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 – HNO 3 –Sulfuric Acid – H 2 SO 4 –Citric Acid – HC 6 H 7 O –Acetic Acid – HC 2 H 3 O 2

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 – NH 4 OH –Sodium bicarbonate – NaHCO 3

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  H 2 O + NaCl –H 2 SO 4 + 2KOH  2H 2 O + K 2 SO 4 –H 3 PO 4 + Al(OH) 3  3H 2 O + AlPO 4

The End…For Now!