Which of the following correctly defines concentration in mol L⁻¹?
A
The mass of solute per litre of solvent
B
The number of moles of solute per litre of solution
C
The number of moles of solvent per litre of solute
D
The volume of solute divided by the volume of solution
Question 2 — L06 Concentration calculation
0.400 mol of KNO₃ is dissolved in water and made up to 250 mL. What is the concentration of the solution?
A
0.100 mol L⁻¹
B
0.800 mol L⁻¹
C
1.60 mol L⁻¹
D
4.00 mol L⁻¹
Question 3 — L07 Primary Standards
Which property of a primary standard reduces the percentage error introduced by the analytical balance?
A
High purity
B
Stability in air
C
Solubility in water
D
High molar mass
Question 4 — L07 Dilution
50.0 mL of 4.00 mol L⁻¹ HCl is diluted to 400 mL. What is the final concentration?
A
0.500 mol L⁻¹
B
2.00 mol L⁻¹
C
0.250 mol L⁻¹
D
32.0 mol L⁻¹
Question 5 — L08 Percentage Purity
A 10.0 g sample of NaOH is 92.0% pure. What mass of pure NaOH is present?
A
0.800 g
B
9.20 g
C
10.9 g
D
8.00 g
Question 6 — L09 Gravimetric Analysis
In gravimetric analysis, why must the precipitate be insoluble in the solution?
A
So it can be easily identified by colour
B
So it dries quickly in the oven
C
So all the analyte is converted to precipitate and none remains dissolved
D
So the precipitate does not react with the filter paper
Question 7 — L09 Gravimetric Calculation
A gravimetric experiment produces 0.2334 g of BaSO₄. Using MM(BaSO₄) = 233.4 g mol⁻¹ and the equation Ba²⁺ + SO₄²⁻ → BaSO₄, what are the moles of SO₄²⁻?
A
0.2334 mol
B
2.00 × 10⁻² mol
C
2.00 × 10⁻³ mol
D
1.00 × 10⁻³ mol
Question 8 — L10 Titration Procedure
A student records the following titres: rough = 21.50 mL, then 20.35 mL, 20.30 mL, 21.10 mL. Which titres are concordant, and what is the correct average to use?
A
All three accurate titres; average = 20.58 mL
B
20.35 and 20.30 mL; average = 20.33 mL
C
All four including rough; average = 20.81 mL
D
20.30 and 21.10 mL; average = 20.70 mL
Question 9 — L10 Titration Calculation (1:1)
25.00 mL of NaOH is titrated against 0.1200 mol L⁻¹ HCl. The average titre is 22.50 mL. What is c(NaOH)? [HCl + NaOH → NaCl + H₂O]
A
0.1080 mol L⁻¹
B
0.1333 mol L⁻¹
C
0.1080 mol L⁻¹
D
0.2160 mol L⁻¹
Question 10 — L10 Mole Ratio
In the reaction H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O, 0.0300 mol of NaOH reacts completely. How many moles of H₂SO₄ reacted?
A
0.0150 mol
B
0.0300 mol
C
0.0600 mol
D
0.0900 mol
Section B — Short Answer
5 questions · 4 marks each · 20 marks
Question 11 — L06/L08 · Concentration + Purity4 MARKS
A student has a sample of potassium hydroxide (KOH) that is 94.0% pure. They dissolve 8.00 g of the impure sample in water and make up to 500.0 mL of solution.
(a) Calculate the mass of pure KOH in the sample. (1 mark) (b) Calculate the moles of KOH present. (1 mark) (c) Calculate the concentration of the KOH solution. (2 marks) (K = 39.098, O = 15.999, H = 1.008)
Question 12 — L07 · Standard Solutions + Dilution4 MARKS
A student prepares a 250.0 mL standard solution of sodium carbonate (Na₂CO₃) by dissolving 1.325 g of anhydrous Na₂CO₃ in distilled water.
(a) Calculate the concentration of the standard solution. (2 marks) (b) 40.0 mL of this standard solution is then diluted to 200 mL. Calculate the concentration of the diluted solution. (2 marks) (Na = 22.990, C = 12.011, O = 15.999)
A 200 mL sample of spa pool water is analysed for its chloride content using gravimetric analysis with AgNO₃. The filter paper has a mass of 1.0842 g. After filtration and drying, the filter paper plus AgCl precipitate has a mass of 1.6628 g.
(a) Calculate the mass of AgCl collected. (1 mark) (b) Calculate the moles of Cl⁻ in the sample. (1 mark) (c) Calculate the concentration of Cl⁻ in mol L⁻¹. (1 mark) (d) Express the Cl⁻ concentration in g L⁻¹. (1 mark) (Ag = 107.87, Cl = 35.453)
A student titrates 25.00 mL of H₂SO₄ solution against 0.1500 mol L⁻¹ NaOH. The titration data is as follows:
Rough titre: 28.60 mL Titre 1: 27.85 mL Titre 2: 27.90 mL Titre 3: 28.45 mL
Equation: H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
(a) Identify the concordant titres and calculate the average. (1 mark) (b) Calculate the moles of NaOH used. (1 mark) (c) Calculate the moles of H₂SO₄. (1 mark) (d) Calculate the concentration of H₂SO₄. (1 mark)
An impure sample of Na₂CO₃ (mass = 1.500 g) is dissolved in water and made up to 250.0 mL. A 25.00 mL aliquot is titrated against 0.2000 mol L⁻¹ HCl. The average concordant titre is 21.60 mL.
Equation: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂
(a) Calculate the moles of HCl used. (1 mark) (b) Calculate the moles of Na₂CO₃ in the aliquot. (1 mark) (c) Calculate the total mass of Na₂CO₃ in the 250 mL solution. (1 mark) (d) Calculate the percentage purity of the Na₂CO₃ sample. (1 mark) (MM of Na₂CO₃ = 105.99 g mol⁻¹)
Note: A result >100% indicates an error in the question data. In an exam, present the calculation and note the anomaly — full marks are awarded for correct method.