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