nickel nitrate in an iron container because the solution would dissolve the container. Fe(s) + Ni(NO3)2(aq) -> Fe(NO3)2(aq) + Ni(s) Fe(s) + Ni^2+(aq) ->Fe2+(aq) + Ni(s)
it is helpful to pay attention to exactly what species are present in a reaction mixture (i.e solid, liquid, gas, aqueous solution). if we are to understand reactivity, we must be aware of
just what is changing during the course of a reaction
reactants appear on the
left side of the equation
to form the net ionic equation, cross out anything that does not change from the
left side of the equation to the right. the only species left in the equation are those that change (i.e react) during the course of the rxn. Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) -> AgCl(s) + K+(aq) + NO3-(aq) becomes: Ag+(aq) + Cl-(aq) -> AgCl(s) those species that did not change (and were deleted from the net ionic equation) are called spectator ions
an oxidation occurs when an atom or ion
loses electrons a reduction occurs when an atom or ion gains electrons one cannot occur without the other
avogadros number represents the number of atoms or molecules in 1 mole, it is a bridge. you take this bridge from the microscopic realm into the
macroscopic realm. you dont see it as a single molecule but you see it as a laboratory sized sample.
Which of these metals will be oxidized by the ions of aluminum?
magnesium
the real reason for packing 6.02 x 10^23 items into a mole is because there are 6.02 x 10^23 amu (atomic mass units) in one gram. this allows us to use the mass numbers on the periodic table for both the
mass of an atom (atomic mass) and the mass of a mole of atoms (molar mass, we only needed to change the units. 1 amu = 1.66054 x 10^-24g 1g = 6.0221 x 10^23 amu
we are going to have a lot of atoms in a mole because of their very low
mass. the atomic weight is in amu. we can convert amu to grams using the concept of moles
the reason we need so many items in a mole. we need to group molecules in very large groups in order to be able to get a
measurable reading on our balances. we cannot find the mass of one atom, or even one gross of atoms, on our laboratory balances, the instruments are not sensitive enough. we can find the mass one one mole of atoms on our balance.
the mass in grams of one mol of any element - 6.02 x 10^23 atoms - is the
molar mass of that element. molar mass (M) g/mol (grams per mole) an element's molar mass is the quantity in grams numerically equal to it's atomic weight
the definition of molarity contains 3 quantities - molarity, moles solute and liters of solution. if we know any two of these, we can calculate the third
molarity (M) = moles of solute/ volume of solution in liters
which has more mass, a mole of water or a mole of glucose?
mole of glucose
a molecular weight (mw) is the sum of the atomic weights of the atoms in a
molecule. i.e for the molecule ethane, C2H6, the molecular weight would be C: 2(12.0 amu) H: 6(1.0 amu) --------------- 30.0 amu molecular weights are generally reported for molecular compounds.
A weak electrolyte exists predominantly as __________ in solution
molecules
subscripts tell the number of atoms of each element in a molecule. coefficients tell the number of
molecules
How many millimeters of 3.0 M H2SO4 are needed to make 450 mL of 0.10 M H2SO4?
moles H2SO4 in dilute solution = (0.450 soln)(0.10 mol H2SO4/1 L soln) = 0.045 mol H2SO4 L conc soln = (0.045 mol H2So4)(1L soln/3.0 mol H2SO4) = 0.015 L soln or using Mc x Vc = Md x Vd (3.0 M)(V conc) = (0.10 M)(450 mL) (V conc) = (0.10 M)(450 mL)/3.0 M = 15mL
grams <- use molar mass -> moles <- use NA -> formula units-> atoms
moles is central. we can go both ways.from moles to formula units and from formula units to atoms. we can also go from moles to grams
molarity (symbol M) expresses the concentration of a solution as the number of
moles of solute in a liter of solution. molarity is one way to measure the concentration of a solution. molarity (M) = moles of solute/ volume of solution in liters
avogadro's number is a connection between the weight that we measure and the number of atoms and molecules. avogadros number is connected to the concept of
moles. the mole is a unit of grouping - what the items are does not matter. you can have a mole of molecules, a mole of ions, or a mole of stars. the number of items in a mole will always be: 6.02 x 10^23 - Avogadro's number
scientists use the term concentration to designate the amount of solute dissolved in a given quantity of solvent or a quantity of solution. the concept of concentration is intuitive. the greater the amount of solute dissolved in a certain amount of solvent, the
more concentrated the resting solution. in chemistry we often need to express the concentrations of solutions quantitatively
to determine if an oxidation reduction reaction has occurred, we assign an oxidation number to each element in a
neutral compound or charged entity
what is the oxydation number of nitrogen in aluminum nitride, AIN and in nitric acid, HNO3?
