Chemistry GCSE: C4 Chemical Changes

Question 1

What pHs do alkalis have?

Which pH is the most alkali?

Answer 1

Alkalis have pHs above (greater than) 7

pH 14 is the most alkali

Question 2

What pHs do acids have?

Which pH is the most acidic?

Answer 2

Acids have pHs below 7

pH 0 is the most acidic

Question 3

What pH is neutral?

Answer 3

pH7

Question 4

Give two ways that you can measure the pH of a substance.

Say which is better and why?

Answer 4

Universal indicator or a pH probe

A probe gives a more precise (and accurate) reading.

Question 5

What colour does universal indicator go in

Strong acids

Weak acids

Answer 5

Strong acids: Red

Weak acids: Orange/yellow

Question 6

What colour does universal indicator go in

Strong alkalis

Weak alkalis

Answer 6

Strong alkalis: Purple

Weak alkalis: Blue

Question 7

What colour does universal indicator go in

Neutral solutions

Answer 7

Neutral solutions: Green

Question 8

What type of ions do alkalis contain

Answer 8

Hydroxide ions (OH^-)

Question 9

What type of ions do acids contain

Answer 9

Hydrogen ions (H⁺)

Question 10

What is the difference between alkalis and bases?

Answer 10

Alkalis are bases that dissolve in water

Question 11

What do we call reactions between acids and alkalis/bases?

Answer 11

Neutralisation reactions

Question 12

Why does adding acids and alkalis/bases together lead to neutralisation?

Answer 12

Because the hydrogen ions react with the hydroxide ions to make water.

H⁺ + OH^- => H₂O

Question 13

Metal oxides (e.g magnesium oxide) are bases. What two other types of compunds are bases?

Answer 13

Metal hydroxides (e.g sodium hydroxide) and metal carbonates (e.g calcium carbonate).

Question 14

What two things are made when metals react with acids?

Complete this reaction: Sulfuric acid + magnesium =>

Answer 14

A salt and hydrogen

Sulfuric acid + magnesium => magnesium sulfate + hydrogen

Question 15

What two things are made when metal oxides or metal hydroxides react with acids?

Complete this reaction: Hydrochloric acid + iron oxide =>

Answer 15

A salt and water

Hydrochloric acid + iron oxide => iron chloride (a salt) + water

Question 16

What three things are made when metal carbonates react with acids?

Complete this reaction: Nitric acid + calcium carbonate =>

Answer 16

A salt, water and carbon dioxide

Nitric acid + calcium carbonate => calcium nitrate + water + carbon dioxide

Question 17

What types of salts are made using hydrochloric acid?

Answer 17

Chlorides (e.g calcium chloride)

Question 18

What types of salts are made using nitric acid?

Answer 18

Nitrates (e.g copper nitrate)

Question 19

What types of salts are made using sulfuric acid?

Answer 19

Sulfates (e.g iron sulfate)

Question 20

Put these metals in order or their reactivity: Potassium, magnesium, lithium, calcium, sodium.

Explain how you worked this out

Click here for the periodic table

Answer 20

Potassium, lithium sodium, calcium, magnesium.

Group 1 elements first (from bottom to top).

Group 2 elements next (from bottom to top)

Question 21

Learn the order of reactivity of the following elements. Cover the list and see if you can remember it.

• Carbon (most reactive)
• Zinc
• Iron
• Hydrogen
• Copper (least reactive)

Answer 21

• Carbon (most reactive)
• Zinc
• Iron
• Hydrogen
• Copper (least reactive)

Question 22

What two things are made when metals react with water?

Complete the following equation: Magnesium + water =>

Answer 22

Metal hydroxides and hydrogen

Magnesium + water => Magnesium hydroxide and hydrogen

Question 23

Name two metals that are found as pure metals.

Why are these metals found as pure metals?

Answer 23

Gold and silver

Because they are very unreactive.

Question 24

Most metals are not found as pure metals, they are found as metal ores. What type of compounds are metal ores.

Answer 24

Metal ores are metal oxides.

Question 25

What two methods can be used to extract metals such as iron from their metal ores/oxides?

Answer 25

Displacement using carbon Electrolysis

Question 26

Why can carbon be used to extract zinc, iron and copper from their ores/oxides?

Answer 26

Beacuse carbon more reactive than zinc, iron, copper and so will displace them.

Question 27

Why can't carbon be used to extract aluminium from its ore/oxide?

Answer 27

Because carbon is less reactive than aluminium.

Question 28

Why are zinc, iron and copper extracted using carbon (displacement) instead of using electrlysis?

Answer 28

Electrlysis is much more expensive because.... Melting metal ores uses lots of energy Creating an electric current uses lots of energy

Question 29

In electrolysis, what is the charge of the anode and what is the charge of the cathode? PANIC

Answer 29

**P**ositive **A**node **C**athode **I**s **N**egtive

Question 30

Whay does electrlysis mean? What is it used for?

Answer 30

Using electricity (electro) to break things up (lysis). Breaking up ionic compunds into their elements.

Question 31

In what state do ionic compounds have to be for electrolysis.

Answer 31

**Liquid**/molten or **aqueous**/dissolved/in a solution

Question 32

What does aqueous mean

Answer 32

It means that the substance is dissolved in water/in a solution.

Question 33

In electrolysis, which electrode do the non-metal ions go to? Explain why

Answer 33

Non-metal ions go to the anode (positive electrode) Non-metals ions have a negative charge so are attracted to the positive anode.

Question 34

In electrolysis, which electrode do the metal ions go to? Explain why

Answer 34

Metal ions go to the cathode (negative electrode) Metals ions have a positive charge so are attracted to the negative cathode.

Question 35

In electrolysis, what happen to negative ions when they arrive at the anode (positive electrode)?

Answer 35

They **lose electrons** and are **discharged** as atoms or molecules.

Question 36

In electrolysis, what happen to positive ions when they arrive at the cathode (negative electrode)?

Answer 36

They **gain electrons** and are **discharged** as atoms or molecules.

Question 37

What is oxidation?

Answer 37

When a substance gains oxygen (e.g if carbon gains oxygen to become carbon dioxide the carbon has been oxidised). Higher tier: When a subtance loses electrons (OIL RIG: Oxidation is loss, reduction is gain).