Chem Chapters 4-6
Rules for redox reactions, oxidation states (what is fluorine)
(MEMORIZE THESE) 1. An atom in an element is 0 2. A monatomic ion is the same as its charge (ie Na+, Cl-) 3. Fluorine is -1 in its compounds 4. Oxygen is usuallt -2 in cmpds (exceptions are peroxides- containing O₂²⁻- in which oxygen is -1) 5; Hydrogen is +1 in its covalent compounds (ie H2O, HCl) Assign the ones that have rules first. Remember to solve polyatomics first, then move on to compound overall
percent yield formula
(actual amount/ theoretical amount) X 100
In a certain experiment 28.0 mL of 0.250 M HNO3 and 53.0 mL of 0.320 M KOH are mixed. What is the concentration of H+ or OH- ions in excess after the reaction goes to completion?
0.123 M OH⁻ See page 143 of textbook
Units of pressure
1 atm=760 mmhg=760 torr = 101,325 Pa
You have three 1.0 L flasks at STP. Flask A is He, Flask B is O2, Flask C is H2 1. Which flask particles have the lowest average KE? 2. Which flask has particles w the highest average velocity? Eqs: KEavg= (3/2)RT Urms= √(3RT/M)
1. STP is 1 atm, 25 C or 298 K. All flasks have same volume. Eq is KEavg= (3/2)RT. Therefore since R is a constant and all have same T, all particles have same average KE 2. Use the equation Urms= √(3RT/M) and remember that M is the mass of particles in Kg. So whichever gas has the lowest M will have the highest Urms (average velocity), since M is in the denominator Remember that M is the mass of a mole of particles in Kg Flask C, with helium, would have the lowest M and therefore the highest avg velocity This makes sense- small particles can move faster
Solute electrolyte types
1. Strong electrolytes: soluble salts, strong bases, strong acids 2. Weak electrolytes 3. Nonelectrolytes
Kinetic Molecular Theory (4 postulates- MEMORIZE THESE)
1. Volume of individual particles can be assumed to be 0 2. Particles are in constant motion, collisions of particles with walls of container are cause of pressure exerted by gas 3. No particle interactions in gas 4. Average kinetic energy of gas particles is directly proportional to kelvin temperature of the gas Only for ideal gases (not real)
Sample of N2 has volume of 1.75 L at STP. How many moles N2 are present?
1.75 L * (1 mole N2/ 22.42 L)= 7.81*10⁻² mol N2
What is 1/2mu² the formula for? What is NA1/2mu² the formula for?
1/2mu²= The average kinetic energy of a gas particle NA1/2mu²= average kinetic energy of a mole of gas particles KNOW THIS
Sample of methane having volume 2.80 L at 25 C and 1.65 atm mixed w sample of O2 gas having vol of 35.0 L at 31 C and 1.25 atm. Then ignited to form CO2 and H2O. What is vol of CO2 formed at pressure of 2.50 atm and 125 C
2.47 L See page 181
Molar Volume of an Ideal Gas
22.414 L/mol @ STP (STP is 0C and 1 atm, and molar volume is one mole of a gas)
In a hydrogen fuel cell, hydrogen gas and oxygen gas are combined to form water. Write the balanced chemical equation describing this reaction (using lowest whole-number coefficients).
2H₂+O₂→2H₂O
152 g CaCO3 decomposes in reaction CaCO3 →CaO(s) + CO2(g) What is vol of CO2 produced?
34.1 L CO2 See page 180
A sample of iron ore weighing 0.3500 g was dissoved in acidic soln, all of the iron was reduced to Fe²⁺. Then soln was titrated with 1.621 * 10⁻² M KMnO₄ soln. Required 41.56 mL of permangante soln to reach endpoint. Determine mass percent of iron in the iron ore Unbalanced eq: H⁺ (aq) + MnO₄⁻ (aq) + Fe²⁺ (aq) →Fe³⁺ (aw) +Mn²∙ (aq) +H₂O(l)
53.74% (See page 159 in book)
What volume of 16 M sulfuric acid must be used to prepare 1.5 L of a 0.10 M sulfuric acid soln
9.4*10^-3 L
Most genera definition of acids and bases
Acid is H+ donor, base is H+ acceptor
Key difference between acids and bases
Acids release H+, bases release OH
Acid-base titration
Adding an acid to a base or vice versa until the equivalence point (the point where enough titrant has been added to react exactly with the analyte) has been reached.
