C2.6 - Acids, Bases and Salts

Question 1

What is the pH scale?

Answer 1

The pH scale measures how acidic or alkaline a solution is. A low pH means that a solution is acidic. A high pH means that a solution is alkaline.

Question 2

What pH does pure water have?

Answer 2

Pure water has a pH of 7.

Question 3

What is an acid?

Answer 3

An acid is a liquid that contains more Hydrogen ions (H+) than Hydroxide ions(-OH). It has a pH of less than 7.

Question 4

What is an alkali?

Answer 4

An alkali is a liquid that contains more Hydroxide ions (-OH) than Hydrogen ions (H+). They are soluble bases. It has a pH of more than 7.

Question 5

What is a base?

Answer 5

A base is a substance with a pH greater than 7.

Question 6

What is the reaction between acids and bases called?

Answer 6

The reaction between acids and bases is called neutralisation. It occurs when the right amounts of acid and alkali cancel out to form a salt and water (which is neutral).

Question 7

What is the equation for neutralisation?

Answer 7

Acid + Base -> Salt + Water

Question 8

What does an indicator do?

Answer 8

An indicator can indicate that a neutralisation reaction is over – the colour it changes to is dependent on the pH of the substance.

Question 9

What does (s) mean?

Answer 9

Solid

Question 10

What does (l) mean?

Answer 10

Liquid

Question 11

What does (g) mean?

Answer 11

Gas

Question 12

What does (aq) mean?

Answer 12

Dissolved in water

Question 13

What do salts contain?

Answer 13

Salts contain a metal part and a non-metal part.

Question 14

What are insoluble salts?

Answer 14

Insoluble salts do not dissolve in water - they have the symbol (s).

Question 15

What are soluble salts?

Answer 15

Soluble salts dissolve in water - they have the symbol (aq).

Question 16

What are the rules for naming salts?

Answer 16

The first part of the salt’s name is the metal.

The second part of the salt’s name depends on the acid used.

Question 17

What is the equation for an acid plus a metal?

Answer 17

Acid + Metal -> Salt + Hydrogen

Question 18

Acids will do what with hydrogen?

Answer 18

Acids will react with metals that are above hydrogen in the reactivity series.

Question 19

How can we know that a reaction between a metal and an acid is finished?

Answer 19

At some point, the acid has all reacted.

If we add more metal then it will not react.

This shows us that the reaction is finished.

Question 20

How do we get the salt from a metal + acid equation?

Answer 20

We have an unreactive metal left over from adding it to find out if the reaction finished.

We filter off the unreactive metal to leave a solution of the salt.

We evaporate the water to crystalise the salt.

Question 21

What metals cannot be made safely?

Answer 21

Reactive metals, such as sodium, cannot be made safely due to their violent reactions.

Question 22

Why can’t metals like gold react?

Answer 22

Other metals, such as gold, are too unreactive and will not react with acids.

Question 23

How can we know that a reaction between an acid and a base has finished?

Answer 23

Once the acid has all reacted, if we add more base then it will not react. Instead, it will simply sink. This shows us that the reaction is finished.

Question 24

How do we get the salt from an acid + base reaction?

Answer 24

We have to filter out the unreactive base.

We evaporate the water to crystalise the salt.

Question 25

What do we always make from an acid + alkali reaction?

Answer 25

We always make a soluble salt (salt + water).

Question 26

How can we know that a reaction between an acid and an alkali has finished?

Answer 26

We use a pH indicator to find the pH of the solution. When the pH is 7, the reaction has finished.

Question 27

Why can't we filter the products of an acid and an alkali reaction?

Answer 27

We make a solution - we cannot filter it.

Question 28

How do we get the salt from an acid + alkali reaction?

Answer 28

Once the pH is neutral, we evaporate the water to crystalise the salt.

Question 29

Explain how ammonium nitrate is made.

Answer 29

Ammonia dissolves in water to make an alkaline solution. To make it into a neutral salt, it reacts with nitric acid to produce ammonium nitrate. No water is produced. The salt can be obtained from the solution by evaporation and crystallisation.

Question 30

Why is ammonium nitrate useful?

Answer 30

Ammonium nitrate is a good fertiliser because it has nitrogen from two sources - from ammonia and nitric acid. Plants need nitrogen to produce amino acids.

Question 31

How do we make an insoluble salt?

Answer 31

If we want an insoluble salt, we can use a precipitation reaction.

Question 32

What is a precipitate?

Answer 32

A precipitate is a solid formed when two solutions are mixed together. We can separate this by filtration.

Question 33

How do we perform a precipitation reaction?

Answer 33

Find the two solutions that contain the ions required. (For lead chloride you need lead ions and chloride ions) Mix these together. Once completed, filter it from the solution, wash it, and dry it on filter paper. This is to remove any of the unwanted solution.

Question 34

How are precipitation reactions useful?

Answer 34

Precipitation reactions can be used to remove poisonous ions (lead) from drinking water. The water is treated by adding substances that react with the pollutant metal ions dissolved in the water to make insoluble salts.

Question 35

What is the chemical formula for hydrochloric acid?

Answer 35

HCl

Question 36

What is the chemical formula for sulfuric acid?

Answer 36

H2SO4

Question 37

What is the chemical formula for nitric acid?

Answer 37

HN03