Acids, bases and salt

Learning objectives:

to learn how to choose the appropriate method for making a salt and learn how acids and alkalis result in a neutralization reaction 

Acids have a pH less than seven and bases have a pH greater than 7. The pH scale runs from 1-14. When bases are dissolved in water they are known as alkalis.
Salts are formed when acids react with bases , of which the name depends on the given base or acid.

Acids turn universal indicator red and turn blue litmus paper red. Bases will usually react with acids to form a salt and water.

Strong acids will totally dissociate in water, which means they will produce H+ ions, where as weak acids only partly dissociate, this means that less H+ ions will be produced.

Alkalis are bases that dissolve in water. They turn red litmus paper blue and universal indicator purple.

Neutralization reactions

When acids dissolve in water they produce hydrogen ions
For example

HCl H+ + Cl –

When alkalis dissolve in water they produce hydroxide ions

For example

NaOH OH- + Na+

When the H+ ions react with the OH- ions they produce water or H2O

Salt

When acids react with bases, salt and water are formed

Acid + metal oxide salt + water
Acid + metal hydroxide salt + water

When naming salts the alkali gives the first half of the name and the acid forms the second half

e.g. sulfuric acid will form sulfates
Sodium hydroxide will form sodium salts

Making soluble salts

When a base dissolves in water, you can add an acid to neutralize the solution. Warming the salt solution can evaporate away the water leaving only the salt crystals

Some bases do not dissolve in water, for these bases, you will need to filter away the excess un dissolved parts and the evaporate the water

Making insoluble salts

As insoluble salts do not dissolve in water, mixing appropriate solutions of ions together can make them
In order to make an insoluble salt, you can react together two soluble salts in a precipitate reaction

For example
Silver nitrate and sodium chloride are both soluble. When you mix them together you form a soluble sodium nitrate but an insoluble silver chloride, the sodium chloride will appear as a precipitate.

An equation for this is

AgNO3 + NaCl NaNO3 + AgCl

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