Topic 4: Chemical changes

Question 1

what happens in a displacement reaction?

Answer 1

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

Question 2

which non-metals are also included in the reactivity series?

Answer 2

hydrogen and carbon

Question 3

what determines how reactive a metal is?

Answer 3

how easily they lose electrons- forming positive ions, the higher up the reactivity series a metal is the more easily they lose electrons

Question 4

what is the order of the reactivity series?

Answer 4

potassium, sodium, lithium, calcium, magnesium, carbon, zinc, iron, hydrogen, copper

Question 5

zinc + hydrochloric acid –>

Answer 5

zinc chloride + hydrogen

because the zinc is more reactive than the hydrogen

Question 6

what happens when magnesium reacts with dilute acid?

Answer 6

lots of bubbles are given off telling us that magnesium reacts vigorously

Question 7

what is oxidation?

Answer 7

gain of oxygen

eg 2Mg + O2 –> 2MgO

Question 8

what is reduction?

Answer 8

loss of oxygen

eg 2CuO + C –> 2Cu + CO2

Question 9

copper + hydrochloric acid –>

Answer 9

copper + hydrochloric acid

as the copper is less reactive than thew hydrogen

Question 10

what are metals found as?

Answer 10

unreactive metals like gold are found in the Earth as the metal itself but most metals are found as compounds that require chemical reactions to extract the metal

Question 11

how can you extract metals less reactive than carbon?

Answer 11

by reduction with carbon

Question 12

what is the process of electrolysis?

Answer 12

when an ionic compound is melted or dissolved in water the ions are free to move about within the liquid or solution. These solutions are able to conduct electricity and are called electrolytes.
passing current through electrolytes causes the ions to move the electrolytes. positively charged ions move to the negative electrode (the cathode) and negative ions move to the positive electrode (the anode). Ions are discharged at the electrodes producing elements.

Question 13

if lead bromide is electrolysis what will be produced at the + and - electrode?

Answer 13

\+ = bromine
- = lead

Question 14

when can electrolysis be used and why does it use large amounts of energy?

Answer 14

1) metals can be extracted from molten compounds using electrolysis. electrolysis is used if the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon
2) large amounts of energy are used in the extraction process to melt the compounds and product electrical currents

Question 15

how do you prepare aluminum for electrolysis?

Answer 15

you make a molten mixture of aluminum oxide and crytolite using carbon as the positive electrode (anode)

Question 16

why should a mixture be used and why does the anode have to be constantly replaced?

Answer 16

a mixture is used because this allows the ions something to move in

the electrode must be replaced because the oxygen from aluminum oxide reacts with the carbon it is made out of producing aluminum oxide therefore wearing away the carbon

Question 17

what happens at the cathode and anode?

Answer 17

at the cathode positively charged ions gain electrons and so the reactions are reduction
at the anode negatively charged ions lose electrons and so the reactions are oxidations

Question 18

what is half equation for reduction with hydrogen?

Answer 18

2H2+ +2e- –> H2

Question 19

what is the half equation for oxidation with hydroxide?

Answer 19

4OH- + 4e- –> O2 + 2H20

Question 20

what is oxidation and reduction?

Answer 20

oxidation = loss of electrons
reduction = gain of electrons

roses are red,
GCSE’s give me pain,
Oxidation is loss,
Whilst reduction is gain, (going to get a 9 in English)

Question 21

what happens at the anode and cathode when an aqueous solution is electrolysis?

Answer 21

cathode:
hydrogen is produced if the metal is more reactive

anode:
oxygen i produced unless the solution contains halide ions (group 7 ions)

This happens because in the aqueous solution water molecules break down producing hydrogen ions and hydroxide ions that are discharged

Question 22

what do some acid react with metal to make?

Answer 22

salt and hydrogen

Question 23

what forms when a acid reacts with an alkali?

Answer 23

water and salt

Question 24

what forms when a acid reacts with and metal carbonates?

Answer 24

salt, water and carbon dioxide

Question 25

what is the PH scale measured in, what does it measure and what is it measured with?

Answer 25

• 0 to 14
• how acidic/ alkali a solution is
• universal indicator

Question 26

what PH is an acid, alkali and neutral solution?

Answer 26

acid: less than 7
alkali: more than 7
neutral: 7