Concentration and gas volumesIB MYP Chemistry: Subtopic test

1. 1
   A pharmacist in Lagos prepares a saline solution for a clinic by dissolving 4.5 g of sodium chloride in water and making the solution up to 500 cm³.

   (a)

   What is the concentration of the solution in g dm⁻³?

   [1 mark]

   • A2.25 g dm⁻³
   • B4.5 g dm⁻³
   • C9.0 g dm⁻³
   • D0.009 g dm⁻³

   (b)

   The relative formula mass of sodium chloride is 58.5. What is the concentration of the solution in mol dm⁻³, to two significant figures?

   [1 mark]

   • A0.15 mol dm⁻³
   • B0.077 mol dm⁻³
   • C0.31 mol dm⁻³
   • D13 mol dm⁻³

   (c)

   The pharmacist needs 250 cm³ of this solution for a patient. Calculate the mass of sodium chloride in 250 cm³ of the solution.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student in Singapore reacts magnesium ribbon with excess dilute hydrochloric acid at room temperature and pressure. The equation is Mg + 2HCl → MgCl₂ + H₂. At room temperature and pressure, one mole of any gas occupies 24 dm³. The relative atomic mass of magnesium is 24.

   (a)

   The student uses 0.60 g of magnesium. How many moles of magnesium is this?

   [1 mark]

   • A14 mol
   • B40 mol
   • C0.25 mol
   • D0.025 mol

   (b)

   In a second experiment a smaller piece of magnesium gives 120 cm³ of hydrogen gas. How many moles of hydrogen is this?

   [1 mark]

   • A5.0 mol
   • B0.0050 mol
   • C0.050 mol
   • D2.9 mol

   (c)

   Calculate the volume of hydrogen, in cm³, produced when all of the 0.60 g of magnesium reacts.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A quality-control chemist at a food factory in Seville checks the concentration of a sodium hydroxide cleaning solution by titration. She measures 25.0 cm³ of the cleaning solution into a conical flask and adds hydrochloric acid of concentration 0.100 mol dm⁻³ from a burette until the indicator changes colour. The mean titre is 20.0 cm³. The equation is NaOH + HCl → NaCl + H₂O.

   (a)

   Calculate the number of moles of hydrochloric acid used in the titration.

   [3 marks]

   (b)

   Calculate the concentration of the sodium hydroxide solution in mol dm⁻³ and in g dm⁻³. The relative formula mass of sodium hydroxide is 40.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A cement company near Dubai heats limestone (calcium carbonate) strongly to make lime, a process that releases carbon dioxide. In the company's laboratory a technician checks the purity of limestone samples by reacting them with excess dilute hydrochloric acid and measuring the volume of carbon dioxide produced at room temperature and pressure.

   (a)

   A 0.50 g sample of limestone is reacted with excess acid and gives 108 cm³ of carbon dioxide. The equation is CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. Assume the sample is pure calcium carbonate (relative formula mass 100). Calculate the volume of carbon dioxide expected and the percentage of this volume that was collected. Suggest one reason why the volume collected is lower than expected and one change to the method that would improve it.

   [6 marks]

   (b)

   Lime and cement are essential for building homes and roads, but making them releases a lot of carbon dioxide. Discuss the benefits and drawbacks of the company making lime from limestone, and evaluate whether the company's production should continue.

   [6 marks]

   Total for question 4: 12 marks

End of questions