In the complicated gas equations, what is u²−
Average of square of gas particle velocities
What is oxidized, what is reduced, what are oxidizing and reducing agents: 2PbO + CO ---> 2Pb + CO2
C went from +2 to +4, lost electons, oxidized Pb went from +2 to 0, gained electrons, reduced Carbon was reducing agent bc it was oxidized Lead was oxidizing agent bc it was reduced
How to write a complete ionic equation? Net ionic equation?
Complete ionic equation: All substances that are strong electrolytes should be written out as dissolved ions (aq) Net ionic equation: Include only the things that are directly involved in the reaction- get rid of any ions that are aqueous on both sides
Effusion vs diffusion
Diffusion describes the mixing of gases. Effusion describes the passage of a gas through a "tiny orfice" into an evacuated chamber
Avogadros law
Direct proportional relationship between volume and moles of gas at constant T and P v=am V1/n1 = V2/n2
_________________can be used to classify solns into strong electrolytes, weak electrolytes, and nonelectrolytes
Electrical conductivity (a substance's ability to conduct an electric current) Strong electrolytes conduct electricity very well; weak electrolytes don't conduct electricity as well. Nonelectrolytes do not conduct current at all
Weak electrolytes
Exhibit a small degree of ionization in water- so they produce only a few ions when dissolved in water. Also therefore weak electrolytes
Balance the redox reaction: Br- + MnO₄⁻ → Br₂ (l) + Mn²⁺ (also show what you would do if it was in basic soln)
Follow the steps, get 16H+ + 2MnO₄⁻ + 10Br⁻ →2Mn²⁺ +8H2O + 5Br₂ If it was in basic soln, you would add 16OH to both sides to get rid of the 16H+ and turn it into H2O 8H2O+ 2MnO₄⁻ + 10Br⁻ →2Mn²⁺+ 5Br₂ +16OH-
Write the formula equation, the complete ionic equation, and the net ionic equation for combining potassium hydroxide with Iron (III) nitrate
Formula eq: 3KOH (aq) + Fe(NO₃)₃ (aq) ---> 3KNO₃ (aq) + Fe(OH)₃ (s) Complete ionic: 3K⁺ (aq) + 3OH⁻ (aq) + Fe³⁺(aq) + 3NO₃⁻ (aq) ----> 3K⁺ (aq) + 3NO₃ (aq) + Fe(OH)₃ (s) Net ionic: 3OH⁻ (aq) + Fe³⁺ (aq) ---->Fe(OH)₃ (s)
The blood alcohol level C2H5OH can be determined by titrating a sample of blood plasma with an acidic potassium dichromate solution, resulting in the production of Cr3+ (aq) and carbon dioxide. The reaction can be monitored because the dichromate ion (Cr2O7 2-) is orange in solution, and the Cr3+ ion is green. The unbalanced redox equation is Cr2O7 2-(aq) + C2H5OH(aq) ⟶ Cr3+(aq) + CO2(g) 1. Balance the equation. 2. If 31.0 mL of 0.0600 M potassium dichromate solution is required to titrate 30.0 g of blood plasma, determine the mass percent of alcohol in the blood (aka blood alcohol content (BAC)). 3. If a person with this BAC were pulled over while driving, would it result in a DUI in US? US legal intoxication limit: BAC of 0.08% or greater
Get 0.143% BAC
You have 1.25 L of 0.0500 M Pb(NO₃)² and 2.00 L of 0.0250 M Na₂SO₄ mixed together What is mass of PbSO₄ forms?
Get moles of each ion 0.0625 moles Pb²⁺ 0.0500 moles SO₄²⁺ Because Pb²⁺ and SO₄²⁺ react in a 1:1 ratio, the amount of SO₄²⁺ will be limiting Then 0.0500 moles SO₄²⁺ will lead to 0.0500 mol PbSO₄, which is 15.2 grams PbSO₄
28.0 mL of 0.250 M HNO3 and 53.0 ml of 0.320 M KOH mix, what is [ ] of H+ or OH- ions in excess after rxn goes to completion?
H+ produces 0.00700 mol H2O OH- produces 0.0170 mol H2O So excess OH- ions 0.0170-0.00700 mol= 0.0100 mol OH- Then need concentration 0.0100 mol OH / (0.0810 L) = 0.123 M OH-
Strong acids (what are they)
HCl - hydrochloric acid, HBr - hydrobromic acid, HI - hydroiodic acid, HNO3 - nitric acid, HClO3 - chloric acid, HClO4 - perchloric acid, H2SO4 - sulfuric acid* Acronym (remember they all start w H): CLimbing BRown Iguanas NOtoriously ClOthe, Courageous (ClO4), SOybeans
Oxidation states (NH4)2HPO4
HPO₄⁻² is a polyatomic O is -2 H is +1 P must be +5 Since (NH4)2 is +2 overall, H = +1 And N must be -3
Difference between weak and strong electrolyte
How much charge goes into the soln
When ions dissolve in water, water creates a _______________
Hydration shell
If the volume of a gas is reduced and temp remains constant, the pressure ___________. If the temperature increases and volume remains constant , the pressure__________. If you increase the moles of particle present, the pressure __________-.
