Topic 9/19

Question 1

Which cell potential is oxidized?

Answer 1

The more negative

Question 2

Formula for cell potential

Answer 2

Cathode (red) - anode (oxi)

Question 3

Is more reactive metal oxidized or reduced?

Answer 3

Oxidized (can lose electrons easier)

Question 4

What sign do cell potential and gibbs need to be for spontaneous reaction?

Answer 4

positive and negative

Question 5

Products formed from the electrolysis of soidum chloride dilute and concentrated

Answer 5

ANODE
Dilute: 2H2O = O2 + 4H+ + 4e
Conc: 2Cl- + Cl2 + 2e

CATHODE
2H2O + 2e = H2 + 2OH-

Question 6

Products formed from the electrolysis of copper II sulphate with graphite electrodes

Answer 6

ANODE
2H2O = 4H+ + O2 + 4e

CATHODE
Cu2+ + 2e = Cu

Question 7

Products formed from the electrolysis of copper II sulphate with copper electrodes

Answer 7

ANODE
Cu = Cu2+ + 2e

CATHODE
Cu2+ + 2e = Cu

Question 8

Products formed from the electrolysis of water

Answer 8

ANODE
2H2O = 4H+ + O2 + 4e

CATHODE
2H2O + 2e = H2 + 2OH-

Question 9

What is BOD

Answer 9

amount of oxygen used to decompose organic matter in water

Question 10

Molar ratio of products in the wrinkler method

Answer 10

1 mol O2 → 2 mol of I2 → 4 mol of S2O32−

Question 11

How to calculate concentration of dissolved oxygen with Wrinkler method

Answer 11

Mols of oxygen using ratio (1:4) and then divide by volume of water (25cm^3)

Question 12

Why should Wrinkler method be done at a constant temperatuer?

Answer 12

Rate of reaction of oxygen with impurities depends on temperature

Question 13

Voltaic cell vs electrolytic cell energy supply

Answer 13

Voltmeter and battery

Question 14

Conditions for SHE electrode

Answer 14

hydrogen gas at 298K and 100kPa, 1 moldm^3 H+ and platinum electrode

Question 15

Which conditions deposit the greatest mass of copper?

Answer 15

Low charge but high current

Question 16

Concentrated vs dilute salt products electrolysis

Answer 16

Negative H2
Positive - conc is gas but dilute is O2

Question 17

Products of electrolysis of if molten potassium chloride

Answer 17

Anode - Cl2
Cathode: K

Question 18

How to figure out mass of product deposited in electrolysis?

0.59 Ni desposited how much Ag?

Answer 18

Find moles of ni and then do molar ratio of electrons of ni to ag when balanced and then multiply by the molar mass to find the mass

Question 19

Calculate 5 day BOD in mg dm^-3

Answer 19

1. BOD (mols) = day 1 - day 5
2. moldm^-3 = BOD/volume of water
3. mg dm^-3 = (2) x molar mass (32g) x 1000

Question 20

Products of the electrolysis of dilute copper (ii) chloride

Answer 20

Anode: oxygen gas
Cathode: copper (s)

Question 21

Is standard electrode potential negative or positive for spontaneous reaction?

Answer 21

Pos

Question 22

Does entropy increase or decrease for the following reaction?

2(aq) = 1(s) + 1(aq)

Answer 22

Decreases, two mols aq to one mol aqueous

Question 23

What does low BOD mean?

Answer 23

low levels of water pollution