Chemistry 11 (HL)
Unit 3 / IB Topic 1.5
Quantitative Chemistry 4
Solutions and Concentrations - ANSWERS
PRACTICE PROBLEMS
1.
2.
Convert these units:
3
a)
0.035 L = 0.035 dm = 35 mL = 35 cm
b)
57.9 cm = 0.0579 dm
3
3
3
4.5 g of potassium nitrate is dissolved in 80.0 mL of water. Calculate the molar
concentration of the solution.
1. Find moles of KNO3:
mol KNO3 = 4.5 g x
1 mol
= 0.045 mol
101.11 g
n
V
0.045 mol
=
0.0800 L
= 0.56 mol L−1
C=
2. Find the concentration:
3.
Vinegar is a dilute solution of acetic acid (HC2H3O2). What mass of acetic acid is
-3
present in a 2.0 L jug of vinegar with a concentration of 0.658 mol•dm ?
n=CxV
1. Find the moles of acetic acid:
2. Find the mass of acetic acid:
4.
= 0.659 mol dm−3 x 2.0 dm3
= 1.3 mol
mass = 1.3 mol x
60.60 g
= 79 g
1 mol
You are given a 0.35 M solution of silver nitrate (AgNO3). Calculate:
a)
the volume that contains 0.20 mol of silver nitrate.
n
V
0.20 mol
0.35 M =
V
V = 0.57 L
C=
p. 1
Chemistry 11 (HL)
b)
Unit 3 / IB Topic 1.5
the volume that contains 2.00 g of silver nitrate.
1. Find the moles of AgNO3:
1 mol
= 0.0118 mol
169.88 g
mol AgNO3 = 2.00 g x
n
V
0.0118 mol
0.35 M =
V
V = 0.034 L
C=
2. Find the volume:
5.
3
What mass of copper (II) sulfate pentahydrate crystals is present in 17.3 cm of a
-3
0.279 mol dm solution of copper sulfate?
n=CxV
= 0.279 mol dm−3 x 0.0173 dm3
= 0.00483 mol
1. Find moles of CuSO4:
mass = 0.00483 mol x
2. Find mass of CuSO4•5H2O
6.
249.71 g
= 1.21 g
1 mol
-3
You want to perform an experiment that needs a 3.5 x 10 M solution of potassium
bromide. You only have 57.0 g of potassium bromide. What volume of the solution
can you make?
mol KBr = 57.0 g x
1. Find the moles of KBr:
1 mol
= 0.479 mol
119.01 g
n
V
0.479 mol
M=
V
V = 137 L
C=
3.5 x 10−3
2. Find the volume:
7.
3
-3
How would you prepare 500 cm of a 0.25 mol dm solution of iron (III) nitrate?
n=CxV
1. Find moles of Fe(NO3)3:
2. Find mass of Fe(NO3)3:
= 0.25 mol dm−3 x 0.500 dm3
= 0.125 mol
mass = 0.125 mol x
106.97 g
= 13.4 g
1 mol
p. 2
Chemistry 11 (HL)
Unit 3 / IB Topic 1.5
3
To prepare the solution, add 13.4 g of Fe(NO3)3 to a 500.0 cm volumetric flask and
add water up to the mark. Swirl to dissolve.
8.
If you add 50 mL of water to 120 mL of a 0.45 M solution of NaCl, what is the new
concentration of the diluted NaCl solution?
C1V1 = C2 V2
(0.45 M) (120 mL) = C2 (120 + 50 mL)
C2 = 0.32 M
9.
You have 200 mL of a 2.0 M HCl solution. What volume of water must you add to
this solution in order to dilute the solution to 0.75 M?
1. Find the new TOTAL volume of the diluted solution:
C1V1 = C2 V2
(2.0 M) (200 mL) = (0.75 M) V2
V2 = 533 mL
2. Find the volume of water required to dilute to the new total volume:
V2 = V1 + VH O
2
533 mL = 200 mL + VH O
2
VH O = 333 mL
2
p. 3