Increases
Redox reaction definition
Involves the transfer of one or more electrons (need to know oxidation states to figure out whether electrons being transferred)
Hydration of ions
Ions dissolve in water
What are the 8 strong bases
LiOH - lithium hydroxide, NaOH - sodium hydroxide, KOH - potassium hydroxide, RbOH - rubidium hydroxide, CsOH - cesium hydroxide, Ca(OH)2 - calcium hydroxide, Sr(OH)2 - strontium hydroxide, Ba(OH)2 - barium hydroxide
Rules for balancing redox reactions
MEMORIZE THESE 1. Write separate equations for the oxidation and reduction half-reactions 2. For each half-reaction: a. Balance all the elements except hydrogen and oxygen b. Balance oxygen using H2O c. Balance hydrogen using H+ d. Balance the charge using electrons 3. If necessary, multiply one or both balanced half-reactions by an integer to equalize the number of electrons transferred in the two half-reactions 4. Add the half-reactions, and cancel identical species 5. Check that the elements and charges are balanced Also if it's in basic solnthen at step 4 get rid of any H+ ions by adding OH- to both sides; then the H⁺ + OH becomes H2O
In the complicated gas equations, what is m
Mass IN KG!!! (NOT GRAMS)
Oxidation states KMnO4
MnO4- is polyatomic O is k-2, so Mn is +7 Since MnO4 is -1, K is +1
Density of a gas was 1.95 g/L at 1.50 atm and 27 C. What is molar mass?
Molar mass= dRT / P 32.0 g/mol See page 183
Dilution
Moles of solute before dilution= moles of solute after dilution When water is added to a stock solution to achieve a reduced molairity
What is the precipitate in the reaction of sodium hydroxide and hydrochloric acid?
NaOH (aq) +HCl (aq)→ H₂O (l) + NaCl (aq) WATER is the precipitate. Water is not aqueous. It IS the solvent so it can't be.
You have 0.1 L of 0.1 M BaCl₂, reacts with 0.1 L of 0.1 M Fe₂(SO₄)₃, what mass BaSO₄ is made?
Net ionic: 3 Ba²⁺ + 1 SO₄²⁻ → 3BaSO₄ 0.100 L Ba²⁺ * ( 0.100 mol/ 1 L) * (3 BaSO₄/ 3 Ba²⁺) * (233.4 G / 1mol) = 2.33 g 0.100 L SO₄² * ( 0.100 mol/ 1 L) * (3 BaSO₄/ 1 SO₄²) * (233.4 G / 1mol) = 7 g So 2.33 g produced, Ba is limiting reactant
Would 1 mole of O2 gas exert a different pressure (at same temp and volume) than 1 mole N2 gas?
No- identities of gases don't matter; just how many moles of gas are present
Oxidation states C6H12H6
O is -2 H is +1 C must be 0
Oxidation states Na4Fe(OH)6
O is -2 H is +1 Na is +4 Therefore, +4 - 6 + Fe = 0 So Fe must be +2
What are oxidation and reduction, and what are the oxidizing and reducing agents
Oxidation: increase in oxidation state (loses electrons, becomes more positive) Oxidizing agent: thing that is reduced (more positive, less negative) Reduction: Decrease in oxidation state (gains electrons) Reducing agent: thing that is oxidized (loses electrons, less negative, more positive)
Oxidation states KH2PO4
Oxygen is -2 K is +1 H is +1 PO₄³⁻ is polyatomic, P is +5 (since O is -2 each, and the overall charge is -3. -8+5=-3)
Mole fraction of nitrogen is 0.7808. Calculate the partial pressure of N2 in air when atmospheric pressure is 760. torr
P1 = X1 *P total 593 torr
Ideal gas law
PV=nRT R is 8.206 * 10⁻² (L*atm)/(k*mol)
2KClO3 (s) ---> 2 KCl (s)+ 3O2 (g) Oxygen produced was collected by displacement of water at 22 C at total pressure 754 torr. Vol gas collected was 0.650 L, vapor pressure of water is 21 torr at 22C. Calculate the partial pressure of O2 in the gas collected and the mass KClO3 in the original sample
Partial pressure of O2: 0.964 atm Mass KClO3 in the original sample: 2.12 g See page 188
What is effusion and how does it relate to mass of particles
Passage of gas through small hole into empty chamber. Rate of effusion is inversely proportional to square root of molar mass of particles, meaning that small particles effuse faster than larger ones
What kind of bond holds water together and why is this important
