C4 - Chemical Changes

Question 1

Name all elements in the REACTIVITY SERIES from MOST REACTIVE to LEAST

Answer 1

Potassium
Sodium
Calcium
Magnesium
Aluminium
(CARBON)
Zinc
Iron
Tin
Lead
(HYDROGEN)
Copper
Silver
Gold
Platinum

Question 2

When will a DISPLACEMENT REACTION occur?

Answer 2

A displacement reaction occurs when a more reactive metal displaces a less reactive metal from a compound.

e.g, Zn + CuSO4 -> ZnSO4 + Cu

Question 3

What displaces HYDROGEN?

Answer 3

Group 1 metals are more reactive than hydrogen so they displace it.

Question 4

What is formed when a GROUP 1 METAL DISPLACES HYDROGEN?

Answer 4

Hydrogen gas and a metal hydroxide.

Question 5

What can we utilise DISPLACEMENT REACTIONS for?

Answer 5

We can utilise displacement to obtain metals from their ores, by displacing with a more reactive less valuable metal/carbon.

e.g, FeO can be displaced with Carbon to produce Fe. ( IRON OXIDE is REDUCED )

Question 6

What is OILRIG?

Answer 6

Oxidation
Is
Loss

Reduction
Is
Gain

Question 7

Example of how to write HALF EQUATIONS

Answer 7

If Na (Sodium) is oxidised , it has lost an electron, leaving it with a 1+ charge, so the half equation is;

Na -> Na+ + e-

If Na 1+ ion is reduced, it has gained an electron, leaving it with a charge of 0, so the half equation is:

Na+ + e- -> Na

Question 8

What did CHARGES on each side of a HALF EQUATION add up to?

Answer 8

Both sides should add up to the same number.

Question 9

What happens when an ACID and an ALKALI react?

Answer 9

When an ACID (pH < 7) reacts with an ALKALI (pH > 7), a salt and water (pH = 7), if reacted completely.

Question 10

What happens when an ACID and an ALKALI react? (EQUATION)

Answer 10

Acid + Alkali -> Salt + Water

e.g, HCl + NaOH -> NaCl + H20

Question 11

What is the SALT dependant on in an alkali/base reaction?

Answer 11

The salt produced depends on the acid.
OR
The positive ions in the alkali/base.

Question 12

Name the 3 ACIDS and SALTS

Answer 12

Hydrochloric Acid –> Chlorides (XCl)
Nitric Acid –> Nitrates (XNO3)
Sulfuric Acid –> Sulphates (XSO4)

Question 13

How can CRYSTALS be obtained from a dissolved salt?

Answer 13

Obtainable of a dissolved salt by heating gently so that the water evaporates, leaving any salt behind.

Question 14

What is produced when an ACID and a METAL react?

Answer 14

A salt and hydrogen are produced.

Question 15

What is produced when an ACID and a METAL react? (EQUATION)

Answer 15

Acid + Metal -> Salt + Hydrogen

e.g 2HCl + Mg -> MgCl2 + H2

Question 16

What type of reaction occurs when an ACID and a METAL react?

Answer 16

REDOX reaction - one substance is reduced, the other is oxidised.

Question 17

What pH does an ALKALI have?

Answer 17

pH > 7, due to OH- ions

Question 18

What pH does an ACID have?

Answer 18

pH < 7, due to H+ ions

Question 19

What pH does H2O have?

Answer 19

H2O is neutral (pH=7).
Equal number of H+ and OH- ions.

Question 20

What is the pH dependant on?

Answer 20

pH is dependant on the concentration of H+/OH- ions.

Question 21

What does UNIVERSAL INDICATOR do?

Answer 21

Provides an indication of what pH an element/compound is.

Question 22

Describe the properties of a STRONG ACID

Answer 22

Completely IONISED in aqueous solution.

Question 23

Describe the properties of a WEAK ACID

Answer 23

Partially IONISED in an aqueous solution.

Question 24

IF AN ACID IS STRONGER…

Answer 24

THE pH IS LOWER

Question 25

Name 3 examples of a STRONG ACID

Answer 25

Hydrochloric
Nitric
Sulfuric

Question 26

Name 3 examples of a WEAK ACID

Answer 26

Ethanoic
Carbonic
Citric

Question 27

Describe the process of ELECTROLYSIS

Answer 27

Involves passing an electrical current through a substance to cause oxidation and reduction at both electrodes; ANODE and CATHODE.

Question 28

When does ELECTROLYSIS occur?

Answer 28

Can only happen if the ions are free to move to the electrode they’re attracted to.

Question 29

When can ELECTROLYSIS OCCUR in IONIC COMPOUNDS?

Answer 29

In IONIC COMPOUNDS, electrolysis can only happen when molten or in a solution.

Question 30

What can ELECTROLYSIS be used to OBTAIN?

Answer 30

Can be used to obtain pure metals from a compound/ore.

Question 31

Describe the process of ELECTROLYSIS of a SIMPLE IONIC COMPOUND

Answer 31

When a simple ionic compound is electrolysed in the molten state using inert electrodes, the metal is produced at the CATHODE, and the non-metal is produced at the ANODE.

Question 32

Describe the process of USING ELECTROLYSIS to EXTRACT METALS

Answer 32

-Metals that are TOO REACTIVE to be reduced by carbon are extracted via electrolysis.
-Large amounts of energy are utilised in the extraction process to melt the compounds.
-Anodes have to be replaced as oxygen that is formed reacts with the carbon of the electrode to form carbon dioxide.

Question 33

What is used during ELECTROLYSIS to reduce cost of melting METALS/COMPOUNDS?

Answer 33

Some metals/compounds have VERY high melting points, and so CRYOLITE is used to reduce the cost of this.

Question 34

Describe the process of ELECTROLYSIS of SOLUTIONS

Answer 34

-At the CATHODE, hydrogen is produced, unless the metal is less reactive than hydrogen, then the metal is produced at the CATHODE, and hydrogen stays in the solution.

HALF EQUATION FOR FORMATION OF HYDROGEN;
2H+ + 2e- –> H2

-At the ANODE, if halide ions are present, then one of the halide ions is OXIDISED at the ANODE.

Question 35

What are HALIDE IONS?

Answer 35

F-, Cl-, Br-

Question 36

What happens if HALIDE IONS aren’t present during ELECTROLYSIS?

Answer 36

If no HALIDE IONS are present, oxygen is OXIDISED instead, forming OXYGEN GAS.