Chemistry

Acids + Bases

Acids

• Acids are corrosive substances - they react with solid substances ‘eating them away‘

• Some acids like sulphuric acid are used in car batteries. Sulphuric acid is also dangerously corrosive

• Some acids are safe to even taste like the ones in fruit and vinegar

• Strong acids are able to react to their full extent with other substances, while weak acids do not.

• The word acid comes from the latin word ‘acidus’ meaning sour.

Bases

• Some bases are very corrosive especially caustic soda (sodium hydroxide)

• Bases that can be dissolved in water are called alkalis

• Similar to acids bases can be strong or weak

• The strength of an acid or base can be measured by the pH scale.

How do you tell if a substance is an acid or a base?

• Acid base indicators are substances that can be used to tell whether a substance is an acid or a base.

• They react with acids and bases producing different colour in each

• 1 commonly used indicators:

  • Litmus - turns red in acid and blue in a base

  • Bromothymol blue - turns yellow in acid and blueish purple in a base

  • Universal indicator - a mixture of indicators and it changes colour as the strength of an acid or base changes.

    

The pH scale

• You can describe how acidic or basic a substance is by using the numbers on pH scale

• The pH scale ranges from 0-14

• Low pH numbers (less than pH 7) mean that the substance is acidic

• High pH numbers (more that pH 7) mean that the substance is basic

• If a substance has a pH of 7, it is said to be neutral - neither acidic not basic

• Pure water is an example of a neutral substance

• The pH scale also measures whether an acid or base is strong or weak

• A strong acid has a very low pH (pH 0 or 1)

• A strong base has a very high pH (pH 14 or 15)

Neutralisation

• When an acid and a base react to eachother, the products include water and a salt a reaction like this is called a nautralisation

• Neutralisation reactions are also used to cooking and to keep swimming pools and spas clean

• To neutralise means to stop something from having an effect.

• To stop the properties of acids from having an effect, a base can be added to it.

• To stop a bas from having an effect, an acid can be added.

acid + base → water + salt