Polar covalent, meaning that electrons are shared, but unequally. Important bc it means all polar substances dissolve in water (especially strong acids, bases, salts)
Three types of solution reactions
Precipitation, acid-base, oxidation-reduction
Boyle's law
Pressure and volume have an inverse relationship when T is constant and the amount of gas is constant PV=k P is proportional to 1/V Therefore, P1V1=P2V2
Daltons Law of Partial Pressures
Ptotal = P1 + P2 + P3 And since Molar mass= nRT /V, Ptotal =(n1RT /V) + (n2RT /V) ... If all of the gases in the mixture are at the same temp and volume (which they would be) can make it Ptotal = (n1 + n2 + n3...)(RT/V)
Mole fraction definition and equation
Ratio of the number of moles of a given component in a mixture to the total number of moles in the mixture X1 = n1/ntotal Since n= p(v/RT) can also be calculated if given the pressure of a gas and the total pressures, and the temperature and volume are constant X1 = P1/Ptotal Remember- can also be rearranged to be P1 = X1 *P total
What is oxidized, what is reduced, what are oxidizing and reducing agents: 2PbS + 3O2 ---> 2PbO + 2SO2
Reactants: -O is 0 -Pb is +2 - S is -2 Products: -O is -2 -S is +4 -Pb is +2 S went from -2 to +4 so lost electrons, was oxidized Oxygen went from 0 to -2, gained electrons, was reduced Oxygen is oxidizing agent bc it was reduced Sulfur was reducing agent bc it was oxidized
Is NH4NO3 an acid or a base
Salt, according to the chem hw
2KClO₃ (s) → 2KCl (s) + 3O₂(g) Oxygen collected by displacement of H₂O at 22C at total pressure 754 torr, vol gas collected at 0.650 L, vapor pressure of H₂O is 21 torr at 22C. Calculate partial pressures of O2 in gas, mass of original KClO₃
See notes PO2 = 754 total torr- 21 torr water vapor= 733 torr Moles O2= 0.0259 using PV=nRT and P= (733 torr O2/ 760)= 0.964 atm Mass KClO₃= 2.11 g (use stoichiometry)
What volume of a 0.100 M HCl solution is needed to neutralize 25.0 mL of 0.350 M NaOH
See page 142 of textbook. 8.75 *10⁻² L
Titration- student weight out 1.3009 g sample of potassium hydrogen pthalate, dissolves it in water. KHP has one acidic hydrogen. Titrates soln with sodium hydroxide. The difference between the final and initial NaOH readings on the buret is 41.20 mL. Calculate the [] of the NaOH soln
See page 145 in book. Should get 0.1546 M
Balance H+ (aq) + Cr₂O₇²⁻ (aq) + C₂H₅OH (l) → Cr³⁺ (aq) + CO₂ (g) +H₂O (l)
See page 155 in book Should get 16H+ (aq) + 2Cr₂O₇²⁻ (aq) + C₂H₅OH (l) → 4Cr³⁺ (aq) + 2CO₂ (g) + 11H₂O (l)
Balance Ag (s) + CN⁻ (aq) + O₂ (g) →Ag(CN)₂⁻ (aq) Occurs in basic sokn
See page 157 of book 4Ag (s) + 8CN⁻ (aq) + O₂ (g) + 2H₂O (l)→Ag(CN)₂⁻ (aq) + 4OH⁻ (aq)
Gas has pressure of 345 torr at temp of -15 C and volume of 3.48 L, if conditions change so that temp is 36 C and pressure is 468 torr, what is new volume
See page 177 3.07 L
46 L He at 25 C and 1 atm and 12 L O2 at 25 C and 1 atm were pumped into a scuba tank w a volume of 5.0 L. Calculate the partial pressure of each gas and total pressure in tank at 25 C
See page 184 pHe= 9.3 atm pO2= 2.4 atm Total pressure: 11.7 atm
How do you find molar mass of a gas given density and some other stuff
So PV=nRT And then n, the number of moles, is (mass of sample)/(molar mass) So P= nRT / V or P= ([(mass of sample)/(molar mass)]RT ) / V P= (mass of sample*RT)/ (V*molar mass) And then (mass of sample) /V = density of gas So P= (dRT)/ molar mass Therefore Molar mass= dRT / P
Solute vs. Solvent
Solute : What is dissolved in a solution(salt) Solvent : What dissolves the solute(water)
Base definition
Solute that can give up hydroxide ion into the soln (OH); proton acceptor
*strong electolytes
Substances that are completely ionized when they are dissolved in water. Includes soluble salts, strong acids, and strong bases.