nitrogen - -3 AIN - +5
molecular compounds tend to be
nonelectrolytes (except for acids and bases)
in combination rxns, two or more substances react to form
one product. many elements react with one another in this way to form compounds. i.e 2Mg(s) + O2(g) -> 2MgO(s) N2(g) + 3H2(g) -> 2NH3(g) 2Na(s)+ Cl2(g) -> 2NaCl(s)
which is the more easily reduced, Mg2+(aq) or Ni2+(aq)?
only those metals above hydrogen in the activity series are able to react with halo-acids to form H2. Ni reacts with Hcl(aq) to form H2 Ni(s) + Hcl (aq) -> NiCl2(aq) + H2(g) Cu does not react with HCl, but reacts with HNO3 Cu(s) + 4HNO3(aq) -> Cu(No3)2(aq) + 2No2(g) + 2H2O(l)
the states of the reactants and products are written in
parentheses to the right of each compound i.e CH4(g) + 2O2(g) -> CO2(g) + 2H2O(g)
not all substances that dissolve in water make the resulting solution conducting. there must be a current - a flow of electrically charged
particles between the two electrodes immersed in the solution the conductivity of pure water is not sufficient to complete the electrical circuit and light the bulb
one can calculate the empirical formula from the
percent composition
we learn not to bring electrical devices into the bathtub so as not to electrocute ourselves. most of the water you encounter on a daily life is electrically conducting. pure water is a very
poor conductor of electricity. the conductivity of bathwater originates from the substances dissolved in the water, not from the water itself.
nonmetals tend to have negative oxidation numbers, although some are
positive in certain compounds or ions. oxygen has an oxidation number of -2 except in the peroxide ion in which it has an oxidation number of -1. hydrogen is -1 when bonded to a metal, +1 when bonded to a nonmetal
one finds the percent yield by comparing the amount actually obtained (actual yield) to the amount it was
possible to make (theoretical yield) percent yield = actual yield/theoretical yield x 100
the solubility of a substance at a given temperature is the amount of a substance that can be dissolved in a given quantity of solvent at the given
temperature. any substance with a solubility less than 0.01 mol/L will be referred to as insoluble the attraction between the oppositely charged ions in the solid is too great for the water molecules to separate the ions to any significant extent. the substance remains largely undissolved.
net ionic equations are widely used to illustrate the similarities between large numbers of rxns involving electrolytes. for example, Ag+(aq) + Cl-(aq) -> AgCl(s) expresses the essential feature of the precipitation rxn between any strong electrolyte containing Ag+ and any strong electrolyte containing Cl-. The Ag+ and Cl- ions combine to form a
precipitate of AgCl. a net ionic equation demonstrates that more than one set of reactants can lead to the same net rxn. for example, aqueous solutions of NaCl and KCl share many chemical similarities - both contain ions. AgNO3(aq) + KCl(aq) -> AgCl(s) + KNO3(aq) AgNO3(aq) + NaCl(aq) -> AgCl(s) + NaNO3(aq) the complete equation identifies the actual reactants that participate in a rxn - NaCl and AgNO3 or KCl and AgNO3. becomes: Ag+(aq) + Cl-(aq) -> AgCl(s)
chemical formulas and chemical equations both have a quantitative significance. the subscripts in formulas and the coefficients in equations represent
precise quantities. the formula H2O indicates that a molecule of water contains exactly 2 atoms of hydrogen and 1 atom of oxygen. similarly, the coefficients in a balanced chemical equation indicate the relative quantities of reactants and products.
