Topic 3 - Chemical Changes

Question 1

What is the pH scale?

Answer 1

A measure on how acidic or alkaline a solution is

Ranges fro 0-14

Question 2

How can you measure the pH of a solution?

Answer 2

Using an indicator and comparing what colour that shows up on the periodic table

Question 3

What do acids and bases do together?

Answer 3

They neutralise each other

Question 4

How can neutralisation reactions be shown?

Answer 4

As an ionic equation

Question 5

Acids produce what ions in water?

Answer 5

Hydrogen ions

Question 6

Acids can be strong or what?

Answer 6

Weak

Question 7

What are strong acids?

Answer 7

e.g. hydrochloric, sulfuric, nitric

Ionise almost completely in water. They tend to have low pHs (0-2)

Question 8

What are weak acids?

Answer 8

e.g. citric, carbonic acids

Do not fully ionise in solution. Only a small proportion of the acid molecules. Their pHs tend to be around 2-6

Question 9

What is the difference between a strong and concentrated acid?

Answer 9

The acid strength tells you what proportion of acid molecules ionise the water

The concentration tells you how much acid there is within a litre (1 dm^3) of water. Concentration is how watered down your acid is.

Question 10

Can you have a dilute strong acid?

Answer 10

Yes

The acid can be watered down, so there is less acid per dm^3, however it can be strong in terms of the proportion of acid molecules using the pH scale

Question 11

Salts form when acids react with what?

Answer 11

Bases

Question 12

What are salts?

Answer 12

Ionic compounds

Question 13

A salt is formed in what type of reaction?

Answer 13

A neutralisation reaction

Question 14

Acid + metal oxide -> salt + water

Give some examples

Answer 14

2HCl + NaOH -> NaCl +H2O

H2SO4 + ZnO -> ZnSO4 +H2O

Question 15

Acid + metal hydroxide -> salt + water

Give some examples

Answer 15

HCl + NaOH -> NaCl +H2O

H2SO4 + Zn(OH)2 -> ZnSO4 + 2H2O

Question 16

Acid + metal -> salt and hydrogen

Give an example

Answer 16

2HCl + Mg -> MgCl2 +H2

Question 17

How do you test for hydrogen?

Answer 17

Using a light splint. A popping sound should be heard

Question 18

Acid + metal carbonate -> salt + water + carbon dioxide

Give an example

Answer 18

2HCl + Na2CO3 -> WNaCl + H2O + CO2

Question 19

What is the test for carbon dioxide

Answer 19

Using limewater. If carbon dioxide is present, the limewater will turn cloudy

Question 20

How do you make soluble salts?

Answer 20

By reacting an acid with an alkali

Question 21

What is oxidation?

Answer 21

Oxidation is the loss of electrons, but gain of oxygen

Question 22

What is reduction?

Answer 22

The gain of electrons but the loss of oxygen

Question 23

What is electrolysis?

Answer 23

The breaking down of a substance using electricity

An electric current is passed through the electrolyte, causing it to decompose

Question 24

What do half equations show?

Answer 24

How electrons are transferred during reactions

Question 25

What are cations, and where do they go during electrolysis?

Answer 25

Positive ions. They move towards the cathode (negative electrode) and become reduced

Question 26

What are anions, and where do they go during electrolysis?

Answer 26

Negative ions. They move towards the anode (positive electrolyte) and are oxidised

Question 27

In molten ionic solutions, there’s only one source of ions. True or false?

Answer 27

True They can be electrolysed because the ions can move freely and conduct electricity

Question 28

Why is hydrogen gas sometimes form in electrolysis?

Answer 28

In aqueous solutions, H+ and metal ions will be present. Hydrogen gas will be produced if the metal is more reactive than hydrogen If the metal is less reactive than hydrogen, a solid layer of pure metal is formed