help in Chemistry

1. If a single molecule of a substance weighs 7.64 x 10-23 g, what is its molar mass?

2. Which of the following contains the smallest number of molecules?

A. 1.0 g H2O

B. 1.0 g NH3

C. 1.0 g H2

D. 1.0 g O2

E. all of the above are the same

3. Ethanol (C2H5OH) has a density of 0.789 g/mL. How many ethanol molecules

are in a teaspoon (~ 5 mL) of ethanol?

4. 1023 atoms of zinc weigh nearly the same as:

A. a mole of zinc (Zn).

B. a half of a mole of carbon (C).

C. two moles of xenon (Xe).

D. a mole of boron (B).

174 CHAPTER 5 HOW CHEMISTS MEASURE ATOMS AND MOLECULES

5. In your own words describe what the atomic weight of an element means.

6. What is the molar mass of C3H5(NO3)3?

7. How many moles of ammonia are in 61 g of NH3?

8. Create a solution map for calculating how many hydrogen atoms are present in a

75-g sample of CH3CH2OH and then make this calculation.

9. What mass of N2O contains 0.50 mol of nitrogen atoms?

10. A 1979 penny is 95.05% copper by mass. If the penny weighs 3.098 g, how many

copper atoms does the penny contain?

11. What is the mass percent of oxygen in K2SO4?

12. A substance was analyzed and found to contain only sulfur and fluorine. If there

was 0.1570 g fluorine present in a 0.2011-g sample of this substance, what is the

mass percent composition of this material?

13. How many moles of HNO3 does a 60.0-g sample of a nitric acid solution that is

70.4% HNO3 (by mass) contain?

14. How many grams of Fe2O3 contain 15.0 g of iron?

CHAPTER 5 HOW CHEMISTS MEASURE ATOMS AND MOLECULES 175

15. The balanced equation 2Cu(s) + O2(g) ÷ 2CuO(s) tells us that 1 mol of Cu

A. reacts with 1 mol O2.

B. produces 1 mol CuO.

C. reacts with 32 g of O2.

D. produces 2 mol CuO.

E. does both A and C.

16. Create a solution map for calculating the mass (in grams) of ammonia that can be

produced from 5 kg of hydrogen gas and an excess of nitrogen according to the

reaction N2(g) + 3H2(g) ÷ 2NH3(g).

17. According to the reaction 4Li(s) + O2(g) ÷ 2Li2O(s), how many grams of

Li2O can be produced from each gram of lithium that reacts?

18. The unbalanced equation for the reaction of Na2O2 with water is:

Na2O2 + H2O ÷ NaOH + O2

What mass of oxygen gas will be produced if 3.25 g of sodium peroxide reacts

with a large excess of water?

19. What mass of O2 is needed to react completely with 4.20 g CH4 in a combustion

reaction?

20. How many grams of oxygen gas can be formed from the decomposition of 0.437

mol HgO?

21. For the reaction 2CH4(g) + 3O2(g) + 2NH3(g) ÷ 2HCN(g) + 6H2O(g),

if you start with 5.0 g of each reactant, which substance is the limiting reactant?

176 CHAPTER 5 HOW CHEMISTS MEASURE ATOMS AND MOLECULES

22. How many moles of NH3 can be produced from the reaction of 4.00 mol N2 and

10.0 mol H2?

23. For the reaction CaCO3(s) + 2HCl(aq) ÷ CaCl2(aq) + CO2(g) + H2O(l),

how many grams of CO2 can be produced if 68.1 g CaCO3 (molar mass =100.09

g/mol) is mixed with 51.6 g HCl (molar mass =36.46 g/mol)?

24. How does the actual yield of a chemical reaction compare to the theoretical yield

of the reaction?

25. The unbalanced equation below describes the formation of C2H2.

CaC2(s) + H2O(l) ÷ Ca(OH)2(s) + C2H2(g)

What is the maximum number of grams of C2H2 that can be produced if 8.00 g of

CaC2 and 8.00 g of H2O are allowed to react?

26. When 2.34 grams of aluminum reacts with 1.50 grams of hydrochloric acid,

which reactant is in excess? How much of this reactant is left over?