Honors Chemistry

Answers to Chapter 3 Study Questions

1.  a)  3(12.0) + 8(1.01) + 3(16.0)  =  92.1 g/mole         b)  92.1 g        c)  6.02 x 1023 molecules

d) =  20.0 g

2.  a)  4 atoms (one N + 3 H)

b) =  2.41 x 1024 atoms

c) =  4.82 x 1023 atoms

3.  Molar mass of NaNO2 = 23.0 + 14.0 + 2(16.0)  =  69.0 g/mole

% Na = 23.0/69.0 = 33.3% Na;  % N = 14.0/69.0 = 20.3% N;  %O = 2(16.0)/69.0 = 46.4% O

33.3% Na, 20.3% N and 46.4% O.

4.  a)  In 100 g of this compound, there are 40.7 g C, 5.1 g H, and 54.2 g O =  3.39 moles C                   3.39/3.39  =   1    x 2   =   2 =  5.1 moles H                     5.1/3.39    =  1.5  x 2   =   3 =  3.39 moles O                   3.39/3.39  =   1    x 2   =   2

empirical formula  =  C2H3O2

b)  Molar mass of C2H3O2  =  2(12.0) + 3(1.0) + 2(16.0)   =  59.0 g/mole

118/59.0  =  2  ®  molecular formula  = C4H6O4

5.  a)  In 25.0 g of compound, there are 7.20 g Mg, 3.55 g C and 25.0-(7.20+3.55) = 14.25 g O. =  0.296 moles Mg           0.296/0.296  =  1 =  0.296 moles C                    0.296/0.296  =  1 =  0.891 moles O                0.891/0.296  =  3

formula  =  MgCO3

b)  % Mg = 7.20/25.0 = 28.8% Mg;  %C = 3.55/25.0 = 14.2 % C;  % O = 14.25/25.0 = 57.0% O.  (You should get the same result using molar mass and atomic masses.)

c) =  4.00 g Mg

5.  d) =  24.5 g compound

6.  mass of Zn  =  33.64 g  - 32.00 g   =  1.64 g Zn

mass of O  =  34.04 g  -  33.64 g  =   0.40 g O.

# moles Zn: =  0.0251  moles Zn           0.251/0.25  =  1

# moles O: =  0.025  moles O                   0.25/0.25  =  1

formula   =   ZnO

7.  a)   B2H6(l)  +   3  O2(g)    ®     B2O3(s)  +   3  H2O(l)

b)   4  PH3(g)  +   8  O2(g)     ®    6  H2O(l)  +    P4O10(s)

8.    a)   6 Li(s)   +    N2(g)    ®    2  Li3N(s)

b)   Co(NO­­3)3(aq)    +    3  NaOH(aq)    ®    3  NaNO­­3(aq)    +    Co(OH)3 (s)

c)    Zn(s)    +    2  HCl(aq)    ®    ZnCl2(aq)    +    H2(g)

d)  (a)  is a combination (synthesis) reaction.  (b) is a double replacement reaction.

9.  a) =   8.20 moles H2S

b) =   48.0 g O2

c) =   3.60 g H2O

d) = 15.0 g SO2 =  80.0%

e) =  5.00 g SO2 =   4.01 g SO2

O2 is limiting;  4.01 g SO2 is produced

10.  a)   H2(g)   +   Cl2(g)    ®    2 HCl(g)

b)  H2 is limiting (H2 and Cl2 react in a ratio 1:1 ratio and there is less H2.)

c) =  15.0 mol HCl

d)  9.00  - 7.50  =  1.50 mol Cl2 left