Selasa, 25 November 2008


Acids And Bases

A chemical compound which dissociates (ionises) to produce hydrogen ion (or
hydroxonium ion), when dissolve in water.
• Example of acids
@ hydrochloric acid
@ nitric acid
•Acid is a proton donor.
•Monoprotic acid
@one molecule of an acid dissociates in water to produce one hydrogen ion.
•Diprotic acid
@ one molecule of acid dissociates in water to produce two hydrogen ions.

Properties of an acid
Physical properties
•Taste sour @ Is corrosive
•Turns blue litmus paper red @ Has a pH value below than 7
•Conducts electricity
Chemical properties
•Reacts with reactive metal such as Magnesium, Mg, aluminium, Al, zinc, Zn, iron, Fe, to release hydrogen gas.
•React with carbonate such as calcium carbonate to release carbon dioxide.
•Reacts with a base to form salt and water.
•Neutralises an alkaline solution to form salt and water only.

•A chemical compound that can react with acid to form salt and water.
@ sodium oxide @ sodium hydroxide crystals
@ potassium hydroxide solution @ sodium hydroxide solution
@ calcium hydroxide solution @ ammonia solution
•Not all bases can dissolve in water. A base that dissolves in water is called an alkali.
•A base that is not dissolve in water will remain as a base.
Application of acids and alkalis in daily life
•Carbonic acid is used to manufacture soft drinks.
•Vinegar contains ethanoic acid and can be used as food preservatives.
•Sulphuric acid is used as an electrolyte in car batteries.
•Methanoic acid solidifies latex.
•Hydrochloric acid is used to remove rust
•Yoghurt contains lactic acid.

Examples of applications of alkalis in daily life.
•Soaps and detergents contain sodium hydroxide.
•Toothpaste contains magnesium hydroxide (weak alkali).
•Gastric pills contain aluminium hydroxide or magnesium hydroxide (weak alkali).
•Ammonia solution is used to make chemical fertilisers and prevent solidification of latex.
•Calcium hydroxide is used to make cement.

Properties of alkali
Physical properties
•Taste bitter and feels smooth @ Is corrosive
•Turns red litmus paper blue @ Has a pH value of above 7
•Conducts electricity
Chemical properties
•Reacts with ammonium salt such as ammonium chloride to produce salt, water and ammonia gas when heated.
•Neutralise an acidic solution to form salt and water.

Concentration of Acid and Alkali
Concentration of the solution
•The measurement which show the quantity of the dissolved solute in 1dm^3
of the solution.
•Unit : g dm^-3 / mol dm^-3
•Formula ( g dm^- 3) :
mass of solute (g) / volume of solution (dm^3)
•Formula ( mol dm^-3)
= number of mole of solute (mol) / volume of solution (dm^-3)
•Concentration of a solution measured in mol dm^-3.
•The unit of the concentration that shows the number of moles of a solute that dissolves in 1 dm^3 of solution.
molarity = number of moles of solute / volume of solution in dm^3

Relationship between number of moles with molarity and volume of solution.
MV / 1000 = number of moles
Where M = Molarity of solution ( mol dm^-3)
V = Volume of solution (cm^3)

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