Chemistry Chapter 3 and 4 EXAM STUDY GUIDE

stoichiometric amounts

in the proportions indicated by the balanced equation

Francis William Aston

invented mass spectrometer; awarded Nobel Peace Prize in Chemistry 1922

double replacement reactions (metathesis)

involves the exchanging of parts between 2 compounds

spectators ions

ions that appear on reactant and product side

spectator ions

ions that do not participate in a reaction

how do you determine the molecular weight of a compound

looking at the average mass of a substance molecules ex. C2H4= 28.05 amu

What is the molarity of a solution made by dissolving 2.355g of sulfuric acid (H2SO4) in water and diluting to a final volume of 50.0 mL?

m=0.480 mol/L

percent composition by mass

mass of solute/mass of solution x 100%

M=

mol/L

molarity (M)

moles of solute/liters of solution

percent composition of an element in a compound equation

(n x molar mass of element/ molar mass of compound) x 100%

A 20.0 mL sample of hydrochloric acid (HCl) is titrated and found to react with 42.6 mL of 0.100 M NaOH. What is the molarity of the hydrochloric acid solution?

0.213 M HCl

How many moles of glucose, which is used to treat low blood sugar, are in a tablet containing 2.00g?

0.0111 mol

How many moles are in 5.26 g of NaHCO3, the main ingredient in Alka- Seltzer tablets?

0.0626 mol

What volume of 1.000 M NaOH solution is required to prepare to 500.0 mL of 0.2500 M NaOH?

0.125 L NaOH

What is the total molar concentration of ions in a 0.350 M solution of the strong electrolyte Na2SO4, assuming complete dissociation?

1.05 M

Diluted Solution

preparation of a less concentrated solution from a more concentrated solution

Stomach acid, a dilute solution of HCl in water, can be neutralized by reaction with sodium hydrogen carbonate, NaHCO3... How many milliliters of 0.125 M NaHCO3 solution are needed to neutralize 18.0mL of 0.100 M HCl?

14.4 mL NaHCO3

solvent

present in large amounts

Aqueous solutions of sodium hypochlorite (NaOCl), best known as household bleach, are prepared by reaction of sodium hydroxide with chlorine. How many grams of NaOH are needed to react with 25.0 g of Cl2?

28.2 g NaOH

Aqueous hydrochloric acid reacts with zinc metal to yield hydrogen gas and aqueous zinc chloride. Write a net ionic equation for the process and identify the spectator ions.

2H+ (aq) + Zn (s) --> H2 (g) + Zn2+ (aq)

Hydrochloric acid (HCl) is sold commercially as a 12.0 M aqueous solution. How many moles of HCl are in 300.0 mL of 12.0 M solution?

3.6 mol HCl

solute

present in small amounts and substance that is being dissolved

Avogadro's number ( in honor of the Italian scientist Amedeo Avogadro)

6.022 x 10^23 (The number of particles in exactly one mole of a pure substance)

Cisplatin, an anticancer agent used for the treatment of solid tumors, is prepared by the reaction of ammonia with potassium tetrachloroplatinate. Assume that 10.0 g of K2PtCl4 and 10.0g of NH3 are allowed to react. a. Which reactant is limiting, and which is in excess? How many grams of cisplatin are formed?

7.23 g; K2PtCl4 = limiting reactant

precipitate

A solid that forms from a solution during a chemical reaction.

Reactants

A starting material in a chemical reaction

Methyl term-butyl ether (MTBE, C5H12O), a gasoline addictive now being phased out in many places because of health concerns, can be made by reaction of isobutylene (C4H8) with methanol (CH4O). What is the percent yield of the reaction if 32.8 g of MTBE is obtained from reaction of 26.3 g of isobutylene with sufficient methanol?

79.4%

electrolyte

A substance that dissolves in water to give a solution that conducts electric current

solute

A substance that is dissolved in a solution.

