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Which drink do you prefer— lemonade or sweet tea?
One is a weak acid and the other a weak alkali.
If not for some sweetener, the lemonade would be a sour-tasting acid, and the tea a bitter-tasting alkali. Any substance that can be dissolved in water is either acidic or alkaline or, if neither, then neutral.
There are many different sorts of acids. 
Carbonated lemonade contains carbonic acid, and the hydrochloric acid in your stomach helps to digest your food.
Car batteries are filled with sulfuric acid. Although these are all acids, they are not all the same strength. Carbonic acid is very weak and sulfuric acid is very strong. If you fill a car battery with lemonade, it certainly won't make enough electricity to start the engine!

There are also strong and weak alkalis.

Bicarbonate of soda (baking soda) is a weak alkali used in cooking.
Sodium hydroxide is a strong alkali that can clean baked-on grease from inside ovens. Scientists use an indicator to test the strength of an acid or an alkali. They add the indicator to a few drops of the substance they want to test. The color of the indicator changes. The color is checked against a color chart.
This shows pH numbers between 1 and 14.

What is pH value?

A pH (potential of hydrogen) number indicates the concentration of hydrogen ions in a solution.
Strong acids are pH 1.
They become weaker as the number rises to pH 6.
Neutral substances are pH 7—neither acidic nor alkaline.
Weak alkalis are pH8. They become stronger as the number rises to pH 14.

Balancing acids with alkalis

When you add an acid to an alkali, the alkaline substance and the acid balance each other out. Scientists say they neutralize each other. People can get indigestion pains when there is too much acid in their stomachs. Look at a packet of indigestion tablets. You'll see they contain bicarbonate of soda, also called baking soda or sodium bicarbonate.
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