Acid, Bases and Salts

Question 1

What are alkalis?

Answer 1

These are soluble bases with a ph above 7. They neutralise acids

Question 2

What are acids?

Answer 2

Substances with a pH below 7.

Question 3

How is hydrochloric acid formed?

Answer 3

When the gas hydrogen chloride dissolves in water

Question 4

What do we mean by ‘aqueous’?

Answer 4

A substance dissolved in water that can be acidic, alkaline or neutral depending on the substance.

Question 5

What causes acidity?

Answer 5

H+ ions cause acidity.

All acids form H+(hydrogen ions) when we add them to water

Question 6

What causes a substance to be alkaline?

Answer 6

OH- ions( hydroxide ions). All alkalis form hydroxide ions when we add them to water.

Question 7

What are indicators?

Answer 7

Indicators are substances that change colour when we add them to acids and alkalis

E.g litmus paper

Question 8

What is universal indicator?

Answer 8

This is a combination of dyes which can give us an estimate of the pH of a solution.

Question 9

Why are pH sensors sometimes good?

Answer 9

It is more precise and it is not subject to inter observer bias( people won’t have different interpretations).

Question 10

How can we make soluble salts?( method 1)

Answer 10

Acid+ metal. However this can only occur if the metal is more reactive than hydrogen. If it is the metal will react with the acid to form a salt and hydrogen gas.

Can usually see bubbles with this reaction

Question 11

How can we make soluble salts?( method 2)

Answer 11

Acid + insoluble base
Salt and water is formed from this.

This is known as a neutralisation reaction and it can also be described as

(H+) + (OH-) = H2O

The salt made depends on the metal or the base that we use, as well as the acid. For e.g bases that contain sodium ions will always make sodium salts

The salt formed depends on the acid used
When we use hydrochloric acid( HCL), the salt formed is always a chloride
Sulphuric acid( H2SO4)= sulfates
Nitric acid(HNO3)= nitrates

Question 12

Describe an experiment making soluble salts

Answer 12

Example: making a copper salt( copper sulfate crystals)

1) Add copper oxide( an insoluble base) to sulphuric acid and stir. Warm gently on a tripod and gauze
Do not let it boil.

2) The solution should turn blue as the reaction occurs, indicating that copper sulfate is being formed. Keep adding copper oxide until an excess can be seen( to make sure everything’s completely reacted)
3) When the reaction is complete, filter the solution to remove excess copper oxide.
4) We can then evaporate the water by heating it , so that crystals of copper sulfate start to form. Stop heating when you see the first crystals appear at the edge of the solution.

Finally leave to evaporate slowly so larger crystals will form.

Question 13

How do we make insoluble salts?

Answer 13

By reacting solutions of two soluble salts together.

Question 14

Why are indicators used in reactions between acids and alkalis?

Answer 14

To show when the acid and alkali have completely reacted to produce the salt solutions

Question 15

What are bases?

Answer 15

Bases( which include alkalis) are substances that can neutralise acids. Metal oxides and metal hydroxides are bases. They have a pH above 7

Question 16

Give an example of the reaction between soluble salts solutions to make an insoluble salt

Answer 16

For example: we add potassium iodide solution to lead nitrate solution in a beaker and stir.

The precipitate of lead iodide that forms is filtered from the solution.

The precipitate is washed with distilled water to make sure that all the potassium nitrate( the other product of the reaction) is washed away and it is then dried on fresh filter paper.

Extras: you filter by putting a folded piece of filter paper in a filter funnel and stick into comical flask

When pouring the contents of the beaker into the middle of filter paper, make sure it is above the filter paper or solid could go down the side.

Rinse contents of beaker with distilled water to make sure you got all the product from beaker

Question 17

What does an acid and metal carbonate equal?

Answer 17

Salt,water and carbon dioxide.

Question 18

How do we use precipitate reactions?

Answer 18

Remove pollutants from wastewater that are produced by factories.

The effluent must be treated before it is discharged into reviews and seas.
-Also used to remove metal ions from industrial waste water( increase pH of water so insoluble metal hydroxides precipitate out). Produces a sludge which can easily be removed from the solution.

Precipitation used to remove unwanted ions from drinking water

Question 19

What are the solubility rules?

Answer 19

All group 1 metals are soluble
Ammonium salts are soluble
Nitrates are soluble
Halide ions are soluble ( except with lead, silver or Mercury)

Sulfites, carbonates and phosphates insoluble
Hydroxide compounds are insoluble ( except for with alkali metals and barium and calcium)
Oxides are usually insoluble.

Question 20

How do we make ammonium salts?

Answer 20

React ammonia solution with an acid until there is a small excess of ammonia. We can detect this excess ammonia with universal indicator. We then crystallise the ammonium salt from the solution and the excess ammonia evaporates off.

As well as the ammonium salt, water is formed.

E.g nitric acid to form ammonium nitrate( NH4NO3) and water.
Ammonium nitrate used as a fertiliser.

Question 21

What is crystallisation?

Answer 21

Crystallisation is a separation technique that is used to separate
a solid that has dissolved in a liquid and made a solution.