Download Extra Unit 3 Problems for the Web Site (Honors

Extra Unit 3 Problems for the Web Site (Honors &
Regents): The Mole, Chemical Equations and
Stoichiometry.
[Note that the questions marked (R) on the Unit 2 web page are relevant to Honors
students in this unit)
1. Balance the following equations: (a) Ag2O ---> Ag + O2 (b) Zn + HCl ---> ZnCl2 + H2
(c) NaOH + H2SO4 ---> Na2SO4 + H2O
2. Upon the addition of heat to an unknown amount of potassium chlorate, 0.96 g of
oxygen was liberated. How much potassium chlorate was present? (The other product
was potassium chloride).
3. Given the balanced equation
4NH3 + 5 O2 ---> 4NO + 6H2O
How many grams of ammonia will be required to react with 80. g of O2?
4. In the commercial preparation of hydrogen chloride gas, what mass of HCl in grams
may be obtained by heating 234 g of NaCl with excess H2SO4? The balanced equation for
the reaction is
2NaCl + H2SO4 ---> Na2SO4 + 2HCl
5. A chemist decides to react 2.0 g of VO (vanadium oxide) with 5.75 g of Fe2O3 to
produce V2O5 and FeO. How many grams of V2O5 can be obtained?
6. Calculate the volume of O2 necessary to burn 50. L of CO completely. The balanced
equation is:
2CO + O2 ---> 2CO2
Also, calculate the volume of CO2 formed.
7. Chlorine may be made by the action of KClO3 with HCl, and the reaction may be
represented by the equation:
KClO3 + 6HCl ---> 3Cl2 + 3H2O
Calculate the mass of KClO3 which would be required to produce 1.0 L of chlorine gas at
STP.
8. The executioner in charge of the lethal gas chamber at the state penitentiary adds
excess dilute H2SO4 to 196 g of NaCN. What volume of HCN gas is formed at STP?
H2SO4 + 2NaCN ---> 2HCN + Na2SO4
The following problems are for Honors only:
9. When 4.90 g of KClO3 was heated, it showed a mass loss of 0.384 g. Find the percent
of the original KClO3 that had decomposed.
10. When 10.0 g of silicon dust, Si, is exploded with 100.0 g of oxygen, O2, forming
silicon dioxide, SiO2, how many grams of O2 remain uncombined? The reaction equation
is
Si + O2 ---> SiO2
11. What is the maximum mass of SO3 that could be made from 25.0 g of SO2 and 6.00 g
of O2 by the following reaction?
2SO2 + O2 ---> 2SO2
12. A given sample of pure compound contains 9.81 g of zinc, 1.8 x 1023 atoms of
chromium, and 1.05 mole of oxygen atoms. What is the empirical formula?
13. Of the total number of atoms in the universe, approximately 93% are hydrogen, and
7% are helium. What percentage of the universe by mass is hydrogen?
Answers: 1. [2,4,1; 1,2,1,1; 2,1,1,2] ; 2. [2.5g]; 3. [34g]; 4. [146g]; 5. [2.18g]; 6. [25 L;
50. L]; 7. [1.84g]; 8. [89.6 L]; 9. [20.%]; 10. [88.5g]; 11. [30.1g]; 12. [ZnCr2O7]; 13.
[77%]
The following is an example of an Honors test for Unit 3:
1. All of the following are clues that a chemical reaction must have taken place except:
a) a color change b) a solid forms c) bubbles form d) the reactant gets smaller e) a flame
is produced
2. In a chemical reaction, which of the following must remain unchanged?
a) temperature b) number of atoms c) phase d) number of molecules
3. When the equation: Fe2(SO4)3(aq) + Ba(OH)2(aq) ------> is completed and balanced, a
term in the balanced equation is:
a) Ba2(SO4)3(aq) b) 2Fe(OH)3(s) c) 2Fe(OH)2(s) d) 2Fe2(SO4)3(aq)
4. If a synthesis reaction takes place between potassium and bromine, what is the
product?
a) PbBr2 b) PBr3 c) KBr2 d) KBr
5. The reaction 2K(s) + 2H2O(l) ----> 2KOH(aq) + H2(g) is classified as what type of
reaction?
a) synthesis b) single replacement c) decomposition d) double replacement
6. Choose the false ststement.
a) 1 mole = 6.02 x 1023 amu b) 1 mole of atoms = 6.02 x 1023 atoms c) 6.02 x 1023
hydrogen atoms weighs 1.008 g
d) 1 mole of carbon - 12 atoms weighs 12.00 g e) 1 mole of fluorine gas contains 1.204 x
