Elements, compounds and mixturesIB MYP Chemistry: Flashcards
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What is an element?
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- What is an element?
- A substance made of only one type of atom.
- What is a compound?
- A substance made of two or more different elements chemically bonded in a fixed ratio.
- What is a mixture?
- Two or more substances that are not chemically bonded, which can be separated by physical methods.
- Is O₂ an element or a compound?
- An element: it is a molecule made of two atoms of the same type.
- Is CO₂ an element, a compound or a mixture?
- A compound: its molecules contain carbon and oxygen atoms bonded together.
- How can you tell a compound from a mixture in a particle diagram?
- A compound has only one kind of particle, made of different atoms joined together; a mixture has two or more kinds of particle.
- How are the properties of a compound related to its elements?
- They are different from the properties of the elements it contains.
- How are the properties of a mixture related to its parts?
- Each part keeps its own properties.
- Can the proportions in a mixture vary?
- Yes. A compound has a fixed ratio but a mixture does not.
- How can a compound be split into its elements?
- Only by a chemical reaction, such as electrolysis.
- How can a mixture be separated?
- By physical methods such as filtering, evaporating, distilling or using a magnet.
- Is air an element, a compound or a mixture?
- A mixture of gases, mainly nitrogen and oxygen.
- What is a pure substance?
- A substance made of only one element or one compound.
Exam questions on Elements, compounds and mixtures
- 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
- 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
- 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
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).