Types of mixtureIB MYP Chemistry: Subtopic test

1. 1
   A student looks up how much of two solids dissolves in 100 g of water to make a saturated solution. Potassium nitrate: 32 g at 20 °C, 64 g at 40 °C, 109 g at 60 °C and 169 g at 80 °C. Sodium chloride: 36 g at 20 °C, 36 g at 40 °C, 37 g at 60 °C and 38 g at 80 °C.

   (a)

   Which statement describes how the solubility of potassium nitrate changes with temperature?

   [1 mark]

   • AIt increases as the temperature rises
   • BIt decreases as the temperature rises
   • CIt stays the same at all temperatures
   • DIt increases and then decreases

   (b)

   A solution contains 109 g of potassium nitrate dissolved in 100 g of water at 60 °C. Which term describes this solution?

   [1 mark]

   • AAn unsaturated solution
   • BA saturated solution
   • CA suspension
   • DA colloid

   (c)

   Describe how the effect of temperature on the solubility of sodium chloride differs from its effect on potassium nitrate.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A food technologist classifies four products. Muddy river water has soil particles that can be seen and settle to the bottom after an hour. Sweet tea is clear, with the sugar particles too small to see. Mayonnaise has tiny droplets of oil spread through a water-based liquid and stays evenly mixed. A bronze coin is made by melting copper and tin together and letting the liquid solidify.

   (a)

   Which product is a suspension?

   [1 mark]

   • ASweet tea
   • BMayonnaise
   • CMuddy river water
   • DA bronze coin

   (b)

   Which product is an emulsion?

   [1 mark]

   • AMuddy river water
   • BSweet tea
   • CA bronze coin
   • DMayonnaise

   (c)

   Explain why bronze is classed as an alloy and as a mixture.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates how temperature affects how much potassium nitrate dissolves. She warms 20 g of water to each chosen temperature in a water bath, adds potassium nitrate in small portions while stirring, and records the total mass added when some solid will no longer dissolve. The total masses dissolved in 20 g of water were: 6.4 g at 20 °C, 12.8 g at 40 °C, 21.8 g at 60 °C and 33.8 g at 80 °C.

   (a)

   Describe the pattern in the results, using data from the investigation.

   [3 marks]

   (b)

   Evaluate the student's method and suggest improvements.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A company makes potassium nitrate for use as a crop fertiliser. It dissolves the solid in 200 g of water at 80 °C until the solution is saturated, filters it, then cools it to 20 °C so that crystals form. Potassium nitrate dissolves up to 169 g per 100 g of water at 80 °C and 32 g per 100 g of water at 20 °C. Farmers say the fertiliser increases their crop yields, but a nearby fishing community is worried about its effect on the river.

   (a)

   Calculate the mass of crystals formed when the solution is cooled, and explain why crystals form.

   [6 marks]

   (b)

   Discuss and evaluate the use of potassium nitrate as a fertiliser.

   [6 marks]

   Total for question 4: 12 marks

End of questions