Acids & Bases

What is an Acid?• Acids are substances that dissociate (fall apart into

ions) in water to form hydrogen ions (H+).• Acids are:

– Sour-tasting.– Water-soluble (aqueous).– Very reactive.– Ionic compounds.

• Acids will usually start with hydrogen at the beginning of their formulas.

• Common acids include:– Hydrochloric Acid – HCl– Nitric Acid – HNO3

– Sulfuric Acid – H2SO4

– Citric Acid – HC6H7O– Acetic Acid – HC2H3O2

What is a Base?• Bases are substances that accept the hydrogen ions

(H+) that acids form. Bases, like acids, dissociate in water.Another word for a substance that acts as a base is alkaline.

• Bases are:– Bitter-tasting.– Water-soluble (aqueous).– Very reactive.– Ionic compounds.

• Many bases, but not all, will end with the hydroxide ion (OH-).

• Common bases include:– Sodium hydroxide – NaOH– Calcium hydroxide – Ca(OH)2

– Potassium hydroxide - KOH– Ammonium hydroxide – NH4OH– Sodium bicarbonate – NaHCO3

The pH Scale

• The pH scale provides chemists with a way of measuring the strength of an acid or base.

• pH stands for “portenz of hydrogen” – which means “strength of hydrogen”.

• The pH scale ranges from 0 – 14.

• A pH value of 7 is right in the middle of this and it represents a perfectly neutral pH – neither acid nor base – like pure water.

The pH Scale• Acids go from 7 to 0 on

the pH scale. Acids get more and more stronger as you get closer to 0.

• Bases go from 7 to 14 on the pH scale. Bases get more and more stronger as you get closer to 14.

• Each step on the pH scale means you are changing the strength by 10 times.

Acid-Base Indicators• An acid-base indicator is any substance that changes

colour in the presence of an acid or a base.• Litmus – a plant extract – is the most widely known and

used acid-base indicator.• Litmus turns red in the presence of acids• Litmus turns blue in the presence of bases.• Universal indicators show a different colour for many pH

values. They often come in the form of pH paper which contains many different acid-base indicators in it.

Neutralization Reactions• A neutralization reaction occurs when an

acid and a base undergo a double displacement reaction to form water and a salt (ionic compound).

• The general equation for a neutralization is:Acid + Base Water + Salt

• It is called a neutralization reaction because the effects of the acid and the base cancel each other out to make water.

• Examples:– NaOH + HCl H2O + NaCl– H2SO4 + 2KOH 2H2O + K2SO4

– H3PO4 + Al(OH)3 3H2O + AlPO4

• The End…For Now!