Paper 1 Priority

Question 1

Chlorine and thiosulphate

Answer 1

4Cl2 + S2O3 2- + 5H20 -> 8Cl- + 2SO4 2- + 10H+

Question 2

Thiosulphate and iodine

Answer 2

I2 + 2S2O3 2- -> 2I - + S4O6 2-

Question 3

Test for hydrogen halide

Answer 3

React with ammonia

White smoke

Of NH4X

Doesn’t distinguish between them

Question 4

Ammonium ion test

Answer 4

NH4 + + OH- -> NH3 + H20

Which turns damp red litmus blue from ammonia gas

When dipped in HCl and held in the gas, white smoke of ammonium chloride is observed

Question 5

When should water appear in the Kc expression

Answer 5

When water is in the gaseous state it should appear

When it is reactant but not solvent it should appear

If it is a solvent, even if also reactant or product, it should not appear - constant concentration

Question 6

Acidic buffer solution

Alkali buffet solution

Answer 6

Acidic- weak acid and conjugate base
Alkaline - weak base and conjugate acid

Must be more than 0.05 moldm^-3 but less than a factor of ten

Question 7

Buffer regions in titration curves

Answer 7

Start of a weak acid and adding strong base

Or start of strong acid added to weak base

Question 8

Factors that affect the hydration enthalpy

Answer 8

The larger the magnitude of the charge on the ion, the higher the magnitude of the hydration enthalpy

The larger the radius of the ion the less exothermic the hydration enthalpy

Question 9

LnK

Answer 9

Δs total = RlnK

ΔG = -RTlnk

Lnk is proportional to ECell

Question 10

Cell diagram

Answer 10

Formula of metallic anode followed by vertical line
Ions present in the anode area followed by two vertical lines
Ions present in the cathode area followed by a vertical line
The formula of the metallic cathode

Question 11

Principles of storage cells

Answer 11

Chemical reactions at both electrodes must be able to be reserved when electrical potential is applied
The oxides and reduced forms of the anode and cathode must be solid

Question 12

Acidic hydrogen electrode

Answer 12

Polymer electrolyte membrane

H+ ions move through it

Question 13

Alkaline hydrogen electrode

Answer 13

Porous platinum electrodes
Aqueous solution of potassium hydroxide electrolyte

CO2 In air reduces efficiency
KOH can leak out

Still more efficient than PEM cells

Question 14

Hydrogen fuel cells environmental issues

Answer 14

Hydrogen produced by electrolysis which consumes a lot of energy originally from fossil fuels

Hydrogen can explode/ hard to store

Methane possible alternative

Question 15

Ethanol fuel celll

Answer 15

C2H5OH + H20 reversible CH3COOH + 4H+ + 4e-

O2 + 4H+ + 4e- reversible 2H20

Can be made by fermenting sugar

Uses agriculture land

Question 16

Isomerism in transition metals

Answer 16

Cis trans occurs in octahedral and square planar complexes not not tetrahedral

Optical occurs with bidentate ligands

Question 17

Oxidation of Cr3+ to CrO4 2-

Answer 17

Hydrogen peroxide in alkaline solution