Honors Chemistry I
Mole Concept Problem Set #3
Solution Set
1. What is the number of chlorine atoms in 34.7 grams of perchloric acid?
34.7 g. cpd. ( 1 mol cpd. / 100.5 g. cpd.)( 1 mol Cl / 1 mol cpd.)(6.02 x 1023 Cl atoms / 1 mol Cl)
= 2.08 x 1023 atoms of Cl
2. If you had 3.00 moles of auric nitrate, how many grams of pure gold could you get from this sample?
3.00 mol cpd. ( 1 mol Au / 1 mol cpd.) ( 197.0 g Au / 1 mol Au) = 591 g Au
3. How many total atoms are in exactly 1.000 microgram of pure, distilled water?
1.000 x 10-6 g cpd.( 1 mol cpd. / 18.0 g. cpd.)(3 mol atoms / 1 mol cpd.)(6.02 x 1023 atoms / 1 mol cpd)
= 1.00 x 1017 atoms total
4. How many grams of sodium chloride would you need in order to have the same number of sodium ions as
you have in 43.9 grams of sodium peroxide?
43.9 g Na2O2
1 mol Na2O2
2 mol Na
1 mol NaCl
58.5 g NaCl
x --------------- x -------------- x -------------- x --------------- = 65.9 g NaCl
78.0 g Na2O2 1 mol Na2O2
1 mol Na
1 mol NaCl
5. How many moles of hydrochloric acid do you need in order to release 10.0 liters of hydrogen gas at STP?
10.0 L (1 mol H2 / 22.4 L H2) ( 2 mol HCl / 1 mol H2) = 0.893 mol H2
6. How many liters of gas do you have if you have 80.0 grams of carbon dioxide? (Assume STP)
80.0 g CO2 (1 mol CO2 / 44.0 g CO2) (22.4 L CO2 / 1 mol CO2) = 40.7 L
7. If you had the same volume of gas at the same STP, but the gas is changed to helium gas, how many more
moles of gas would you have?
no more moles; 22.4 L per mole is a constant @STP for any gas
23
8. A certain compound is composed of 1.505 x 10 atoms of potassium, 13.0 grams of chromium, and 0.875
moles of oxygen. What is the simplest whole number mole ratio of elements in this compound?
23
K 1.505 x 10 atoms / 6.02 x 1023 = 0.250 mol K
Cr 13.0 g / 52.0 g/mol = 0.250 mol Cr
& 0.875 mol O
K : Cr : O => 0.250 : 0.250 : 0.875 (divide all by 0.250) = 1: 1: 3.5 =>
K2Cr2O7
2:2:7
or potassium dichromate
9. If a compound of chromium chloride contains 32.8% chromium by weight, how many chloride ions are
there in 30.0 grams of this compound?
30.0 g cpd
67.2 g Cl
1 mol Cl
6.02 x 1023 Cl atoms
x --------------- x -------------- x --------------------------100 g cpd
35.5 g Cl
1 mol Cl
= 3.42 x 1023 Cl atoms
10. How many ions (total of both cations and anions) are there in 80.5 grams of barium phosphate?
80.5 g cpd
1 mol cpd
5 mols ions
6.02 x 1023 ions
x --------------- x -------------- x --------------------------601.9 g cpd
1 mol cpd
1 mols ions
= 4.03 x 1023 ions