Acid, bases and salts

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CuO + H2SO4 ------------- CuSO4 + H2O

These metal oxides tend to be ionic in bonding character with high melting points.

As you move left to right the oxides become less basic and more acidic.

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TYPES OF OXIDES

ACIDIC OXIDES: On the right of the Periodic Table the acidic oxides of the non-metals are present e.g. CO2, P2O5, SO2, SO3 etc.

These tend to be covalent in bonding character with low melting/boiling points.

Those of sulphur and phosphorus are very soluble in water to give acidic solutions which can be neutralised by alkalis to form salts.

SO2 + H2O ----------- H2SO3

SO3 + H2O ----------- H2SO4

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TYPES OF OXIDES

AMPHOTERIC OXIDES:

They are metallic oxides.

They react with both acids and alkalis.

They are usually relatively insoluble and have little effect on indicators.

An example is aluminium oxide dissolves in acids to form 'normal' aluminium salts like the chloride, sulphate and nitrate. However, it also dissolves in strong alkali's like sodium hydroxide solution to form 'aluminate' salts.

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TYPES OF OXIDES

NEUTRAL OXIDES:

They are non- metallic oxides.

They tend to be of low solubility in water and have no effect on litmus.

do not react with acids or alkalis. eg CO carbon monoxide and NO nitrogen monoxide, H2O.

There is no way of simply predicting this kind of behavior from periodic table patterns!

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Periodic trends in oxides

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Salts

When H+ ion of an acid is replaced by a metal ion, a salt is produced e.g.

H2SO4(aq) + 2NaOH(aq) ====== Na2SO4(aq) + 2H2O(l)

Here sodium sulphate (Na2SO4) is the salt formed. Salts are ionic compounds.

Note: Ammonia (NH3) is an unusual base - it does not contain a metal. It forms ammonium salts, containing the ammonium ion, NH4+.

e.g. NH3(aq) + HNO3(aq)  NH4NO3(aq) (ammonium nitrate)

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Methods of making Soluble Salts

ACID + METAL  SALT + HYDROGEN

2) ACID + BASE  SALT + WATER

3) ACID + CARBONATE  SALT + WATER + CARBON DIOXIDE

ACID + ALKALI  SALT + WATER

DIRECT COMBINATION

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Method 1 (Acid + Metal)

Not suitable for making salts of metals above magnesium, or below iron/tin in reactivity.

e.g.