Compounds, Elements and Mixtures

Question 1

Define an atom and an element, giving examples.

4 marks

Answer 1

An atom is the smallest unit into which matter can be divided without the release of electrically charged particles, for example a hydrogen atom.
An element is a pure substance composed of only one type of atom, for example a gold nugget.

Question 2

Describe the structure of an atom and name the subatomic particles.

4 marks

Answer 2

An atom has a central nucleus orbited by electrons. The nucleus is made up of protons and neutrons and occupies a tiny space in the middle of the atom.
The subatomic particles are the proton, the neutron and the electron.

Question 3

Define a mixture and give examples.

2 marks

Answer 3

A mixture is when elements or compounds are mixed together without being chemically bonded. An example is seawater, a mixture of salt and water.

Question 4

Distinguish between a solute, a solvent and a solution.

3 marks

Answer 4

1. A solute is something being dissolved, usually a solid.
2. A solvent is something that is dissolving something else, usually a liquid.
3. A solution is a mixture of a solute and a solvent.

Question 5

1. What are the four methods for separationg mixtures?
2. Describe how to separate mixtures using these methods.

12 marks

Answer 5

Q1
* Filtration
* Evaporation
* Distillation
* Chromatography

Q2
* Pour the mixture through a funnel of filter paper. The larger solids will not be able to pass through the paper, but the liquid will.
* Evaporate the mixture to obtain only the solids.
* Boil the mixture. The liquid with the lower boiling point will evaporate first, leaving you with two separate mixtures.
* Put a spot of the mixture on some chromatography paper. Balance the paper in a shallow beaker of water. Depending on the solubility of the different components of the mixture, they will be separated out.

Question 6

Define a compound and give an example.

2 marks

Answer 6

A compound is two or more elements chemically bonded together. An example is iron oxide (rust).

Question 7

A ………. must occur for a compound to occur.

1 mark

Answer 7

Chemical reaction

Question 8

Define a chemical change and give examples of chemical changes.

2 marks

Answer 8

A chemical change is an irreversible reaction involving the formation of new substances. An example is wood burning.

Question 9

List some ways you can observe that a chemical reaction has taken place.

6 marks

Answer 9

• New substances formed
• Reactants used up
• Effervescence (bubbles)
• Heat/light/sound
• Electricity produced
• A precipitate (solid) formed

Question 10

How do you write a word equation? Define reactants and products.

3 marks

Answer 10

Reactants are the substances before a chemical reaction. Products are the substances after a chemical reaction.

A word equation is written like this:
REACTANTS ====> PRODUCTS

Question 11

How are compounds named?

4 marks

Answer 11

Compounds are named ………. ……….-ide, e.g. iron oxide (iron and oxygen). However, if oxygen is present, they are named -ate, e.g. copper sulfate (copper, sulfur and oxygen).
An exception is diatomic elements (elements that form compounds with other atoms of the same element), which are just called by their name, e.g. oxygen, which is a compound of two oxygen atoms.