combustion analysis deals with
preforming a combustion rxn for a substance compounds containing C, H, and O are routinley analyzed through combustion in a chamber: - C is determined from the mass of CO2 produced - H is determined from the mass of H2O produced - O is determined by difference after the C and H have been determined
the mole will always allow us to do many of the important calculations that are required for
quantitative analysis of samples in the lab. when we use molecules in calculations we will abbreviate the units to mol. when we show the molar mass of a substance we will show the units in g/mol
if we have a rxn and there are coefficients, you can evaluate it at a molecular level or at a mole level. the only difference is the units. the coefficients in the balanced equation give the
ratio of moles of reactants and products
in displacement reactions, ions oxidize an element. the ions are then
reduced
Oxidation cannot occur without __________.
reduction
products appear on the
right side of the equation
elements in their elemental forms have an oxidation number of 0. the oxidation number of a monoatomic ion is the
same as its charge
the limiting reactant is the reactant present in the
smallest stoichiometric amount. in other words, its the reactant you'' run out of first i.e 10H2 and 7O2 -> 10H2O and 2O2 (no H2 molecules) the limiting reactant is H2 and O2 is the excess reagent
water and table salt, NaCl, are the products of the rxn. the term dalt has come to mean any ionic compound whose cation comes from a base (i.e from NaOH) and whose anion comes from an acid (i.e HCl). a neutralization rxn between an acid and a metal hydroxide produces water and a salt. when hydrochloric acid (strong acid) is mixed with a solution of
sodium hydroxide (strong bases), the rxn is HCl(aq) + NaOH(aq) -> NaCl(aq) + H2O(l) H+(aq) + Cl-(aq)+ Na+(aq) + OH-(aq) -> Na+(aq) + Cl-(aq) + H2O(l) becomes: H+(aq) + OH-(aq) -> H2O(l) becomes: H3O=(aq) + OH-(aq) ->2H2O(l)
there are no rules based on simple physical properties such as ionic charge to guide us in predicting whether a particular ionic compound will be soluble. experimental observations have lead to guidelines for predicting
solubility for ionic compounds. all common ionic compounds that contain the nitrate anion, NO3- are soluble in water. all common ionic compounds of the alkali metal ions (group 1A of the periodic table) and of the ammonium ion NH4+ are soluble in water.
when an ionic substance dissolves in water, the solvent pulls the individual ions from the crystal and
solvates them. this process is called dissociation dissociation: NaCl(s) -> Na+(aq) + Cl-(aq)
acids and bases that are strong electrolytes - completley ionized in solution - are
strong acids and strong bases. those that are weak electrolytes (partly ionized) are weak acids and weak bases. when reactivity depends only on concentration, strong acids are more reactive than weak acids
Strong electrolytes are
strong acids, strong bases, soluble ionic salts
stoichiometry is the area of study that examines the quantities of
substances consumed and produced in chemical rxns. the name is derived from the greek stoicheion (element) and metron (measure)
many bases besides those that contain HO- react with H+ to form molecular compounds. two of these that you might encounter in the laboratory are (theres 3):
sulfide ion carbonate ion sulfite ion all of these anions will react with acids to form gases that have low solubilities in water
Which one of the following is a diprotic acid?
sulfuric acid
what is the difference in atom count between the notation CO2 and the notation 2CO?
the first notation shows one carbon atom and two oxygen atoms whereas the second one shows two carbon atoms and two oxygen atoms.
how is the molarity of a 0.50 M KBr solution changed when water is added to double its volume?
