C5 - Chemical Changes

Question 1

Oxidation

Answer 1

• adding oxygen to an element

Question 2

What is reduction?

Answer 2

Removing oxygen from an element

Question 3

Electrons in terms of oxidation and reduction

Answer 3

When an element is oxidised, it loses electrons
When an element gains electrons it is reduced

Question 4

What kind of ions do metals form?

Answer 4

Positive ions

Question 5

What are metal ores?

Answer 5

• naturally occurring mineral from which a metal can be extracted economically
• metals are present as positive ions in a compound
• need to be reduced
• chemically (displacement with a more reactive metal) or electrically (electrolysis)

Question 6

What is considered before metal ores are extracted?

Answer 6

• whether it is economically viable
• how much metal it contains
• demand for metal
• how easy it is

Metals are present as positive ions in a compound.
Need to be reduced.
Chemically (displacement) or electrically (electrolysis)

Question 7

The pH scale

Answer 7

• how acidic or alkaline a solution is
• pH scale goes from 0 to 14
• less than 7 = acid - lower, the more acidic
• more than 7 = alkali
• neutral substances = pH 7

Question 8

Testing pH

Answer 8

• one way to test pH is using an indicator
• an indicator is a dye that changes colour depending on whether it’s above or below a certain pH
• some indicators contain a mixture of dyes that mean they gradually change colour over a broad range of pHs - these are a wide range of indicators
• they’re useful for estimating the pH of a solution
• universal indicator

Another method is to use a pH probe attached to a pH meter which can measure pH electronically
A probe

Question 9

Acids

Answer 9

• substances that produce H+ ions when in aqueous solution - must contain hydrogen
• bases = anything which is OH- ions - must contain hydroxide
• bases are substances which dissolve acids
• all alkalis = bases