Chemical Changes

Question 1

What happens when metals react with other substances?

Answer 1

The metal atoms form positive ions.

Question 2

What is the order of the reactivity series?

Answer 2

1. Potassium
2. Sodium
3. Litium
4. Calcium
5. Magnesium
6. Carbon
7. Zinc
8. Iron
9. Hydrogen
10. Copper

Question 3

Which and how are the most reactive metals extracted?

Answer 3

Extracted by using electrolysis.
› potassium (K)
› sodium (Na)
› lithium (Li)
› calcium (Ca)
› magnesium (Mg)

Question 4

Which and how are the least reactive metals extracted?

Answer 4

Extracted by reduction with carbon.
› zinc (Zn)
› iron (Fe)
› hydrogen (H)
› copper (Cu)

Question 5

What is oxidation?

Answer 5

It means gain of oxygen and the loss of electrons.
E.g. magnesium can be oxidised to make magnesium oxide.

[used for the formation of metal]

Question 6

What is reduction?

Answer 6

It means the gain of electrons and loss of oxygen.
E.g. copper oxide can be reduced to copper.

[used for the extraction of metal]

Question 7

What do acids react with to form salts and water?

Answer 7

Metals.
E.g. acid + metal oxide → salt + water.
acid + metal hydroxide → salt + water.

Question 8

Describe a neutralisation reaction.

Answer 8

› the reaction between acids and bases.
↳ acid + base → salt + water.
› neutralisation between acids and alkalis can be seen in terms of H⁺ and OH⁻ ions.
↳ H⁺₍𝖺𝘲₎ + OH⁻ ₍𝖺𝘲₎ → H₂O₍𝑙₎.
› when an acid neutralises a base (or vice versa), the products are neutral so they have a pH of 7.
↳ this could e shown using an indicator.

Question 9

Describe what the pH scale is used to measure.

Answer 9

The pH scale is used to measure how acidic or alkaline a solution is.
↳ the lower the pH of a solution, the more acidic it is (red) between 0 - 6.
↳ the higher the pH of solution, the more alkaline it is (purple) between 8 -14.
› a neutral substance such as pure water has pH 7.

Question 10

Describe the use of universal indicator to measure approximate pH of a solution.

Answer 10

Universal indicator is used to estimate the pH of a solution because it can turn a variety of colours.

Question 11

What can a more reactive metal do to a less reactive metal from a compound?

Answer 11

A more reactive metal displaces a less reactive metal from a compound.

Question 12

Where are unreactive metals and metals found?

Answer 12

UNREACTIVE METALS such as gold are found in the Earth as the metal itself.
METALS are found as compounds that require chemical reactions to extract the metal.

Question 13

What do these produce?

a. hydrochloric acid.
b. nitric acid.
c. sulphuric acid.

Answer 13

a) hydrochloric acid produces chlorides.
b) nitric acid produces nitrates.
c) sulphuric acid produces sulphates.

Question 14

How can soluble salts be made?

Answer 14

From acids by reacting them with solid insoluble substances such as metals, metal oxides, hydroxides or carbonates.
⟶ the solid is added to the acid until no more reacts.
↳ the excess solid is filtered off to produce a solution of the salt.
↳ salt solutions can be crystallised to produce solid salts.

Question 15

What are strong acids?

Answer 15

An acid that completely ionises in water to produce hydrogen ions.

[e.g hydrochloric acid, sulphuric acid, nitric acid]

Question 16

What are weak acids?

Answer 16

An acid that partially ionises in water to produce hydrogen ions.

[e.g. ethanoic acid, citric acid, carbonic acid]

Question 17

What happens as the pH decreases per one unit?

Answer 17

The hydrogen ion concentration of the solution increases by a factor of 10.

Question 18

What is the process of electrolysis?

Answer 18

When positively charged ions move to the negative electrode (the cathode) and negatively charged ions move to the positive electrode (the anode). Ions are discharged at the electrodes producing elements.

Question 19

When is electrolysis used?

Answer 19

If the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon.

Question 20

How is aluminium manufactured?

Answer 20

The electrolysis of a molten mixture of aluminium oxide and cryolite using carbon and the positive electrode (anode).

Question 21

What is the connection between cathodes and anodes and reductions and oxidations?

Answer 21

› at the cathode (negative electrode), positively charged ions gain electrons and so reaction are reductions.
› at the anode (positive electrode), negatively charged ion lose electrons and so the reactions are oxidation.

Question 22

What are the two ways to measure pH?

Answer 22

> universal indicator.

> pH probe.

Question 23

What is the use of a pH probe?

Answer 23

Gives an accurate value of the pH.

Question 24

What is acid strength?

Answer 24

A measure of the proportion of acid molecules that ionise in water.

Question 25

What is acid concentration?

Answer 25

A measure of the number of acid molecules in a certain volume of water.

Question 26

What does metal + oxygen produce when they react?

Answer 26

Metal oxide.

Question 27

What does metal + acid produce when they react?

Answer 27

Salt + hydrogen.

Question 28

What does metal + water produce when they react?

Answer 28

Metal hydroxide + hydrogen.

Question 29

What is a displacement reaction?

Answer 29

When a more reactive element displaces a less reactive metal from its compound.

Question 30

What is a redox reaction?

Answer 30

Where one substance in a reaction is reduced and another is oxidised.