C5: Chemical Changes

Question 1

What happens when different metals react with oxygen?

Answer 1

Group 1/2 metals - vigorous reactions
Transition metals - slow reactions

Question 2

What is the general equation of metals reacting with oxygen?

Answer 2

metal + oxygen → metal oxide

Question 3

What is oxidation?

Answer 3

The gaining of oxygen
or the loss of electrons

Question 4

What is reduction?

Answer 4

The loss of oxygen
or the gain of electrons

Question 5

What is the general equation for group 1 metals reacting with water?

Answer 5

metal + water → metal hydroxide + hydrogen

Question 6

Where do hydrogen and carbon go in the reactivity series?

Answer 6

Carbon - between magnesium and zinc
Hydrogen - between iron and copper

Question 7

How can inert metals be extracted from their ores?

Answer 7

They already come in their pure form because they’re so unreactive

Question 8

How can relatively reactive metals be extracted from their ores?

Answer 8

Displacement - a more reactive metal will displace the less reactive metal and remove it from its ore form
(carbon is usually used if it’s more reactive because it’s much cheaper)

Question 9

What is the state symbol usually associated with acids?

Answer 9

aq

Question 10

What happens to acids in aqueous solutions?

Answer 10

Produce a H+ ion

Question 11

What are bases usually?

Answer 11

Metal oxides or metal hydroxides (or metal carbonates)

Question 12

What are alkalis?

Answer 12

Bases which are soluble in water

Question 13

What happens to alkalis in aqueous solituons?

Answer 13

They produce OH- ions

Question 14

What does the pH scale show?

Answer 14

The acidity or the alkalinity of a solution

Question 15

How can we determine the pH of a solution?

Answer 15

pH probe
Universal indicator
Litmus paper

Question 16

What is the general equation for a neutralisation?

Answer 16

acid + base → salt + water
(H+ from acid and OH- from alkali react to produce water,
more general is H+ + OH- → H2O)

Question 17

What is the general equation for acids reacting with metals?

Answer 17

acid + metal → salt + hydrogen

Question 18

How does the reactivity of a metal affect how quickly it reacts with an acid?

Answer 18

The more reactive it is, the faster it reacts as it displaces hydrogen more quickly

Question 19

Give an example of an oxidation and reduction equation in relation to acids reacting with metals

Answer 19

2HCl + Mg → MgCl2 + H2
Oxidation = Mg → Mg2+ + 2e
Reduction = 2H+ + 2e → H2

Question 20

What are the products when acids react with metal carbonates?

Answer 20

salt + water + carbon dioxide

Question 21

What is the difference between strong and weak acids?

Answer 21

Weak acids partially dissociate when dissolved in water, strong acids fully dissociate in water

Question 22

What are examples for the equations for the ionisation for weak and strong acids?

Answer 22

Strong = HCl →H+ + Cl -
Weak = H2CO2 → H+ + HCO3-
←

Question 23

What are 3 examples of weak acids?

Answer 23

Carbonic acid
Ethanoic acid
Citric acid

Question 24

What does the pH scale tell about the concentration of H+ ions in acids?

Answer 24

Strong acids have a lower pH for a given concentration, as they produce a greater conc. of hydrogen ions

Question 25

What is the pattern followed by the pH scale?

Answer 25

As the pH scale decreases by 1 unit, the concentration of hydrogen ions increases by 10 times
e.g. pH 1 has a 10x greater conc. of H+ than pH 2

Question 26

Describe the process of carrying out a titration

Answer 26

Use a pipette to transfer 25cm³ of the alkali into a conical flask (reduces risk of splashing). Add 5 drops of indicator to the conical flask and place the flask on a white tile. Fill a burette with sulfuric acid, and place the conical flask under the burette. Slowly release the acid from the burette until a colour change is seen (swirl the conical flask while doing so)

Question 27

How do you calculate a titre?

Answer 27

New amount - staring amount