p2. chemical changes

Question 1

what is electrolysis?

Answer 1

• when an ionic compound is melted or dissolved in water
• ions are free to move about the liquid or solution
• liquids or solutions ( electrolytes ) are able to conduct electricity

Question 2

what is the negative electrode?

Answer 2

• the cathode

Question 3

what is the positive electrode?

Answer 3

• the anode

Question 4

what is the negative ion?

Answer 4

• anion

Question 5

what is the positive ion?

Answer 5

• cation

Question 6

describe the process of electrolysis

Answer 6

• passing electric current through electrolytes which causes the ions to move to electrodes
• positively charged ions move to the negative electrode ( cation to cathode )
• negatively charged ions move to the positive electrode ( anions to anode )
• ions are then discharged at electrodes producing elements

Question 7

main stages in half equations

Answer 7

• form an ion back to original atom
  eg . Na+ + e- = Na

Question 8

describe the process of electrolysis in molten ionic compounds

Answer 8

• simple ionic compound electrolysed in molten state
• metal produced at cathode
• non-metal produced at anode

Question 9

how can electrolysis be used to extract metals?

Answer 9

• used if metal is too reactive to be extracted by reduction of carbon or if metal reacts with carbon
• large amounts of energy used in extraction process to melt compounds and produce electrical current

Question 10

why can the positive electrode must be continually replaced?

Answer 10

• positive anode is made up of carbon
• which reacts with oxygen to produce carbon dioxide
• must be replaced

Question 11

what is produced at both the anodes and cathodes during electrolysis aqueous solutions?

Answer 11

• anodes = oxygen is produced if solution contains an ion
• cathodes = hydrogen is produced if metal is more reactive

Question 12

RP. investigate what happens when aqueous solutions are electrolysed

Answer 12

1. answer scientific question to develop hypothesis
2. using measuring cylinder,measure 40ml of electrolyte into a beaker
3. place two graphite rods into electrolyte - attaching one electrode to negative terminal of a dc supply , and the other electrode to the positive terminal
4. place two test tubes over each electrode to collect any gasses produced
5. turn on power supply and observe what happens
6. test any gas produced by holding piece of blue litmus next to electrode
7. record observations and result of test
8. rinse electrochemical cell apparatus and collect new electrodes to try with new electrolyte

Question 13

how to identify reduction and oxidation

Answer 13

• reduction = at cathode,positively charged ions gain electrons
• oxidation = at anode,negatively charged ions lose electrons