Solvent

A liquid substance capable of dissolving other substances

solubility

A measure of how much solute can dissolve in a given solvent at a given temperature.

limiting reactant

A reactant that is totally consumed during a chemical reaction, limits the extent of the reaction, and determines the amount of product.

chemical equation

A representation of a chemical reaction that uses symbols to show the relationship between the reactants and the products

dilution

Adding water to a solution in order to decrease the concentration

The C60 molecule is called buckminsterfullerene because its shape resembles the geodesic domes designed by the visionary architect R. Buckminister Fuller. What is the mass (in grams) of one C60 molecule?

Because one C60 molecule contains 60 C atoms, and 1 mole of C contains 6.022 x 10^23 C atoms and has a mass of 12.01 g, we can calculate the mass of one C60 molecule as follows... 1 C60 molecule x (60 C atoms/1 C60 molecule) x (1 mol C/6.022 x 10^23 C atoms) x (12.01 g/1 mol C) = 1.197 x 10^-21 g

Propane, C3H8, is a colorless, odorless gas often used as a heating and cooking fuel in campers and rural homes. Write a balanced equation for the combustion reaction of propane with oxygen to yield carbon dioxide and water.

C3H8 + 5O2 --> 3CO2 + H2O

weak electrolytes

DO NOT completely dissociate/ionize in H2O (conduct very little electricity)

Hydrogen Replacement

Examples: 2Na (s) + 2H2O (l)-> 2NaOH (aq) + H2 (g) Ca (s) + 2 H2O (l) -> Ca(OH)2 (s) + H2 (g)

Halogen Displacement

F2, Cl2, Br2, I2

Boron is used in the manufacture of ceramics and polymers such as fiberglass. The atomic masses of its two isotopes. B(19.80 percent) and B (80.20 percent), are 10.0129 amu and 11.0093 amu respectively. The boron-10 isotope is also important as a neutron- capturing agent in nuclear reactors. Calculate the average atomic mass of boron. (PAGE 80)

Find the percent abundances are converted to fractions: 19.80 percent to 19.80/100 or 0.1980 and 80.20 percent to 80.20/100 or .8020. We find the contribution to the average atomic mass for each isotope, and then add the contributions together to obtain the average atomic mass. (0.1980)(10.0129amu) + (0.8020)(11.0093amu) = 10.8129

Name the following acid H2S (aq)

Hydrogen sulfide

Name the following acid HBrO (aq)

Hypobromous acid

Ascorbic acid (vitamin C) cures scurvy. It is composed of 40.92 percent carbon (C) 4.58 percent hydrogen (H), and 54.50 percent oxygen (O) by mass. Determine its empirical formula

If we have 100 g of ascorbic acid, then each percentage can be converted directly to grams. In this sample, there will be 40.92 g of C, 4.58 of H, and 54.50 g of O. Because the subscripts in the formula represent a mole ratio, we need to convert the grams of each element to moles. The conversion factor needed is the molar mass of each element. let n represent the number of moles each element has... NC- 40.92 g C x (1 mol C/12.01 g C) =3.407 mol C NH= 4.58 g H x (1 mol H/ 1.008 g H) = 4.54 mol H NO=54.50 g O x (1 mol O/ 16.00 g O) =3.406 mol O Thus, we arrive at the formula C3.407H4.54O3.406, which gives the identity and the mole ratios of atoms present. However, chemical formulas are written with whole numbers. Try to convert to whole numbers by dividing all the subscripts ny the smallest subscript (3.406): C: (3.407/3.406)= 1 H: (4.54/3.406)= 1.33 O: (3.406/3.406)=1 Where the = sign means "approximately equal to". This gives CH1.33O as the formula for ascorbic acid. Next, we need to convert 1.33, the subscript for H, into an integer. This can be done by a trial-and-error procedure: 1.33 x 1 = 1.33 1.33 x 2 = 2.66 1.33 x 3 = 3.99 Because 1.33 x 3 gives us an integer (4), we multiply all the subscripts by 3 and obtain C3H4O3, as the empirical formula for ascorbic acid.

