Chapter 7ACIDS AND

BASES

What is acid?

a substance that ionizes in water to produce hydrogen ions, H+

What is base?

a substance that reacts with an acid to form only salt and water

What is alkali?

Soluble bases that produce OH¯ ions in water

Chemical properties of acid Sour taste pH less than 7 Corrosive Conduct electricityAcid can react with a) bases to produce salts and water b) metals to produce salts and hydrogen gas c) carbonates to produce salts , carbon

dioxide gas and water

Chemical properties of base

Bitter/smooth/soapy pH more than 7 Corrosive Conduct electricityBase can react with a)Acid to produce a salt and water b)Heated with ammonium salt to produce

ammonia gasvideo

Uses of acids in daily lifeSulphuric acid – paints, detegents, polymers,

fertilisersCarbonic acid- make carbonated drinksEthanoic acid- vinegar

Uses of base in daily lifeSodium hydroxide – soaps, detergents,

bleaching agentsMagnesium hydroxide – toothpasteAmmonia- fertilisers

Role of water in the formation of hydrogen ions

In the presence of water, an acid will ionize to form the hydrogen ions, H +

So, water is essential for the formation of hydrogen ions that cause acidity

Role of water in the formation of hydroxide ions

In the presence of water, alkali will dissociate to form hydroxide ions, OH¯

Hence, water is essential for the formation of hydroxide ions that cause alkalinity

pH scale

A set of numbers used to show the degree of acidity and alkalinity of a solution

pH values of less than 7 indicates an acidic solution

pH values of more than 7 indicates an alkaline solution

pH values of 7 indicates a neutral solution

pH values

Higher pH value more alkalinehigher concentration of hydroxide ion

Lower pH value more acidichigher concentration of hydrogen ion

When acids meets base

• pH is actually a measurement of the concentration of hydrogen, H+ in a solution

• The higher the concentration of the H+

ions, the lower the pH value, and more acidic the solution is

• The higher the concentration of the OH¯ ions, the higher the pH value and the more alkaline solution the solution is.

Acid

Strong acid is an acid that dissociate (ionize ) completely in water to form hydrogen ion,H+ of high concentration

Weak acid is an acid that dissociate (ionize ) partially in water to produce hydrogen ions,H+

of low concentration.

• Mineral acids such as hydrochloric acid, nitric acid, and sulphuric acid are strong acids

• Weak acids-ethanoic acid, methanoic acid, citric acid, tartaric acid

Alkali

Strong alkali is produce when a base dissociates completely in water to produce hydroxide ions, OH- of high concentration

Weak alkali is produced when a base dissociates partially to produce hydroxide ions, OH- of low concentration.

• Strong alkali- sodium hydroxide, potassium hydroxide

• Weak alkali- ammonia solution

EDITED BY :

Noor Laili binti Mohamad EliasD20091034948

ISMP KIMIA 2009/2010

Thank you