4. Which of the following has the greatest mass?
1.0 mol zinc
1.0 mol copper
1.0 mol potassium
1.0 mol sulfur
all have the same mass

5. How many mol of CO2 are in 3.3 g of carbon dioxide?
(a) mol (b) mol (c) 150 mol
(d) 13 mol (e) none of the above

6. How many mol of CO2 are in 3.3 g of carbon dioxide?
MOLE
(mol)‏
Mass
(g)‏
Particles
(atoms, fu or mc’s)‏
Molar
AVOGADRO’S
NUMBER ( )‏
1 mol CO2
3.3 g CO2
= mol CO2
44.01 g CO2
How many mol of CO2 are in 3.3 g of carbon dioxide?

7. How many grams of uranium are in 5.00 X 1022 atoms of pure uranium?
(a) 19.8 g (b) g (c) g
(d) 1.19 x 1025 g (e) none of the above

8. ( )‏ ( )‏ = 19.8 g U Molar AVOGADRO’S NUMBER 1 mol U 238.00g U
MOLE
(mol)‏
Mass
(g)‏
Molar
AVOGADRO’S
NUMBER
Particles
(atoms, fu or mc’s)‏ ( )‏ ( )‏
1 mol U
238.00g U
5.00 x atoms U
6.022 x 1023 atoms U
1 mol U
= 19.8 g U
How many grams of uranium are in 5.00 X 1022 atoms of pure uranium?

9. Find n = molar mass = 192.92g/mol
In order to determine the molecular formula of a compound you only need to know its empirical formula?
True
False
???
HF5
H2F10
Find n = molar mass = g/mol
empirical mass g/mol
n = 2

10. To find molecular formula…
A. Find empirical formula.
B. Find empirical mass
C. Find n = molar mass
empirical mass
D. Multiply all parts of
empirical formula by n

11. A compound having an approximate molar mass of g/mol has the following percent composition by mass. Determine its molecular formula.
42.87% C
3.598% H
28.55 % O
25.00% N
C2H2ON
C4H4O2N2
C6H6O3N3
CHON
none of the above

12. C6H6O3N3 n = molar mass empirical mass = 167g mol = 2.98 56.05 g/mol
Step 1) %  g
Step 2) g  mol
Step 3) mol
mol
Step 4) return
to whole
42.87% C
3.598% H
28.55% O
42.87g C
3.598g H
28.55g O
= 2 C X
= 3.57 mol C
/ 1.78 mol
= mol H
= 2 H
C2H2ON
= mol O
= 1 O
25.00% N
25.00g N
= mol N
/ 1.78 mol
= 1 N
n = molar mass
empirical mass
= g mol =
56.05 g/mol
C6H6O3N3

13. Determine the percent composition of sulfuric acid.
a) 28.57% H, % S, 57.14% O
b) 2.055% H, % S, 65.25% O
c) 1.02% H, % S, 16.31% O
d) none of the above

14. Determine the percent composition of sulfuric acid.
MOLAR MASS of H2SO4 = g/mol
% H = mass H = g . =
molar mass g
% S = mass S = g . =
molar mass g
% H = mass O = g . =
molar mass g
2.055% H, % S, 65.25% O

15. Percent Abundance Practice – Part I
Silicon has three naturally ocurring stable isotopes, silicon-28, silicon-29 and silicon-30 with respective percent abundances of 92.23%, 4.69% and 3.08%. What is the average atomic mass of silcon?
Weighted Average =
Value A (%A) + Value B (% B) + Value C (% C) + …
28amu (.9223) + 29amu (.0469) + 30 amu (.0308) =
28.11 amu