Unit 1 Problem Set
AP Chemistry
Name: ____________________________ #______
Block: __________
Section 1: Mass Spectrometry and Average Atomic Mass
1. Given the following data, calculate the average atomic mass of neon.
Isotope
20
Ne
21
Ne
22
Ne
% Abundance
90.48
0.27
9.25
2. Answer the next 3 questions given the following mass spectra:
2a. Based on the mass spectrum of atom Y, which of the following statements is false?
a. peak A and peak D come from atoms that have the same number of electrons
b. there are seven isotopes of atom Y
c. peak C comes from the most abundant isotope of atom Y
d. peak D comes from an atom with 4 more protons than the atom that gave peak B
2b. The identity of compound Y is:
a. zirconium
c. americium
b. molybdenum
d. einsteinium
2c. Which peak comes from an atom with the greatest number of neutrons?
a. A
c. C
b. all peaks in the spectrum have
d. D
the same number of neutrons
3. Given the mass spectrum, determine the average atomic mass of lithium.
93
7
4. Sketch the mass spectrum given the following data:
Section 2: Molar Mass and Percent Composition
5. What is the percent by mass of the anion in lithium periodate, LiIO4?
6. What is the molar mass of oxalic acid?
7. A chemist has found 2.0 moles of a mysterious compound contained 48g of carbon, 8g of hydrogen, and
64g of oxygen. What is the molecular formula of the compound?
Section 3: Combustion Analysis
8. A 1.50 g sample of hydrocarbon undergoes complete combustion to produce 4.40 g of CO2 and 2.70 g of
H2O. What is the empirical formula of this compound?
9. A 0.2500 g sample of a compound known to contain carbon, hydrogen and oxygen undergoes complete
combustion to produce 0.3664 g of CO2 and 0.1500 g of H2O. What is the empirical formula of this
compound?
10. Quinone, which is used in the dye industry and in photography, is an organic compound containing only C,
H, and O. What is the empirical formula of the compound if you find that 0.105 g of the compound gives
0.257 g of CO2 and 0.0350 g of H2O when burned completely? Given a molecular weight of approximately
108 g/mol, what is its molecular formula?
11. A carbohydrate is a compound composed solely of carbon, hydrogen and oxygen. When 10.7695 g of an
unknown carbohydrate (MW = 128.2080 g/mol) was subjected to combustion analysis with excess oxygen,
it produced 29.5747 g CO2 and 12.1068 g H2O. What is its molecular formula?
Section 4: Gravimetric Analysis
12. In an experiment, a student is given 2.94g of a mixture containing anhydrous MgCl2 and KNO3. To
determine the percentage by mass of MgCl2 in the mixture, the student uses excess AgNO2(aq) to precipitate
the chloride ion as AgCl(s). The student determines the mass of the AgCl precipitate to be 5.48 g. On the
basis of this information, calculate each of the following.
a. The number of moles of MgCl2 in the original mixture
b. The percent by mass of MgCl2 in the original mixture
13. You dissolve 0.4500 g of impure potassium chloride in water and add an excess of silver nitrate. You get
0.8402 g of insoluble silver chloride. Calculate the percent by mass of KCl in the original sample.
14. A .9157 g mixture of calcium bromide and sodium bromide is dissolved in water and silver nitrate is added
to the solution. If the mass of the precipitate formed is 1.6930g, what is the % by mass of sodium bromide in
the original mixture?
Section 5: Stoichiometry
15. A 10.0 g sample containing calcium carbonate and an inert material was placed in excess hydrochloric acid.
A reaction occurred producing calcium chloride, water, and carbon dioxide.
(a) Write a balanced equation for the reaction.
(b) When the reaction was complete, 1.55 g of carbon dioxide gas was collected. How many moles of
calcium carbonate were consumed in the reaction?
(c) If all the calcium carbonate initially present in the sample was consumed in the reaction, what percent by
mass of the sample was due to calcium carbonate?
(d) If the inert material was only silicon dioxide, what was the mole fraction of silicon dioxide in the
mixture?
(e) In fact, perhaps there had been some other material present in the original sample that was not so inert
and generated a gas during the reaction. Would this have caused the calculated percentage of calcium
carbonate in the sample to be higher, lower or have no effect? Justify your response.
Section 6: Solutions, Concentration, and Dilution
16. Typical blood serum is about 0.14 M NaC1. What volume of blood contains 1.0 mg NaC1?
17. Calculate the mass of solid NaC1 that must be added to 1.50 L of a 0.100 M AgNO3 solution to precipitate
all the Ag+ ions in the form of AgC1.
18. To analyze the alcohol content of a certain wine, a chemist needs 1.00L of an aqueous 0.200 M K2Cr2O7
(potassium dichromate) solution. How much solid K2Cr2O7 must be weighed out to make this solution?
19. What volume of 16 M sulfuric acid is needed to prepare 1.5 L of a 0.10 M H2SO4 solution?
Section 7: Solubility and Net Ionic Equations
20. Using the solubility rules, predict if a reaction will occur. If a precipitate forms, identify the compound.
a. KNO3 (aq) and BaCl2 (aq)
b. Na2SO4 (aq) and Pb(NO3)2 (aq)
c. KOH(aq) and Fe(NO3)3 (aq)
21. For each of the following reactions, write the molecular equation, the complete ionic equation, and the
net ionic equation.
a. Aqueous potassium chloride is added to aqueous silver nitrate to form a silver chloride precipitate plus
aqueous potassium nitrate.
M:
CI:
NI:
b. Aqueous potassium hydroxide is mixed with aqueous iron(III) nitrate to form a precipitate of iron(III)
hydroxide and aqueous potassium nitrate.
M:
CI:
NI:
Section 8: Acids/Bases and Titrations
22. What volume of a 0.100 M HC1 solution is needed to neutralize 25.0 mL of 0.350 M NaOH?
23. In a certain experiment, 28.0 mL of 0.250 M HNO3 and 53.0 mL of 0.320 M KOH are mixed. Calculate the
amount of water formed in the resulting reaction. What is the concentration of H+ and OH- ions in excess
after the reaction goes to completion?
24. A student carries out an experiment to standardize (determine the exact concentration of) a sodium
hydroxide solution. To do this the student weighs out a 1.3009-g sample of potassium hydrogen phthalate
(KHC8H4O4, often abbreviated KHP). KHP (molar mass 204.22 g/mol) has one acidic hydrogen. The
student dissolves the KHP in distilled water, adds phenolphthalein as an indicator, and titrates the resulting
solution with the sodium hydroxide solution to the phenolphthalein endpoint. The difference between the
final and initial buret readings indicates that 41.20 mL of the sodium hydroxide solution is required to react
exactly with the 1.3009 g KHP. Calculate the concentration of the sodium hydroxide solution.
Section 9: Redox Reactions
25. Balance the following redox reactions in acidic solution:
a. Mn2+ + BiO3-  MnO4 + Bi3+
b. ClO3- + Cl-  Cl2 + ClO2
c. P + Cu2+  Cu + H2PO4-
d. PH3 + I2  H3PO2- + I-
e. NO2  NO3- + NO
26. Balance the following redox reactions in basic solution:
a. MnO4- + C2O42-  MnO2 + CO2
b. Cu(NH3)42+ + S2O42-  SO32- + Cu + NH3
c. Zn + NO3-  Zn(OH)42- + NH3
d. Al + OH-  AlO2- + H2