Elements, compounds and mixturesIB MYP Chemistry: Mind map

Exam questions on Elements, compounds and mixtures

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.
   Explain why container Z holds a mixture and not a compound.2 marks
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.
   Describe two differences between the mixture of iron and sulfur and the compound iron sulfide.2 marks
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.
   Calculate the percentage of the air that reacted with the copper, and state what this shows.3 marks