Paper 1 errors

What type of compound of magnesium can be used as an “antacid” and why

insoluble strong base - Mg(OH)2

the mols that you calculate enthalpy change of neutralisation are..

mols of H2O formed

A graph of ln(k) is plotted against 1 / T for a reaction.

(k = rate constant, T = temperature in K.)
The gradient has the numerical value of –16 000.
What is the activation energy, in kJ mol–1, for this reaction?

A +1.92
B +133
C +1920
D +133 000

B. ea = gradient / -8.314

turn to kj = / 1000

Define the term lattice enthalpy

The amount of energy released when one mole of ionic lattice is formed from its gaseous ions

at RTP, ionic lattice is almost always

solid

Explain using collision theory, how the gradient of conc / time decreases over time

concentration decreases, so collisions are less frequent

In an equilibrium, the total gaseous mols on each side must..

be equal

Why ar the bond angles in SO3 120? (1)

3 bonding REGIONS, no lone electron pairs

Why do SO2 and SO3 have polar bonds, but only SO2 has polar molecules (2)

Polar bonds because difference in electronegativity between S and O

Only SO2 has polar molecules due to lone pair of electrons, assymetrial molecule and non-linear / charges not dispersed evenly, and dipoles don’t cancel

State the approximation that means that you can form [H+][A-] into [H+]²

[H+] = [A-]

[H+] / disassociation from water is negligible

1. Sea water contains aqueous bromide ions.

   Chlorine is used to extract bromine from sea water.

   Construct the ionic equation for this reaction and explain why chlorine is suitable for this extraction of bromine but iodine is not. (2)

Cl2 + 2Br- → Br2 + 2Cl-

Chlorine is a stronger oxidising agent than bromine, but bromine is a stronger oxidising agent than iodine.

Explain P4s and S8s low boiling points

P4 and S8 have the lowest boiling point because they are simple molecular structure and strong covalent bonding. Only have weak induced dipole-dipole forces between them, which are easy to break. S8 has a higher melting point because it has more electrons, therefore London forces are stronger, and require more energy to break

‘Standard electrode” refers to…

Element’s half-cell compared to H2

Standard electrode potential definition

The voltage of half cell measured against standard hydrogen electrode under standard conditions

how to get from Ba(OH)2 to Ba(Cl)2

acid base reaction

Ba(OH)2 + 2HCl → 2H2O + Ba(Cl)1

explain, using ligand substitution, how haemoglobin transports oxygen around the body

1. lone pair from O is donated to / forms coordinate / dative bonds with Fe2+

2. O can reversibly substitute with / be replaced by H2O and CO2

Which compound has polar molecules and why

HCN

BCl3

CO2

C2F4

HCN because it is assymetrical and uneven distribution of charge

percentage dissacociation of methanoic acid 0.015 mol dm3, Ka = 1.6×10-4

[H+] = Root of Ka x [HA] = 1.549×10-3

percentage dissociatoin = ans / 0/015 × 100

Which substances have induced dipole-dipole interactions in their solid state and why

C2H6, H2O, Si

All but silicone, because silicone is a giant covalent lattice, which do not have london forces. Onlty simple molecular compounds do

If you hae a diatomic atom being atomised, what do you need to do to the enthalpy change

x 2

why is lattice enthalpy always negative

amount of energy released when gaseous elements form one mole of ionic lattice structure. bonds being formed is always exothermic

When a reaction is exothermic, and has less moles of gas on product side:

increase temperature, increase pressure; why is it dificult to predict how the amount of product changes at equillbrium (3)

1. forward reaction is exothermic, so if temperature is increased, equillibrium will shift to left / reactants side, decreasing yield of product

2. product side has less moles, so increasing pressure will shift equillibrium to right side, increasing yield of products

3. difficult to predict relative contributions with opposing factors

ideal gas equation and units

pV= nRT

pressure = pa

V = m3

n = moles

R = gas constant (8.314)

T = temp, kelvin

relationship between m3, dm3, and cm3

m3 =

1000000 cm3 (1×10⁶)

1000 m3 (1×10³)

A student reacts an excess of magnesium with 25.0 cm3 of 0.500 mol dm–3 hydrochloric acid, HCl . The student also reacts an excess of magnesium with 25.0 cm3 of 0.500 mol dm–3 ethanoic acid, CH3COOH.

Explain why these two reactions of magnesium produce the same volume of gas but at different rates. (3)

1. same moles of [H+] produced by the end

2. HCl is strong acid and fully dissociates, CH3COOH is a weak acid, and only partially dissociates

3. greater H+ concentration in HCl, so more frequent collisions, increasing reaction rate

A buffer solution is prepared by dissolving 3.39 g of potassium hydroxide in 250 cm3 of 0.376 mol dm–3 butanoic acid. This buffer solution has a pH of 5.07 at 25 °C.

Calculate the acid dissociation constant, Ka, of butanoic acid at 25 °C.

Assume that the volume of the solution remains constant at 250 cm3 when the potassium hydroxide is dissolved. (4)

1.5(3) x 10^–5

Colour of MnO4- and Mn2+

clear and pink

Describe the precipitation reaction of Copper and potassium iodide

2Cu²⁺ + 4I^- → 2CuI + I₂

_{Forms white precipitate of CuIm from blue solution}

An acidified solution containing Cr2O7 2– ions reacts with vanadium(III) ions in a redox reaction to form a solution containing Cr3+ ions and VO2 + ions. Construct the overall equation

2H+ + Cr₂O₇2- + 3V3+ → 2Cr3+ + H₂O + 3VO₂+

Explain Aluminium’s high melting point

Al: Giant metal lattice structure and metallic bonding. strong electrostatic attraction between positive metal ions and delocalised electrons. a lot of energy needed to break bonds

Explain Si’s very high melting point

Si: giant covalent structure, strong covalent bonds between atoms, between each pair of shared electrons and nuclei of atoms. each Si atom forms 4 bonds with other Si atoms.

Electron affinity definition

The enthalpy change when one mol of gaseous atoms / ions gains an electron to decrease their charge by 1

[Cr(NH3)6]3+ colour

purple solution

[Cr(OH)6]3- colour

dark green solution

Draw a graph of the melting points of Al to Ar

Al, then Si a lot higher

all lower than al:

S higher than P

Cl lower than P

Ar higher than Cl

Explain why silicone has a higher melting point than aluminium (3)

Aluminium has giant metallic structure and metallic bonding

Si has giant covalent structure and strong covalent bonds

More energy required to break covalent bonds in giant covalent structure than metallic bonds

Write what observations are seen when Br2 reacts with I-

No reaction or colour change, solution remains orange

Draw and explain molecular shape of H2S

KP=8,13

H2O (g) + Co(g) → H2(g) + CO2 (g)

Equal number of moles of steam and carbon monoxide at start

At equilibrium, H2 and CO2 both have partial pressure of 211kPa

Calculate partial pressures of H2O and CO at equilibrium

Both equal 74

Draw a Boltzmann distribution curve showing how platinum catalyser increases rate of reaction

if gradient is negative on Arrhenius equation, Ea is

Positive

Explain why buffer solution resists change in pH when a small amount of alkali is added, using general equations

OH- reacts with H+

HA → (reversible) H+ + A-

Equilibrium shifts right to oppose the change of H+ concentration decreasing

Minimising change in HA / A-

Explain the relative reactivites of Halo-alkane precipitates and ammonia

Ag-Cl: dissolves in dilute ammonia

Ag-Br: dissolves in high concentration ammonia

Ag-I: does not dissolve in ammonia