the new concentration is 0.25 M
the metal is oxidized by HCl, producing H2 and MgCl2(aq) Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g) 0 +1 -1 +2 -1 0
the oxidation number of Mg changes from 0 to +2 the increase in the oxidation number indicates that the atom has lost electrons - has therefore been oxidized the H+ ion of the acid decreases in oxidation number from +1 to 0. this ion has gained electrons and has therefore been reduced the oxidation number of the Cl- ion remains -1 it is a spectator ion in the rxn
chemists must sometimes calculate the percentage composition of a compound. the percentage by mass contributed by each element in a substance. forensic chemists will measure the percentage composition of an unknown powder and compare it with
the percentage compositions for sugar, salt, or unknown substance to identify it
grams of substance a -> use molar mass of a -> moles of substance a -> use coefficients of a and b from balanced equation -> moles of substance b -> use molar mass of b -> grams of substance b starting with the mass of substance a, you can use
the ratio of the coefficients of a and b to calculate the mass of a substance B formed (if its a product) or used (if its a reactant)
CH4(g) + O2(g) -> CO2(g) + H2O(g) it is usually best to balance those elements that occur in the fewest chemical formulas in the equation. C and H appear each in only one reactant and product. we start with balancing C. One molecule of CH4 contains
the same number of C atoms as one molecule of CO2. the coefficients for CH4 and CO2 must be the same in the balanced equation - 1 - unwritten. next we focus on H. CH4 contains 4 H atoms and H2O contains 2 H atoms. We balance the H atoms by placing the coefficient 2 in front of H2O. There are 4 H atoms on each side of the equation Next we balance O. A coefficient 2 in front of O2 balnaces the equation by giving 4 O atoms on each side (2x2 on the left, 2+2x1 on the right)
in the ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into
their ions. this more accurately reflects the species that are found in the rxn mixture. Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) -> AgCl(s) + K+(aq) + NO3-(aq)
which contains more molecules, a mole of water or a mole of glucose?
they both contain the same number of molecules
Of the metals below, only __________ will not dissolve in an aqueous solution containing nickel ions. aluminum chromium barium tin potassium
tin
a few molecular substances have aqueous solutions that contain ions. acids are the most important of these solutions. when HCl(g) dissolves in water
to form hydrochloric acid, Hcl(aq), it ionizes in H+(aq) and Cl-(sq) ions ionization: HCl(aq) -> H+(aq) + Cl-(aq)
in a decomposition rxn, one substance breaks down into
two or more substances. many compounds react this way when heated. note: not every combination rxn has a decomposition rxn. i.e CaCO3(s) -> CaO(s) + CO2(g)
Mixing 10.00 mL of an aqueous solution with 10.00 mL of water represents a __________.
twofold dilution
when NaCl dissolves in water, the solution contains Na+ and Cl_ ions, each surrounded by
water molecules. ions carry electrical charge from one electrode to the other, completing the circuit
solutes are said to be dissolved in the solvent. when a small amount of sodium chloride (NaCl) is dissolved in a large quantity of
water, water is the solvent and NaCl is the solute
isopropyl alcohol, sold as rubbing alcohol, is composed of C, H, and O. Combustion of 0.255g of isopropyl alcohol produces 0.561g of CO2 and 0.306g of H2O. Determine the empirical formula of isopropyl alcohol.
we can use the mole concept to calculate - grams of C in the CO2 - grams of H in the H2O these masses are the masses of C and H in the alcohol before combustion. the mass of O in the compound equals the mass of the origional sample minus the sum of the C and H masses.
how do we relate the numbers of atoms or molecules to the numbers we measure in the laboratory?
we cannot directly count the atoms or molecules we can indirectly determine their numbers if we know their masses
it is the number of items that is always the same, not the mass or
weight or size of those items
the theoretical yield is the quantity of product calculated to form
when all of a limiting reactant is consumed. this is different from the actual yield, which is the amount one actually produces and measures. actual yield can never be greater than the theoretical yield.
dilution
when solvent is added to a solution, the number of moles of solute remains unchanged. moles solute before dilution = moles solute after dilution
this multiple can be found bu dividing the molecular weight by the empirical formula weight: whole # multiple = molecular weight/ empirical formula weight the empirical formula weight for ascorbic acid is C3H4O3. MW = 3(12 amu) + 4(1.0 amu) + 3(16 amu) = 88 amu the experimentally determined molecular weight is 176 amu
whole # multiple = molecular weight/empirical formula weight = 176 amu/88.0 amu we multiply the subscripts in the empirical formula by this multiple the molecular formula is C6H8O6
we can obtain a molecular formula for any compound from its empirical formula if we know either the molecular weight or the molar mass of the compound. the subscripts in the molecular formula of a substance are always
whole number multiples of the subscripts in its empirical formula