Pupil sheet · The mole

How much solute is in the solution? — questions

Name ______________________ Date ____________

Try every question before you use a nudge. Write in full sentences where you are asked to explain.

1. state

In which units can the concentration of a solution be measured? Choose all that apply.

Tick every correct statement.

g/mol
dm³
g/dm³
mol/dm³

Nudge (only if you are stuck): For each unit, ask: is a quantity of solute divided by a volume of solution?

2. calculate

Supplement. 0.0144 mol of a solute is made into 80.0 cm³ of solution. (a) Calculate the volume in dm³. (b) Calculate the concentration in mol/dm³. Give each calculated answer to three significant figures.

(a) Volume: ______________ unit ________

(b) Concentration: ______________ unit ________

Nudge (only if you are stuck): Concentration is per dm³. Which unit must the volume be in before you divide?

3. calculate

Supplement. 7.80 g of magnesium sulfate, MgSO₄, is made into 500.0 cm³ of solution. (Ar: O 16, Mg 24, S 32.) Calculate (a) the concentration in g/dm³, (b) the amount of magnesium sulfate, (c) the concentration in mol/dm³. Give each calculated answer to three significant figures.

(a) Concentration in g/dm³: ______________ unit ________

(b) Amount: ______________ unit ________

Nudge (only if you are stuck): Both concentrations use the same volume. Which unit must it be in?

4. calculate / deduce / identify

Supplement. A technician dissolves 3.12 g of a white solid and makes it up to 200.0 cm³ of solution. Its concentration is 0.110 mol/dm³. (a) Calculate the amount of solid dissolved. (b) Calculate the molar mass of the solid. (c) Deduce its relative formula mass, to the nearest whole number. (d) The solid is one of NaCl, KNO₃, Na₂CO₃ or Na₂SO₄. Identify it. Give each calculated answer to three significant figures. (Ar: C 12, N 14, O 16, Na 23, S 32, Cl 35.5, K 39.)

(a) Amount: ______________ unit ________

(b) Molar mass: ______________ unit ________

(d) The solid

Nudge (only if you are stuck): Two steps: the amount in the flask first, then the grams in each mole.

5. calculate / determine

Supplement. (a) A solution of sulfuric acid, H₂SO₄, has a concentration of 4.90 g/dm³. Calculate its concentration in mol/dm³. (Ar: H 1, O 16, S 32.) (b) A solution of a metal hydroxide has a concentration of 8.96 g/dm³, which is 0.160 mol/dm³. Determine the molar mass of the hydroxide. Give each calculated answer to three significant figures.

(a) Concentration in mol/dm³: ______________ unit ________

(b) Molar mass: ______________ unit ________

Nudge (only if you are stuck): Think about one dm³: how many grams and how many moles are in it?

6. deduce

Supplement. A pupil makes 200.0 cm³ of copper(II) chloride solution in a volumetric flask. The flask is still wet inside with distilled water from washing it. She weighs the right mass of solid, dissolves it, rinses it all into the flask and makes it up to the line correctly. Which row is correct?

Row	Volume of solution	Amount of solute	Concentration compared with the plan
A	more than 200.0 cm³	as planned	lower
B	200.0 cm³	as planned	lower
C	200.0 cm³	as planned	the same
D	less than 200.0 cm³	as planned	higher

Circle one answer.

Nudge (only if you are stuck): Follow the water that was already in the flask: where does it end up?

7. deduce

Supplement. A pupil makes 100.0 cm³ of a solution in a volumetric flask. She stops adding water when the edges of the meniscus, where the water touches the glass, reach the line. Which row is correct?

Row	Volume of solution	Amount of solute	Concentration compared with the plan
A	less than 100.0 cm³	as planned	higher
B	more than 100.0 cm³	as planned	lower
C	less than 100.0 cm³	less than planned	the same
D	100.0 cm³	as planned	the same

Circle one answer.

Nudge (only if you are stuck): Where is the bottom of the curved surface when its edges touch the line?

8. calculate

Supplement. (a) Calculate the amount of solute in 40.0 cm³ of 0.350 mol/dm³ solution. (b) A second solution has a concentration of 6.40 g/dm³. Calculate the volume of it, in dm³, that contains 0.960 g of solute. Give each calculated answer to three significant figures.

(a) Amount: ______________ unit ________

(b) Volume: ______________ unit ________

Nudge (only if you are stuck): In (a), which unit must the volume be in? In (b), which unit does g ÷ g/dm³ leave?

9. calculate

Supplement. A pupil needs 0.00450 mol of a solute from a 0.300 mol/dm³ solution. Calculate the volume of solution she needs (a) in dm³ and (b) in cm³. Give each calculated answer to three significant figures.

(a) Volume in dm³: ______________ unit ________

(b) Volume in cm³: ______________ unit ________

Nudge (only if you are stuck): Rearrange c = n/V so the volume is on its own.

10. calculate

Supplement. A technician needs 500.0 cm³ of sodium carbonate solution that holds 3.18 g/dm³ of Na₂CO₃. She has only washing-soda crystals, Na₂CO₃·10H₂O. (Ar: H 1, C 12, O 16, Na 23.) Calculate (a) the mass of Na₂CO₃ the solution must hold, (b) the amount of Na₂CO₃, (c) the mass of washing-soda crystals she must weigh out. Give each calculated answer to three significant figures.

(a) Mass of Na₂CO₃: ______________ unit ________

(b) Amount of Na₂CO₃: ______________ unit ________

Nudge (only if you are stuck): Each crystal formula unit has one Na₂CO₃ in it. What does that tell you about the two amounts?

11. calculate

Supplement. A syringe delivers 5.00 cm³ of 0.0800 mol/dm³ calcium chloride solution, CaCl₂, into a test tube. (Ar: Cl 35.5, Ca 40.) Calculate (a) the amount of calcium chloride in the test tube, (b) the total number of ions in it, (c) the concentration of the solution in g/dm³. Give each calculated answer to three significant figures. (Avogadro constant: 6.02 × 10²³ per mol.) You can type 1.23 × 10⁻⁴ as 1.23x10⁻⁴.

(a) Amount of calcium chloride: ______________ unit ________

(b) Ions: ______________ unit ________

Nudge (only if you are stuck): Volume in dm³ first. How many ions does each CaCl₂ give?