Electricity and Chemistry

Question 1

Why ions conduct as solution or molten rather than solid (2)

Answer 1

ions held tightly in ionic lattice when solid

lattice breaks once solution/molten + ions are free to move

Question 1

Define electrolysis

Answer 1

breakdown of ionic compound using electricity

Question 2

What electrolytic cells contain (3)

Answer 2

molten or aqueous electrolyte (ionic compound being broken down)

battery/powerpack

electrodes referred to as anode or cathode (usually made of graphite or platinum)

Question 3

Why are anodes or cathodes made of graphite/platinum

Answer 3

will not react

Question 4

What is the anode connected to

Answer 4

positive terminal of battery

Question 5

What is the cathode connected to

Answer 5

negative terminal of battery

Question 6

Stages of Electrolysis (4)

Answer 6

ionic compound made molten or aqueous

electric current passed through cell from anode to cathode

cations attracted to cathode - gain electrons (reduction)

anions attracted to anode - lose electrons (oxidation)

Question 7

Electrolysis for dilute sulfuric acid (2)

Answer 7

cathode product : hydrogen

anode : oxygen

Question 8

Observations for electrolysis of dilute sulfuric acid (2)

Answer 8

hydrogen + oxygen tests

colourless gas at both electrodes

Question 9

Electrolysis for Molten Lead Bromide (2)

Answer 9

cathode : lead

anode : bromine

Question 10

Observations for electrolysis of molten lead bromide (2)

Answer 10

silvery solid at cathode

brown gas at anode

Question 11

Why is the anode in electrolysis positively charged

Answer 11

electrons flow from anode to positive terminal of battery

Question 12

Why is the cathode in electrolysis negatively charged

Answer 12

electrons flow from negative terminal to cathode

Question 13

Electrolysis of concentrated NaCl (Brine) (2)

Answer 13

cathode : hydrogen

anode : chlorine

Question 14

Observations of electrolysis of concentrated NaCl (2)

Answer 14

colourless gas at cathode

pale yellow gas at anode

Question 15

Why does the cathode produces hydrogen instead of sodium in the electrolysis of concentrated NaCl (2)

Answer 15

sodium ions (Na^+) not easily reduced, hydrogen ions (H^+) from water reduced at cathode

sodium ion reacts with OH^- left from H2O –> forms sodium hydroxide

Question 16

How do you predict the product formed at the cathode in electrolysis (with water) (2)

Answer 16

metal above hydrogen in reactivity series = H+ ions reduce + hydrogen gas formed

metal below hydrogen in reactivity series = metal ions reduce

Question 17

How do you predict the product formed at the anode in electrolysis (3)

Answer 17

electrochemical series

if Cl-, Br-, or I- present = element will form at anode

if group ions present with oxygen = oxygen will form

Question 18

Define electroplating

Answer 18

piece of one metal is coated in thin layer of other material

Question 19

Purpose of electroplating (2)

Answer 19

prevent corrosion

improve appearance

Question 20

Explain the process of electroplating (5)

Answer 20

cathode = object to be electroplated

anode = metal placed on object

electrolyte solution = salt with ions of metal plated on object

metal anode experiences oxidation - dissolves + replaces ions in solution

metal ions in solution experience reduction at cathode - form metal atoms + coat object

Question 21

Electrolysis of Copper (II) sulfate (2)

Answer 21

Copper (II) ions reduced at cathode - forms copper at electrode

anode = oxygen gas formed

Question 22

Electrolysis/Extraction of Aluminum (5)

Answer 22

impurities from bauxite removed to give aluminum oxide

aluminum oxide dissolved in molten cryolite (different ore of aluminum) - to lower melting point

carbon cathode line tank - Al3+ ions move there + reduced to Al atoms

O^2- ions move to anode - become oxidised to form oxygen + react with carbon to produce carbon dioxide

carbon anodes need to regularly be replaced