Acid and AlkaliChapter 5.5Nasrul IrfanMuhammad UmarMohd YasirDiaeden
Acid And Alkali• Acid and alkali are very usefull substances in ourdaily lives.What are the properties of acid andalkali? How do we neutralise acid and alkali?• The properties of acid and alkaliThe word acid comesFrom the latin word‘acidus’,which meansSour.Acid is present inFruits and many itemsWe use daily.
• Acid is a substance with a sour taste,turnsblue litmus red, is corrosive and reactswith metals to give hydrogen gas. It has apH value less than 7.• Alkali is a substance with a bitter taste andsoapy feel, turns red litmus blue and iscorrosive.It has a pH value greater than 7.
Properties of acid and alkaliProperties of acid Properties of alkali•Has a pH value less than 7 •Has a pH value greater than 7•Has a sour taste •Has a bitter taste and feels soapy•Corrosive •Corrosive•Turns blue litmus red •Turns red litmus blue•Reacts with most metals
The role of water in showing theproperties of acid and alkali.When a piece of dry blue litmus paper is added to solidcitric acid, there is no change in colour. But when weadd water to it, the litmus paper turns red.This showsthat acid only shows its properties in the presence ofwater.Similarly, when a piece of red litmus paper is added tosolid barium hydroxide,no clours change occurs.Butwhen we add water to it, the litmus paper turns blue.
Uses of alkalisSodium Hydroxide → Used for making soap and detergentAmmonia → Used as household cleaner,to makefertiliserMagnesium hydroxide → Used in antacid to ease stomachachedue to excess acidCalcium hydroxide → Used to raise the pH value of acidic(lime) soil for healthy growth of plants
Uses of acidsNitric acid → To make fertiliser and dyeCitric acid and tartaric acid → To make fruit saltAcetic acid → To make syntetic fibreBoric acid → Used as an eyewashBenzoic acid → Used to preserve foodAsorbic acid → Used to prevent scurvyCarbonic acid → Used to prepare carbonated drinks
NeutralisationWhen an acid reacts with an alkali, a solution containing a salt isformed. This process is called neutralisation.The general wordequation for the neutralisation process is:Acid+ alkali → salt+ waterReactions of various kinds of acids and alkalis will producedifferent types of salt. Here are some examples:Hydrochloric acid + sodium hydroxide → sodiumchloride + water sulphuric acid + potassiumhydroxide → potassium sulphate + water nitric acid +calcium hydroxide → calcium nitrate + water
Application of neutralisationNeutralisation is an important process. It produces various types of salts whichare very usefull.Salts are used extensively in flavouring food, treating icyroads and making fertiliser,gunpowder, glass and paint.The neutralisation process itself is useful in our daily life.Here are someexamples of the application of neutralisation:• Hair is healthy and strong when it is slightly acidic, but shampoos are usuallyslightly alkaline. Therefore, washing hair with alkaline shampoo makes hairlook dull and coarse.Hair conditioner which is acidic can be used toneutralise the residue of shampoo on the hair,making hair look smooth,shiny and healthy.• When a bee or red ant stings us, it injects acidic liquid intoour body.We can neutralise the acid by rubbing the stingswith calamine lotion,which contains alkali. This will stop thepain.
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