Write both an ionic equation and a net ionic equation for the neutralization reaction of aqueous Her and aqueous Ba(OH)2

Ionic: 2H+(aq) + 2Br-(aq) + Ba2+(aq) +2OH-(aq) ->2H2O(l) + Ba2+ (aq) +2Br- (aq) Net Ionic: 2H+ (aq) + 2OH-(aq) -> 2H2O (l)

IMPORTANT INFO

It is possible to determine the molar mass of a compound without knowing its chemical formula

Molarity abbreviation

M

procedure for calculating empirical formula of a compound from its percent compositions

Mass percent--(convert to grams and divide by the molar mass)--> Moles of each element--(divide by the smallest number of moles)---> Mole ratios of elements---( change to integer subscripts)---> Empirical formula

What is the molecular weight of glucose (C6H12O6), and what is its molar mass in grams per mole?

Molar mass--> 180.18 g/mol

oxidation number

Positive or negative number that indicates how many electrons an atom has gained, lost, or shared to become stable

Methane (CH4) is the principal component of natural gas. How many moles of CH4 are present in 6.07 g of CH4?

The conversion factor needed to convert between grams and moles is the molar mass. First we need to calculate the molar mass of CH4, following the procedure in 3.5... molar mass of CH4= 12.01 g + 4(1.008 g) =16.04 g Because... 1 mol CH4 = 16.04 g CH4 the conversion factor we need should have been grams in the denominator so that the unit g will cancel, leaving the unit mol in the numerator 1 mol CH4/16.04 g CH4 We now write... 6.07 g CH4 x (1 mol CH4/16.04 g CH4) = 0.378 mol CH4

Helium (He) is a valuable gas used in industry, low-temperature research, deep sea diving tanks, and balloons. How many moles of He atoms are in 6.46g of He?

The conversion factor needed to convert between grams and moles is the molar mass. In the periodic table, we see that the molar mass of He is 4.003 g. This can be expressed as... 1 mol He= 4.003 g He From this equality, we can write two conversion factors, 1 mole He/4.003 g He and 4.003 g He/1 mole He The conversion factor on the left is the correct one. Grams will cancel, leaving the unit mol for the answer- that is... 6.46 g He x (1 mol He/4.003 g He)= 1.61 mol He

Zinc (Zn) is a silvery metal that is used in making brass (with copper) and in plating iron to prevent corrosion. How many grams of Zn are in 0.356 mole of Zn?

The conversion factor needed to convert between moles and grams is the molar mass. In the periodic table, we see the molar mass of Zn is 65.39 g. This can be expressed as 1 mol Zn= 65.39 g Zn From this equality we can write two conversion factors 1 mol Zn/ 65.39 g Zn AND 65.39 g Zn/1 mol Zn The conversion factor on the right is the correct one. Moles will cancel, leaving the unit of grams for the answer- that is... 0.356 mol Zn x (65.39 g Zn/1 mol Zn) = 23.3 g Zn

oxidizing agent

The electron acceptor in a redox reaction

Phosphoric Acid (H3PO4) is a colorless, syrupy liquid used in detergents, fertilizers, toothpastes, and in carbonated beverages for a "tangy" flavor. Calculate the percent composition by mass of H, P, and O in this compound

The molar mass of H3PO4 is 97.99 g. The percent by mass of each of the elements in H3PO4 is calculated... %H= ((3(1.008g)H)/97.99 g H3PO4) x 100%=3.086% %P=(30.97 g P/97.99 g H3PO4) x100% = 31.61 % %O= ((4(16.00g) O/97.99 g H3PO4) x 100% =65.31%

Chalcopyrite (CuFeS2) is a principal mineral of copper. Calculate the number of kilograms of Cu in 3.71 x 10^3 kg of chalcopyrite.

