Answers Mixtures
Year 7 Science Chapter 4
p75 1 A pure substance has a definite and consistent composition. Pure water is a pure substance consisting
only of water atoms (H2O).
2 Pure salt is a pure substance because it consists only of salt atoms (NaCl).
Pure gold is a pure substance because it consists only of gold atoms (Au).
3 A mixture is a mix of two or more substances.
• The substances can be solid, liquid, or gas.
• The substances can be mixed together in any proportion.
• When the substances are mixed there is no chemical reaction to make new substances.
• A mixture can be separated into its substances.
4 Salt water is a mixture because it is a mix of two or more substance (salt and water).
Smog is a mixture because it is a mix of a number of substances suspended in air .
5 Smog may be separated from air by using filters (eg face masks). Smog may also be separated from
air by bubbling the poluted air through water.
p77 1 a) The solute is coffee.
b) the solvent is hot water.
2 A solution of sugar and water is an example of a homogeneous mixture. A homogeneous mixtures is
well mixed. The particles that make up a homogeneous mixture are very small and do not settle out
when allowed to stand.
3 A mixture of sand and water is an example of a heterogeneous mixture. Heterogeneous mixtures are
the least mixed. The particles of a heterogeneous mixture are large enough to be seen. The particles
will settle out on standing.
4 A solution is a homogeneous mixture.
5 When a solution is passed through a filter no residue (solute) is left behind.
6 If a solution is left to stand, no solid particles (solute) settle to the bottom.
7 A stirred mixture of coffee and hot water is a solution. The coffee will not settle to the bottom if left to
stand. If the coffee and water is passed through a filter no residue is left behind.
8 Other solutes such as sugar are often added to a cup of coffee.
p79 1 A suspension is a heterogeneous mixture from which particles will eventually settle.
2 A suspension has solid particles that be left on filter paper.
3 A suspension has solid particles that will settle.
4 A colloid is between a solution and a suspension. A colloid is a heterogeneous mixture. A colloid has
particles larger than that of a solution but smaller than that of a suspension.
5 A colloid is between a solution and a suspension. A colloid is a heterogeneous mixture. A colloid has
particles larger than that of a solution but smaller than that of a suspension.
6 A colloid will show the beam of light.
7 Water in flood - suspension, water in a swimming pool - solution, sea water - colloid, milk - colloid,
orange juice - suspension, jelly - solution, beer - colloid.
