Elements, compounds and mixturesIB MYP Sciences: Flashcards

Exam questions on Elements, compounds and mixtures

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.
   Explain why a magnet cannot be used to remove the iron from sample 2.2 marks
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.
   Explain how simple distillation can be used to obtain pure water from seawater.2 marks
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.
   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