The molar masses of Cu and CuFeS2 are 63.55 g and 183.5 g, respectively. The mass percent of Cu is therefore... %Cu= molar mass of Cu/ molar mass of CuFeS2 x 100% = (63.55g/183.5g) x 100%= 34.63% To calculate the mass of Cu in a 3.71 x 10^3 kg sample of CuFeS2, we need to convert the percentage to a fraction (that is, convert 34.63 percent to 34.63/100 or 0.3463) and write mass of Cu in CuFeS2=0.3463 x (3.71 x 10^3 kg) = 1.28 x 10^3 kg

molecular mass

The sum of the masses of all the atoms in a molecule; sometimes called molecular weight. Example: 2 (atomic mass of H) + atomic mass of O 2 (1.008 amu) +16.00 amu = 18.02 amu

Calculate the molecular masses (in amu) of the following compounds (a) sulfur dioxide (SO2), a gas that is responsible for acid rain (b) caffeine (C8H10N4O2), a stimulant present in tea, coffee, and cola beverages

To calculate molecular mass, we need to sum all the atomic masses in the molecule. For each element, we multiply the atomic mass of the element by the number of atoms of that element in the molecule. We find atomic masses in the periodic table (a) There are two O atoms and one S atom in SO2, so that... molecular mass of SO2=32.07 amu + 2(16.00 amu) = 64.07 (b) There are eight C atoms, ten H atoms, four N atoms, and two O atoms in caffeine, so the molecular mass of C4H10N4O2 is given by... 8(12.01 amu) + 10(1.008 amu) + 4(14.01 amu) + 2(16.00 amu) = 194.20 amu

decomposition reaction

a reaction in which a single compound breaks down to form two or more simpler substances Ex: 2HgO (s) --> 2 Hg (l) + O2 (g) 2KClO3 (s) --> 2KCl (s) + 3O2 (g)

precipitation reaction

a reaction in which an insoluble substance forms and separates from the solution

reversible reaction

a reaction in which the conversion of reactants into products and the conversion of products into reactants occur simultaneously

How many hydrogen atoms are present in 25.6 g of urea [(NH2)2CO], which is used as a fertilizer, in animal feed, and in the manufacture of polymers? The molar mass of urea is 60.06 g.

To calculate the number of H atoms, we first must convert grams of urea to moles of urea using the molar mass of urea. This part is similar to 3.2. The molecular formula of urea shows there are four moles of H atoms in one mole of urea molecule, so the mole ratio is 4:1. Finally, knowing the number of moles of H atoms, we can calculate the number of H atoms using Avogadro's number. We need two conversion factors: molar mass and Avogadro's number. We can combine these conversions grams of urea-> moles of urea-> moles of H-> atoms of H into one step: 25.6 g (NH2)2CO x (1 mol (NH2)2CO/60.06 g (NH2)2CO) x (4 mol H/1 mol (NH2)2CO) x (6.022 x 10^23 H atoms/ 1 mol H) = 1.03 x 10^24 H atoms

metathesis reaction

a reaction that involves the exchange of parts between two compounds

Will a precipitation reaction occur when aqueous solutions of CdCl2 and (NH4)2S are mixed?

YES

reduction reaction

a chemical change in which electrons are gained, either by the removal of oxygen, the addition of hydrogen, or the addition of electrons

combination reaction

a chemical change in which two or more substances react to form a single new substance Ex: S (s) + O2 (g) --> SO2 (g) 2 Al (s) + 3 Br2 (l) --> 2AlBr3 (s)

combustion reaction

a chemical reaction that occurs when a substance reacts with oxygen, releasing energy in the form of heat and light Ex : C3H8 (g) + 5O2 (g) --> 3 CO2 (g) + 4H2O (l)

atomic mass unit

a mass exactly equal to one-twelfth the mass of one carbon-12 atom

titration

a measured amount of a solution of unknown concentration is added to a known volume of a second solution until the reaction between them is just complete

metal displacement

a metal in a compound can be displaced by another metal in the elemental state

Conversion Factors

a ratio of equivalent measurements

product

a substance that forms in a chemical reaction

Assign the Oxidation numbers to each atom in the following substances: a. CdS b. AlH3 c. S2O3(2-) d. Na2Cr2O7

a. Cd-> +2 S->-2 b. Al-> +3. H-> -1 c. S-> +2. O-> -2 d.Na-> +1. Cr-> +6. O-> -2

Predict whether the following redox reactions will occur (activity serie: a. Hg2+(aq) +Zn (s)-> Hg(l) +Zn2+ (aq) B. 2H+ (aq) +Cu(s) -> H2(g) + Cu2+(aq)

