Name:_____________________________________ Date:________________________________ Blk:____
Molehill
The molehill is a mnemonic for converting amongst moles, mass, volume of gas, concentration, and numbers of particles. In all cases a proper equation with units must be shown.
Draw the molehill.
1) What is the mass of 82.2 L of oxygen gas at STP?
2) What mass of colbalt (II) chloride must be dissolved to make 250.0 mL of 0.50 M solution?
3) How many chloride ions are dissolved in 750.0 mL of 1.20 M aluminum chloride solution?

Stoichiometry
Stoichiometry involves relating quantities of reactants and products through a balanced equation.
1) What volume of water vapour is formed when 50.0 g of ammonium dichromate decomposes to form chromium
(III) oxide, nitrogen, and water vapour.
2) Excess calcium phosphate in rock reacts with 2.0 M sulphuric acid. What is the concentration of the phosphoric acid formed?
3) When ammonia gas is passed over copper (II) oxide at high temperatures, nitrogen, copper, and water vapour are formed. If the ammonia gas is used up at a rate of 1.25 L per minute, at what rate is the copper forming in grams per second?
Dilutions
Many chemical reactions take place in solution therefore it is important to be able to make solutions of the appropriate concentration and calculate their new concentration upon dilution.
1a) How would you prepare 500.0 mL of 2.0 M copper (II) chloride solution?

b) What is the concentration of the chloride ions in the solution above? _______________ c) An experiment calls for 0.15 M copper (II) chloride solution. How would you prepare this solution from the 2.0
M stock solution you made previously?
2a) How would you prepare 50.0 mL of 4.0 M HCl from an 11.8 M stock solution?
b) If 10.0 mL of this solution was then removed and mixed with water to make 60.0 mL of solution, what is its new concentration?
3a) A solution of NaOH was prepare by dissolving 0.50 g in water to make 20.0 mL of solution. Next the NaOH solution was mixed with 20.0 mL of 0.80 M HCl solution. Calculate the concentration of the OH and H + ions right after the two solutions are mixed, but before any reaction occurs. b) Which ion is in excess? _____________ c) What concentration of the excess remains in solution?

Name:_____________________________________ Date:________________________________ Blk:____
Molehill
Caffeine has a molecular formula of C
8
H
10
O
2
N
4
. a) What is the mass of 1 molecule of caffeine? b) How many atoms of nitrogen are in 10.0 g of caffeine? c) A 250 mL cup of coffee has 120 mg of caffeine. What is the concentration of the caffeine in the coffee in mol/L?
Stoichiometry
Consider the reaction: 2MnO
4
(aq) + 6H + (aq) + 5H
2
C
2
O
4
(aq) ----> 2Mn 2+ (aq) + 8H
2
O(l) + 10CO
2
(g) a) What is the concentration of a sample of MnO
4
-
0.025 M H
2
C
2
O
4
?
if 17.82 mL is needed to completely react with 50.00 mL of b) What volume of CO
2
is produced at STP when 25.00 mL of 0.025M H
2
C
2
O
4
is reacted with excess MnO
4
?

d) In a separate reaction between H
2
C
2
O
4
and MnO
4
, it was found that the MnO
4
was used up at a rate of 0.080 mol/Lmin. If the total volume of the reaction mixture was 100.0 mL, at what rate was CO mL/min at STP?
2
being produced in
Dilutions a) How would you prepare 50.0 mL of 1.20 M NiCl
2
solution? b) What is the [Cl ] in this solution? ____________ c) How would you prepare 15.0 mL of 0.80 M NiCl
2
from the stock solution in “a”? d) After performing the dilution in ‘c’, the leftover 1.20 M stock solution of NiCl
AlCl
3
. What is the concentration of the individual ions in the final solution? What is the total ion concentration in the final solution?
2
is mixed with 25.0 mL of 0.75 M