2. Describe the definitions of element, mixture, molecule and compounds An element is a pure substance that cannot split up into two or more simpler substances by chemical processes or by electricity. A mixture is a group of two or more elements and/or compounds that are not chemically combined. Alloys are mixtures of metals with other elements, usually another metal. A molecule is a group of two or more atoms that are chemically combined together. A compound is a pure substance that contains two or more elements chemically combined.
3. Give examples of mixtures Sea water (Water and Salt) Air (Nitrogen, Oxygen, Water Dioxide, Carbon Dioxide, etc.) Bronze (Copper and Tin) Brass (Zinc and Copper) Stainless Steel (Iron, Chromium, Nickel and Carbon) Steel (Iron and Carbon)
4. Describe common properties of mixtures Separation – It can be separated into its components by physical methods Properties – The chemical properties of the mixture are the same as those of its components. Energy – No energy change takes place when formed, i.e. no heat or light is taken in or given out. Composition – The substances in a mixture can be mixed in any proportion.
5. Distinguish among compounds and mixtures A mixture can be separated by physical methods while a compound can only be separated by chemical reactions or electricity. A mixture has the same properties as its components while a compound’s physical and chemical properties are different from the elements of the compound. No chemical reaction takes place when a mixture is formed while a chemical reaction takes place when a compound is formed. The components of a mixture can be mixed in any proportion while the elements of a compound are always combined in fixed proportion by mass.
6. Distinguish among solute, solvent and solution A solute is the substance that dissolves in a liquid. A solvent is the liquid that dissolves other substances. A solution is a liquid that forms when a solute dissolves in a solvent.
7. Determine the nature and properties of solutions Clear – A solution is clear and able to be seen through. Homogenous – A solution is homogenous, i.e. every part of the solution has the same properties. Composition – The solute particles will not settle to the bottom. Size – Solute particles in the solution can pass through filter paper.
8. Investigate the factors that affect the solubility and rate of dissolving Solubility is the amount of solute that can dissolve in a given amount of solvent. A saturated solution is a fully dissolved solution where no more solute dissolves. The factors affecting solubility are the type of solute, type of solvent and temperature.
9. Give examples of the importance of these factors When sugar is added to tea, the hot water and stirring dissolve sugar more quickly. In a washing machine, soap and dirt dissolve fast as washing is done at a high temperature, soap is in the form of powder and the contents are agitated. Fertilisers contain minerals that dissolve in water in soil easily. Many soft drinks contain dissolved sugar because of its high solubility in water.
