Elements, compounds and mixturesIB MYP Chemistry: Subtopic test

1. 1
   A student examines four sealed containers using a particle model. Container W holds identical separate atoms of one type. Container X holds identical molecules, each made of two atoms of the same type joined together. Container Y holds identical molecules, each made of one carbon atom joined to two oxygen atoms. Container Z holds two different kinds of molecule that are simply mixed together, in a proportion that can vary.

   (a)

   Which containers hold an element?

   [1 mark]

   • AW only
   • BX only
   • CW and X
   • DW, X and Y

   (b)

   Which container holds a compound?

   [1 mark]

   • AContainer W
   • BContainer X
   • CContainer Z
   • DContainer Y

   (c)

   Explain why container Z holds a mixture and not a compound.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A teacher stirs iron filings and sulfur powder together to make a yellow-grey powder. A magnet pulls the iron filings out of the powder, leaving the yellow sulfur behind. She then heats a fresh sample of the powder strongly. It glows, and a dark grey solid called iron sulfide forms. The iron sulfide is not attracted to a magnet, and it contains iron and sulfur in a fixed ratio.

   (a)

   Which statement is correct about the powder before heating?

   [1 mark]

   • AThe iron and sulfur are chemically bonded
   • BEach substance keeps its own properties
   • CIt has a fixed composition
   • DIt can only be separated by a chemical reaction

   (b)

   Which observation shows that a new substance was formed when the powder was heated?

   [1 mark]

   • AThe product is not attracted to a magnet
   • BThe powder was a solid at the start
   • CThe powder contained two different substances
   • DThe sulfur was yellow

   (c)

   Describe two differences between the mixture of iron and sulfur and the compound iron sulfide.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student hypothesises that air is a mixture and not a compound. She traps 100 cm³ of dry air in a gas syringe and passes it slowly back and forth over heated copper. The copper turns black. When the apparatus has cooled, the syringe reads 79 cm³. A lit splint placed in the remaining gas goes out.

   (a)

   Calculate the percentage of the air that reacted with the copper, and state what this shows.

   [3 marks]

   (b)

   Evaluate the student's hypothesis that air is a mixture, using the evidence and suggesting one improvement.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A town treats its drinking water with chlorine. Some residents complain about the taste and ask the council to stop. The council points out that chlorine is an element that exists as a toxic green gas, and that sodium is a soft metal that reacts violently with water, yet sodium chloride, formed from the two, is the safe table salt found in every kitchen.

   (a)

   Explain why sodium chloride is safe to eat even though sodium and chlorine are both dangerous.

   [6 marks]

   (b)

   Discuss and evaluate whether the council should keep using chlorine to treat the water.

   [6 marks]

   Total for question 4: 12 marks

End of questions