ACIDS• The common acids found in laboratory or in fruits/foods are as follows: Strong acid Weak acids Hydrochloric acid Citric acid Sulfuric acid Ethanoic acid Nitric acid Malic acid
PROPERTIES OFACIDS• All acids, either strong or weak, have the following properties:- Sour taste- Able to conduct electricity- Corrosive if concentrated- Able to turn blue litmus paper red- Able to react with metals, carbonate compounds and alkalis.
REACTION WITHMETALS• The reaction between metals and acids produce salts and hydrogen gas.• Acid + Metal Salt + Hydrogen• A lighted splint is used to test for the presence of hydrogen gas. It extinguishes the splint and gives a “pop” sound.
REACTION WITHCARBONATES• Acid react with carbonate compounds to produce salts, carbon dioxide and water.• Acid + Carbonate Salt + Carbon Dioxide + Water• Limewater is used to test for the presence of carbon dioxide gas. The limewater turns chalky when carbon dioxide is bubbled into it.
REACTION WITHALKALIS• Acid react with alkalis to produce salts and water only• The reaction between acids and alkalis is called the NEUTRALISATION reaction.• Acid + Alkalis Salt + Water• Universal indicator can be used to show that the solution has become neutral after the reaction. It gives a pale green color in neutral solutions.
USES OF ACIDSAcids UsesSulfuric acid Used in car batteriesHydrochloric acid Removes rust from iron and steelEthanoic acid Used in vinegars to preserve foodNitric acid Used in the production of fertilisers
PROPERTIES OFALKALIS• When dissolved in water, alkalis exhibit the following properties:- Soapy feeling- Turning red litmus paper blue- Able to conduct electricity- Corrosive if concentrated- Reaction with acids to form salt and water.• The common alkalis used in the school lab are sodium hydroxide, potassium hydroxide and ammonia.
USES OF ALKALISAlkalis UsesCalcium hydroxide They neutralize excess acid in soilAluminium hydroxide Used in antacid(or indigestion tablet)Magnesium hydroxide Used in antacid and toothpasteSodium hydroxide Used in making soaps and detergents
PH SCALE• The pH scale is a measure of the relative acidity or alkalinity of a solution.• Strong acid weak acid Weak alkali strong alkali
EXAMPLES• Examples of acidic and alkaline solutions in our daily lives:
INDICATOR• An indicator is a mixture of substances which shows different color in different pH values of solutions.• Universal indicator is an indicator which contains a mixture of substances that are able to give different colors corresponding to different pH values.• It can be used to determine the strength of acids and alkalis by observing the change of its color.• The table below shows the colors of Universal Indicator corresponding to the pH scale: pH scale 0-2 3-4 4-6 7 8-11 12-14 Color of Universal Red Orange Yellow Pale Green Violet Indicator green -blue
INDICATOR• Other types of indicator commonly used in the lab: Types of Acidic Neutral Alkaline indicator Litmus Red - Blue Phenolphtlein Colourless Colourless Pink ( > pH 9) Methyl Orange Red (< pH 3.5) Yellow Yellow