An acid is a substance that produces hydrogenions when dissolved in water. Examples of acids are hydrochloric acid (HCl),sulphuric acid (H2SO4), nitric acid (HNO3) andethanoic acid (CH3COOH). Sulphuric acid is used in detergents, fertilisers andcar batteries. Ethanoic acid is used in vinegar and makingadhesives. Hydrochloric acid is used in leather processing andcleaning materials.
Acids have a sour taste. Acids dissolve in water to form solutions thatconducts electricity. Acids turn blue litmus red. Acids have pH value less than 7. Acids react with metals, carbonates and bases.
Metal reactions Acid + Reactive Metal Salt + HydrogenCarbonate reactions Acid + Carbonate Salt + Water + Carbon dioxideBase reactions Acid + Base Salt + Water
Test for Hydrogen Place a lighted splint at the mouth of a test tube. A pop sound is heard and the splint is extinguished.Hydrogen is thus present. Test for Carbon dioxide Bubble the gas through limewater. If carbon dioxide is present, the limewater will turnchalky and a white precipitate would be formed.
An alkali is a metal oxide or hydroxide that issoluble in water. Examples : sodium hydroxide (NaOH) potassium hydroxide (KOH) calcium hydroxide [Ca(OH)2] barium hydroxide [Ba(OH)2] aqueous ammonia (NH3).
Ammonia solution Fertilisers Window cleaning solutions Calcium oxide To neutralise acidic soil Iron, concrete and cement Magnesium hydroxide Toothpaste to neutralise acid on teeth Antacids to relieve indigestion Sodium hydroxide Soaps and detergents Industrial-cleaning detergents
Alkalis have a bitter taste and soapy feel. Alkalis dissolve in water to produce hydroxideions. Alkalis turn red litmus blue. Alkalis have pH value more than 7. Alkalis react with metals, ammonium salts andacids
Metal reactions Alkali + Salt A Metal hydroxide + Salt BAmmonium salt reactions Alkali + Ammonium Ammonia + Water + SaltBase reactions Alkali + Acid Salt + Water
Taste Solubility Acids have a sour taste. Acids dissolve in waterto form solutions thatconducts electricity. Acids turn blue litmusred. Acids have pH value lessthan 7. Acids react with metals,carbonates and bases. Alkalis have a bittertaste and soapy feel. Alkalis dissolve in waterto produce hydroxideions. Alkalis turn red litmusblue. Alkalis have pH valuemore than 7. Alkalis react withmetals, ammonium saltsand acids.Litmus pH value Reactions
Test for Ammonia Place a piece of moist red litmus paper in thesolution If ammonia is present, the moist red litmus paperwill turn blue.
Indicator Colour in Acids pH value Colour in AlkalisMethyl orange Red 3 – 5 YellowScreened Methyl orange Violet 3 – 5 GreenLitmus paper Red 5 – 8 BlueBromothymol blue Yellow 6 – 8 BluePhenolphtalein Colourless 8 – 10 PinkRed cabbage juice Pink Nil GreenHydrangea flower Blue Nil Red
When an acid and alkali react together, theyneutralise each other. Their properties areremoved. The pH value of the acid is increased while the pHvalue of the alkali is decreased. The neutralmixture has a pH value of 7. Water is formed together with a new substancecalled a salt.
A salt is a ionic compound formed when a metallicor ammonium ion neutralises hydrogen ions of anacid. Calcium chloride CaO + 2 HCl CaCl2 + H2O Zinc sulphate ZnO + H2SO4 ZnSO4 + H2O Sodium nitrate NaOH + HNO3 NaNO3 + H2O