1024 fluorine atoms
7. The gram formula mass of Ba(NO3)2 is
a) 199.2 g/mol b) 261.3 g/mol c) 247.3 g/mol d) 167.3 g/mol e) none of these
8. Which of the following contains the smallest number of molecules?
a) 5.0 g CO2 b) 5.0 g O2 c) 5.0 g N2 d) 5.0 g H2O
9. The percentage composition (by mass) of Mg3N2 is
a) 72.2% Mg, 27.8% N b) 63.4% Mg, 36.6% N c) 83.9% Mg, 16.1% N d) none of these
choices
10. Which of the following has the largest percent by mass of carbon?
a) CaCO3 b) CO2 c) CH4 d) NaHCO3
11. A sample of metal with a mass of 2.51 g is combined with oxygen; the metal oxide
weighs 3.01 g. The mass percent of oxygen in the compound is
a) 19.9% b) 16.6% c) 83.4% d) 50.0% e) cannot be determined from the information
given
12. Choose the pair of compounds with the same empirical formula.
a) C2H2 and C6H6 b) NaHCO3 and Na2CO3 c) K2CrO4 and K2Cr2O7 d) H2O and H2O2
13. What mass of oxygen would be required to completely burn 6.75 g of propane in the
reaction:
C3H8(g) + 5 O2(g) ----> 3CO2(g) + 4H2O(g)
a) 33.8 g b) 49.0 g c) 24.5 g d) 122g
14. A compound is analyzed and found to contain 12.1% carbon, 16.2% oxygen, and
71.7% chlorine. What is the empirical formula of this compound?
a) COCl b) COCl2 c) CO2Cl d) CO2Cl2 e) COCl4
15. A certain compound has an empirical formula of NH2O. Its molar mass was
experimentally determined to be between 60 and 65 g/mol. Its molecular formula is
a) NH2O b) N2H2O2 c) N2H4O2 d) none of these
16. Consider the reaction: Mg2Si(s) + 4H2O(l) ----> 2Mg(OH)2(aq) + SiH4(g)
Which of the reactants is in excess if we start with 50.0 g of each reactant?
a) Mg2Si b) H2O c) Mg(OH)2 d) SiH4
17. Sodium and water react according to the following reaction: 2Na(s) + 2H2O(l) ---->
2NaOH(aq) + H2(g)
How many moles of hydrogen will be produced when 4 moles of sodium react with 2
moles of water?
a) 1 b) 2 c) 3 d) 4 e) none of these
18 and 19. Consider the reaction: N2(g) + 3H2(g) ----> 2NH3(g)
18. How many liters of ammonia will be produced from 2.0 moles of hydrogen and
excess nitrogen?
a) 2.0 L b) 29.9 L c) 44.8 L d) 1.3 L
19. When ammonia is prepared from 28.0 g nitrogen and excess hydrogen, 30. g of
ammonia are produced. What is the percentage yield?
a) 6% b) 12% c) 82% d) 88% e) 30%
20 and 21. Refer to the following equation: 4NH3(g) + 7 O2(g) ----> 4NO2(g) + 6H2O(g)
20. How many liters of ammonia will be required to produce 10.0 L of water?
a) 4.00 L b) 10.0 L c) 6.67 L d) 5.00 L
21. How many molecules of NO2 are produced when 1 mole of ammonia is completely
reacted?
a) 4 b) 12.04 x 1023 c) 6.02 x 1023 d) 46
22. Which of the following metals will not react with hydrochloric acid to release
hydrogen gas?
a) zinc b) magnesium c) silver d) tin
23. A compound is analyzed and found to contain 40.0% carbon, 6.7% hydrogen, and
53.3% oxygen. If the molecular mass of compound is 60.0 g/mol, what is the molecular
formula?
24. In an oxy-acetylene torch the following reaction occurs: 2C2H2(g) + 5 O2(g) ---->
4CO2(g) + 2H2O(l)
How much acetylene must be used to produce 18.0 g of carbon dioxide if this reaction
has an 85.0% yield?
25. Balance the following equations and identify the type of reaction as synthesis,
combustion, single replacement, double replacement, or decomposition(analysis).
a) Na2SO4(aq) + Pb(NO3)2(aq) ----> PbSO4(s) + NaNO3(aq)
____________________________
b) Cl2(g) + AlBr3(aq) ----> AlCl3(aq) + Br2(l)
_________________________________________
c) C6H14(l) + O2(g) ----> CO2(g) + H2O(l)
_____________________________________________
d) Mg(NO3)2(s) ----> MgO(s) + NO2(g) + O2(g)
________________________________________
26. Consider the reaction: 2CH4(g) + 3 O2(g) + 2NH3(g) ----> 2HCN(g) + 6H2O(g)
a) if 128 g NH3 is reacted with an equal amount of CH4 in excess oxygen, what is the
mass of HCN produced?
b) how many grams of the excess reagent will remain along with the excess oxygen?
c) if the percent yield from this reaction is only 64.0%, how much HCN was obtained as
a product?
27. Write a complete and balanced chemical equation for each of the following sets of
reactants: (if no reaction occurs, write N.R.)
a) aqueous sodium phosphate + hydrochloric acid b) zinc metal + nitric acid c) copper +
sulfuric acid
Answers: 1 d, 2 b, 3 b, 4 d, 5 b, 6 a, 7 b, 8 a, 9 a, 10 c, 11 b, 12 a, 13 c, 14 b,
15 c, 16 b, 17 a, 18 b, 19 d, 20 c, 21 c, 22 c.
23) C2H4O2. 24) 6.26 g acetylene. 25)a. 1,1,1,2 D.R. b) 3,2,2,3 S.R. c)
2,19,12,14 Combustion d) 2,2,4,2 analysis. 26) a. 203 g HCN b) 7.52 g CH4
in excess c) 130. g HCN produced. 27 a) Na3PO4(aq) + 3HCl(aq) ----> N.R.
b) Zn(s) + 2HNO3(aq) ----> Zn(NO3)2(aq) + H2(g) c) N.R.