Elements, compounds and mixturesIB MYP Sciences: Subtopic test

1. 1
   A chemistry teacher in Nairobi gives her class two samples. Sample 1 is a mixture made by stirring iron filings and yellow sulfur powder together. Sample 2 is iron(II) sulfide, a black solid made by heating iron and sulfur together strongly.

   (a)

   Which statement correctly describes the difference between the two samples?

   [1 mark]

   • AIn sample 2 the iron and sulfur are chemically combined, but in sample 1 they are not
   • BSample 1 contains iron but sample 2 contains no iron
   • CSample 2 is a mixture because it contains two elements
   • DSample 1 is a compound because it contains two elements

   (b)

   Which method would separate the iron from sample 1?

   [1 mark]

   • AFiltration
   • BSimple distillation
   • CUsing a magnet
   • DChromatography

   (c)

   Explain why a magnet cannot be used to remove the iron from sample 2.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A small salt works on the coast of Gujarat in India fills shallow pools with seawater. The Sun evaporates the water and salt crystals form. The workers also want to collect pure water from some of the seawater, and one sample of seawater they collected contains some sand.

   (a)

   In seawater, which term describes the dissolved salt?

   [1 mark]

   • ASolvent
   • BSolute
   • CFiltrate
   • DResidue

   (b)

   Which technique should the workers use to remove the sand from the sample of seawater?

   [1 mark]

   • ACrystallisation
   • BSimple distillation
   • CChromatography
   • DFiltration

   (c)

   Explain how simple distillation can be used to obtain pure water from seawater.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A food scientist uses paper chromatography to find out which dyes are in a blue-green sweet coating. She draws a pencil line near the bottom of a strip of chromatography paper and places a spot of the sweet's dye extract and spots of three known dyes (P, Q and R) on the line. She stands the paper in a beaker of water, with the water level below the line. She stops the experiment when the water has risen 9.0 cm above the pencil line.

   (a)

   The sweet extract produced two spots, at 3.6 cm and 6.3 cm above the pencil line. The known dyes have Rf values of 0.40 (P), 0.55 (Q) and 0.70 (R). Calculate the Rf value of each spot and state which known dyes are present in the sweet coating.

   [3 marks]

   (b)

   The scientist concludes that the coating contains only dyes P and R. Evaluate this conclusion and suggest two ways to improve the method.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Brazil produces large amounts of ethanol fuel by fermenting sugar from sugar cane. The fermented liquid is a mixture of ethanol and water. Ethanol boils at 78 °C and water boils at 100 °C. The ethanol is separated by fractional distillation and is blended with petrol or used on its own in cars.

   (a)

   Describe how fractional distillation is used to separate ethanol from the mixture of ethanol and water.

   [6 marks]

   (b)

   Evaluate the use of ethanol made from sugar cane as a fuel in Brazil. Discuss the benefits and drawbacks for people and the environment, and reach a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions