Chemistry at Home Summary Notes

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1 Neutral Yellow Green Cyan Chemistry at Home Summary Notes Section 1 - Indicators Substances can be acid, alkali or neutral. Acid and alkali are the opposite of each other and neutral is in the middle. When we add an indicator to a substance the indicator changes colour. We can compare this colour to a chart to find out if the substance is acid, alkali or neutral. There are many different indicators. The one we use is called universal indicator or ph indicator. Section 2 ph Scale ph number Colour Red orange blue purple Type of solution Acid Alkai Section 3 ph of Household Substances. Substance Shampoo Detergent Cola Salt water Soap solution Indigestion remedy Disinfectant Hydrochloric acid Sulphuric acid Sodium hydroxide Vinegar Washing powder ph colour ph number Type of solution Acids have a ph less than 7. Neutralsolutions have a ph of 7. Alkali have a ph of more than 7. S2 Chemistry at Home Summary notes page 1

2 Two acids used in the lab are hydrochloric acid and sulphuric acid. Two acids used at home are cola and vinegar. An alkali used in the lab is sodium hydroxide. Two alkalis used at home are shampoo and detergent. The type of household substance which is usually alkaline is cleaning product. The type of household substance which is usually acidic is food. Section 4 - Neutralisation When an alkali is added to an acid the ph increases. When the ph reaches 7 we say that the acid has been neutralised. An indicator is used to follow the change in ph as the neutralistion reaction proceeds. Section 5 Everyday Neutralisation Indigestion is caused by too much acid in the stomach. Many indigestion remedies contain magnesium hydroxide, which will react with the acid and neutralise it. Wasp stings are alkaline so can be treated with vinegar which is an acid. The vinegar neutralises the alkali in the sting so the sting no longer hurts. Bee stings are acid so can be treated with baking soda (sodium hydrogencarbonate) which is an alkali. The baking soda neutralises the acid in the sting so the sting no longer hurts. Soil can become acid due for a variety of reasons eg acid rain, lots of organic matter in the soil. Many plants prefer an alkaline soil. Soil can be made more alkaline by adding lime to it. The lime (calcium oxide) neutralises the acid in the soil. S2 Chemistry at Home Summary notes page 2

3 Section 6 Reactions of Metals Metal Reaction with Air Reaction with Water Reaction with Acid Calcium - Quite fast - Copper No reaction No reaction No reaction Lithium Fast Fast - Magnesium Slow Very slow Fastest Sodium Very fast Very fast - Tin No reaction No reaction Slowest Zinc Slow No reaction Slow Section 7 Reactivity Series Most reactive Sodium Lithium Calcium Magnesium Zinc Tin Least Reactive Copper The more reactive the metal the more recently it was discovered. Some unreactive metals such as silver and gold were discovered in ancient times. Section 8 Uses of Metals and Alloys The metal is used to make. Advantages Disadvantages S2 Chemistry at Home Summary notes page 3

4 An alloy is a mixture of metals with other elements. Alloys have different properties to the elements they are made from. Alloy Elements it is Made From Uses Bronze Copper Tin Propellers Bells Swords Steel Duralumin Iron Carbon Aluminium Copper Magnesium Manganese Girders in buildings Cars Bridges Aircraft Section 9 - Simple Cells V Factors that affect the voltage of a simple cell are:- Type of electrolyte Volume of electrolyte Concentration of electrolyte Type of electrode Size of electrode Depth in solution Distance between electrodes For a simple cell to produce a voltage the two electrodes must be made from different metals. voltmeter wire metal electrode electrode made from a different metal electrolyte S2 Chemistry at Home Summary notes page 4

5 Section 10 Planning an Investigation and Writing a Report The following sections should be included in all investigation plans. Aim a simple sentence stating what you are trying to find out. Name of the variable you are changing. Name of the variable you are measuring. List of variables you will keep constant. Diagram that is drawn with a pencil and ruler and has labels Method a brief statement of what you are going to do. Results A results table with headings and units. The following sections should be included in all investigation reports. Results table with headings and units. It should have space for the first measurement, the second measurement and the average of the two measurements. Graph - Must be drawn on graph paper with a pencil and ruler. - Must take up more than half the graph paper. - Bar chart if one set of data iswords and a line graph if both sets of data are numbers. - Axes must be a number line with a simple scale based on 1, 2, 5, 10, 20 etc. - Both axes must have a label that includes the unit. - Points should be plotted accurately with an X. - Points should usually be joined with a straight line of best fit or a smooth curve of best fit. - A rogue point is a point that is a little way off the best fit line - The top and sides of bars must be drawn with a ruler. Conclusion A clear statement of the relationship between the variable changed and the variable measured. It must reflect the aim and be correct for the results. Evaluation A suggested improvement with a reason why this would make the results more accurate or reliable. S2 Chemistry at Home Summary notes page 5

6 Section 11 Electrochemical Series An electrochemical series is a list of metals starting with the one that gives the highest voltage when used to make an electricity in a simple chemical cell and going down to the metal that gives the lowest voltage when used as an electrode in a simple chemical cell. The voltage of a cell is the difference between the voltages of the metals used to make the electrodes. Electrons flow through the wires in a cell from the metal higher in the electrochemical series to the metal lower in the electrochemical series. Section 12 Hydrogen Fuel Cells Hydrogen fuel cells are a recent development in chemical cell technology. They use hydrogen and oxygen to make electricity. The hydrogen and oxygen can be made from water using solar energy which is a renewable source of energy. Fossil fuels are non renewable sources of energy that we burn to release energy. This damages the environment because burning fossil fuels releases carbon dioxide and other pollutant gases. Carbon dioxide adds to the greenhouse effect which is responsible for global warming. Hydrogen fuel cells only produce water which does not damage the environment. The main advantages and disadvantages of hydrogen fuel cells are: Advantages Disadvantages Do not pollute the environment. Hydrogen is a renewable energy source. Hydrogen contains less energy than fossil fuels. Hydrogen is explosive and difficult to store. The main use of hydrogen fuel cells is to power cars. S2 Chemistry at Home Summary notes page 6

Have a ph value less than ph 7 Turn blue litmus indicator red Can neutralise an alkali Have a sour taste (WARNING: never taste any chemicals)

Acids and Alkalis ACIDS (acidic solutions) Acids have the following properties: Have a ph value less than ph 7 Turn blue litmus indicator red Can neutralise an alkali Have a sour taste (WARNING: never