C3.3

Question 1

What are redox reactions in terms of oxygen?

Answer 1

A redox reaction is a reaction in which reduction and oxidation happen at the same time.

Question 2

What is reduction in terms of oxygen

Answer 2

It is the loss of oxygen from a substance

Question 3

What is oxidation in terms of oxygen

Answer 3

It is the gain of oxygen from a substance

Question 4

How are 2 steel railways welded together, ready for trains to run on them less than an hour later

Answer 4

The thermite reaction.
This reaction produces molten iron which runs into a small gap between the rails.
The iron cools and solidifies and is then machined to a smooth finish

Question 5

What happens in the reaction
Aluminium + iron (III) —> aluminium oxide + iron
2Al+ Fe2O3 —> Al2O3 + 2Fe (I)

Answer 5

Aluminium gains oxygen and is oxidised to aluminium oxide. At the same time iron loses oxygen and is reduced to iron. Overall, oxygen is transferred from iron to aluminium
Aluminium acts as a reducing agent because it reduces iron oxide to iron.
Iron oxide acts as an oxidising agent because it oxidises aluminium to aluminium oxide

Question 6

A thermite reaction includes…

Answer 6

Aluminium and iron (iii) oxide.

Question 7

What does a half equation show?

Answer 7

A half equation shows the change that happens to one reactant in a reaction.

Question 8

What is an acid?

Answer 8

An acid is a substance that releases hydrogen ions, H+, when it dissolves in water to make an aqueous solution.

Question 9

What is a base

Answer 9

A base is a substance that can neutralise acids.

Question 10

What are alkalis?

Answer 10

Water soluble bases

An alkali releases hydroxide ions OH- when it dissolves in water.

Question 11

What is the pH scale?

Answer 11

The pH of a solution describes its relative acidity of alkalinity.

Question 12

pH of an alkaline = ?

Answer 12

More than 7

>7

Question 13

pH of an acid

Answer 13

Less than 7

<7

Question 14

What is universal indicator ?

Answer 14

Universal indicator is a mixed indicator. It contains different indicators that change colour over different pH ranges.

Question 15

What is neutralisation

Answer 15

Neutralisation is the reaction between an acid and a base to form a salt and water

ACID + BASE —> SALT + WATER

Question 16

how do you predict the salt made?

Answer 16

The names of salts have 2 parts

1. The first part comes from the metal in the base or alkali
2. The second part of the name comes from the acid used.

Question 17

What happens during neutralisation in solution?

Answer 17

Acidic solutions contain hydrogen ions and alkaline solutions contain hydroxide ions. These react together during neutralisation to make water
(H+ + OH- —> H2O)

The salt produced depends on the other ions present

Question 18

What are carbonates?

Answer 18

Carbonates are ionic compounds that contain the carbonate ion (CO3)2-

Question 19

What happens when acids react with carbonates

Answer 19

Acid + carbonate —> salt + water + carbon dioxide

Question 20

What happens during this reaction between calcium carbonate and dilute hydrochloric acid?

CaCO3 + 2HCl —> CaCl2 + H2O + Co2

Answer 20

The carbon dioxide is released as bubbles in the acid during the reaction.
Calcium carbonate is insoluble in water but calcium chloride (the salt formed) is soluble in water.
This is why a lump of calcium carbonate appears to dissolve if you add acid to it.

Question 21

What happens when acids react with metals

Answer 21

If a metal reacts with a dilute acid the reaction produces a salt and hydrogen

ACID + METAL —> SALT + HYDROGEN

Question 22

What happens in the reaction between magnesium and dilute hydrochloric acid?

Mg + 2HCl —> MgCl2 + H2

Answer 22

The hydrogen is released as bubbles in the acid. As the reaction goes on, soluble magnesium chloride forms. This is why a piece of magnesium ribbon appears to dissolve if you put it into acid, even through magnesium itself is insoluble

Question 23

Carbon dioxide is given off from carbonates reacting with acids

Answer 23

!!

Question 24

Hydrogen is produced by and metal if it reacts with water or with an acid

Answer 24

..

Question 25

What is a dilute acid

Answer 25

It contains a low ratio of acid to volume of a solution

Question 26

What is a concentrated acid

Answer 26

It contains a high ratio of acid to volume of solution

Question 27

What are weak acids

Answer 27

Weak acids Are partially ionised

Only a small amount of their molecules release H+ ions

Question 28

What are strong acids?

Answer 28

They are fully ionised

All of their molecules release H+ ions

Question 29

What does —>

Answer 29

The reaction does not go to completion

Question 30

How is pH linked to hydrogen concentration

Answer 30

In an aqueous solution, as the concentration of H+ ions increases by 10, the pH decreases by 1.

This means…
An acid has a lower pH when it is concentrated than when it is dilute

A strong acid has a lower pH than a weak acid at the same concentration,

Question 31

What does oxidised mean (electron and oxygen)

Answer 31

It describes a substance that has gained oxygen or lost oxygen in a chemical reaction

Question 32

What is an oxidising agent? (Oxygen and electrons)

Answer 32

A substance that oxidises another substance by donating oxygen or by accepting electrons