a. YES b. no

Assign oxidation numbers to all atoms, tell in each case which substance is undergoing oxidation and which reduction, and identify the oxidizing and reducing agents. a. Ca(s) +2H+ (aq) -> Ca2+ (aq) + H2(g) b. 2Fe2+ (aq) + Cl2 (aq) -> 2Fe3+ (aq) + 2Cl- (aq)

a. reducing agent- calcium oxidizing agent- hydrogen b. reducing agent- iron oxidizing agent- chlorine

Bronsted-Lowry base

accepts H+

acid-base neutralization

acid +base -> salt + H2O

percent yield equation

actual yield/theoretical yield x 100

standard solution

added gradually to another solution of unknown concentration, until the chemical reaction between the two solutions is complete

atomic mass units

amu

monoprotic acid

an acid that can donate only one proton (hydrogen ion) per molecule

triprotic acid

an acid that has three ionizable protons per molecule, such as phosphoric acid

diprotic acid

an acid that has two ionizable hydrogen atoms in each molecule, such as sulfuric acid

gravimetric analysis

an analytical technique based on the measurement of mass

disproportionation reaction

an element in one oxidation state is simultaneously oxidized and reduced

net ionic equation

an equation for a reaction in solution showing only those particles that are directly involved in the chemical change

oxidation-reduction reaction

any chemical change in which one species is oxidized (loses electrons) and another species is reduced (gains electrons); also called redox reaction

atomic mass=

atomic weight

Solubility rules

can predict if a precipitation reaction will occur

Carbon-12

carbon isotope that has six protons and six neutrons

strong electrolytes

completely dissociate/ionize in H2O (conduct electricity)

Molarity

concentration of a solution-> amount of solute in a given amount of a solvent

electrolytes

conduct electricity when dissolved in H2O

hydronium ion

hydrogen ion combines with a water molecule to form a hydronium ion, H3O(+)

Arrhenius base

dissociates in water to produce OH- ions

nonelectrolytes

don't conduct electricity when dissolved in H2O

arrlenius acid

donate H+ (hydrogen ion) (aq) solution

bronsted-lowry acids

donate H+ in solution

reducing agent

electron donor

lewis acids

electron pair acceptors

Lewis base

electron pair donor

Balancing chemical equartions

find out how many formula units of each substance take part in the chemical reaction

solution

homogenous mixture of 2 or more substances

oxidation-reduction reactions

one or more e- are transferred between atoms, molecules, or ions

excess reactants

reactants leftover when a reaction stops

ionic equations

removes spectator ions

HA

represents the acid

MOH

represents the base

ionic equation

shows dissolved species as free ions

precipitation reaction

strong electrolytes yield on insoluble solid product called the precipitate-> falls out of solution

indicators

substances that have distinctly different colors in acidic and basic media

mole (mol)

the amount of a substance that contains 6.02 x 10^23 representative particles of that substance

concentration of a solution

the amount of solute present in a given quantity of solvent or solution

oxidation state

the condition of an atom expressed by the number of electrons that the atom needs to reach its elemental form

qualitative analysis

the determination of the amount or concentration of a substance in a sample

atomic mass

the mass of the atom in atomic mass units (amu)

theoretical yield

the maximum amount of product that can be produced from a given amount of reactant

actual yield

the measured amount of a product obtained from a reaction

when diluting a concentrated solution...

the number of moles remain constant

equivalence point

the point at which the two solutions used in a titration are present in chemically equivalent amounts

hydration

the process in which an ion is surrounded by water molecules

Stoichiometry

the quanitative study of reactants and products in a chemical reaction

percent yield

the ratio of the actual yield to the theoretical yield expressed as a percent

aqueous solution

the solute initially is a liquid or a solid and the solvent is water

mole method

the stoichiometric coefficients in a chemical equation can be interpreted as the number of moles of each substance

molecular weight

the sum of the atomic weights of all the atoms in a molecule