Nonelectrolytes
Substances that do not produce any electrolytes when dissolved in water, and resulting soln therefore does not conduct electric current
Oxidation state definition
The imaginary charges the atoms would have if the shared electrons were divided equally between identical atoms
Formula is Urms= √3RT/M. What is formula for? What are the units for your answer and what do the variables mean?
Urms= √3RT/M Formula for root mean square velocity (average velocity of particles) M here is NOT molarity- it is the mass of a mole of the gas in Kg- so the molar mass of the element/compound in kilograms (equal to Na * m) Units are m/s A smaller M in this equation leads to a bigger Urms. This makes sense- a smaller particle would have a higher velocity (think of Ms. Packard's analogy of how "smaller"/more skinny people can run faster) NEED TO KNOW THIS
If the absolute temperature of a gas is doubled, what happens to the root-mean-square speed of the molecules?
Urms= √3RT/M So if T went from 2K to 4K, Urms would go from √2 to 2 So new speed is 1.414 times original
Sample of gas at 15 C and 1 atm has volume of 2.58 L. What volume will gas occupy at 38C and 1 atm?
Use Charles' law, V1/T1=V2/T2 Remember to change to K Get 2.79 L
12.2 L sample has 0.50 moles oxygen gas at pressure of 1 atm and temp of 25 C. If all of this O2 were converted to O3 at the same temp and pressure what would be the volume of the O3
Use avogadro's law, V1/n1 = V2/n2 Get 8.1 L
1.53 L sample of gaseous SO2 at pressure of 5.6 * 10³ Pa; pressure is changed to 1.5 * 10⁴ Pa at a constant temp, what is new volume?
Use boyle's law, P1V1=P2V2 Get 0.57 L
Charles' law
Volume and temp have a direct propotional relationship The experiments that discovered this are also the reason we know about absolute 0 V=bt Or V1/T1=V2/T2
When collecting a gas over water you need to remember to include __________ in any gas calculations
Water vapor pressure-will contribute to total pressure along with any other gases that were collected over water
*hydration
When an ionic substance dissolves in water and the "positive ends" of the water molecules are attached to the negative anions, and the "negative ends" of the water molecules are attracted to the positive cations
Precipitation reaction
When two solutions are mixed and an insoluble substance forms. Use solubility rules to determine which product is the solid or liquid precipitate
Partial pressure of oxygen was 156 torr in air with total atmospheric pressure 743 torr. Calculate mole fraction of O2 present
X1 = P1/Ptotal 156 torr/ 743 torr= 0.210
Can there be noninteger oxidation states? If so, what does that mean?
Yes. Means that the element has multiple oxidation states which average out to a noninteger number. For example Fe3O4
What do you need to remember about the stoichiometry of precipitation reactions?
You need to remember to determine which reactant is limiting!
Identify the oxidized substance, the reduced substance, the oxidizing agent, and the reducing agent in the following redox reaction: Zn + Cu²⁺ →Zn²⁺ + Cu
Zn + Cu²⁺ →Zn²⁺ + Cu Oxidized: Zn Reduced: Cu²⁺ (NOT Cu- must be one of the reactants)
strong acid/base definition
completely ionizes in an aqueous solution, strong electrolyte
weak acids and bases
do not completely dissociate in solution
The hydroxide ion is a very strong base, meaning that
it will react completely with any weak acids it's combined with
Equation for molar mass of an ideal gas (memorize this!!)
mm= (dRT) / P
Molarity
moles solute / liters soln
2H₂+O₂ →2H₂O 1 atm, 1.70*10⁸ L H₂, 25 C How much H₂O (in grams) made?
n = [(1 atm)(1.7*10⁸L)]/[(0.08206)(25+273)]= moles H2 Remember- temp at ATP is 0 C or 273 K Then do stoich to find grams H₂O
Acid-base reactions are also called ___________ reactions.
neutralization
Acid definition
proton donor Creates H3O+ (Hydronium) because when the proton dissociates it goes onto water
Strong electrolytes
substances that completely dissociate into ions when they dissolve in water tons of charge inside soln 100% of solute in ionic form
If you are presented with an acid or base that is not on the strong list, means_______
that means that acid or base is weak
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
In aqueous solutions, ________ is the _________
water is the solvent
