Acids and Alkalis

• The Ph Scale shows how acidic a substance is

• Acids and Alkalis can be measured using a PH metre

• Ph can also be measures using an indicator

1 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15

0 → very acidic

7 → neutral

14 → very alkaline

The PH scale classifies solutions as acidic, alkali or neutral

Neutral solutions are exactly pH7 [substance that is not acidic or alkaline]

Acidic solutions have a Ph of less than 7 and the closer they are to 0 the more acidic they are

Alkaline solutions have a Ph of more than 7 and the more closer they are to 14 the more alkaline they are

You can find the Ph of s sybstance in 2 ways:

A ph metre: A ph metre gives a numerical value of the ph.

An indicator:An indicator is a substance that changes colour depending on the pH of the solution it is mixed with.

Some indicators are liquids, so we can add drops of the indicator to the solution being tested. Other indicators are strips of paper, and we can dip these into the solution.

Litmus is an example of an indicator. It turns red in solutions that are acidic and it is blue in alkaline solutions.

Universal indicator is a special indicator because it turns into a different colour at many different pH values.

Reactions of metals with acids

• Acids react with most metals.

• When an acid reacts with a metal, the products are a salt and hydrogen.

• This is the general word equation for the reaction: metal + acid → salt + hydrogen

When a metal reacts with an acid you can see bubbles being produced and the metal getting smaller.

Hydrochloric acid → chloride

Nitric acid → nitrate

Sulfuric acid → sulfate

The table below has some more examples.

Example : magnesium + sulfuric acid → magnesium sulfate + hydrogen

Or a symbol equation:

Mg + H₂SO₄ → MgSO₄ + H₂