Chemistry Past Paper Corrections 2018

Question 1

What affects enthalpy change of hydration?

Answer 1

Size of molecules:
-Smaller molecules are more exothermic
-Greater attraction to H2O
Charge of molecules:
-Greater charges are more exothermic

Question 2

Average bond enthalpy

Answer 2

Enthalpy change when 1 mole of bonds are broken in gaseous molecules

Question 3

How does temperature affect Kp?

Answer 3

If the temperature increases in an exothermic reaction, Kp will decrease because the products (numerator) are decreasing

Question 4

How does Le Chatelier’s principal work in terms of pressure and Kp?

Answer 4

If pressure increases, the denominator increases (depends on side with more moles) because products are increasing
Therefore the numerator increases to RESTORE Kp
So the equilibrium shifts to the right

Question 5

Percentage dissociation

Answer 5

[H+]/[HA] x100

Question 6

What affects boiling points in molecules?

Answer 6

LONDON FORCES
In non polar molecules
As the number of electrons increases, boiling point increases
More energy is needed to break London forces

Question 7

Ideal gas equation

Answer 7

PV=nRT
P=pressure in pa
V=volume in m2
n=moles
R=8.314
T=temperature in kelvin

Question 8

What is the test for starch?

Answer 8

Iodine

Turns from yellow to blue/black

Question 9

Removing electrons

Answer 9

The leave the 4s subshell first!

Question 10

What are the conditions of standard electrode potentials?

Answer 10

25 degrees

1 mol/dm3 solutions

Question 11

When reacting half equations, what rule is used?

Answer 11

The anticlockwise rule

Question 12

In ligand substitution, how many bonds are formed and what affects it?

Answer 12

Usually 6, but 4 in chlorine

Question 13

What does the LOWEST atom economy mean?

Answer 13

The worst atom economy

Question 14

How does purity affect melting points?

Answer 14

Impure compounds have lower melting points

Question 15

Alcohol to haloalkane

Answer 15

NaCl and H2SO4

Forms product and NaHSO4 and H2O

Question 16

What is an easy trick they can play when oxidising alcohols?

Answer 16

Tertiary alcohols dont oxidise

Question 17

What is the number on [O] when oxidising to aldehydes/ketones?

Answer 17

1

Question 18

What is the number on [O] when oxidising to carboxylic acids?

Answer 18

2

Question 19

What happens when HCl acid is added to molecules such as amino acids?

Answer 19

NH2 becomes NH3+Cl- salt

COOH is not affected

Question 20

WHat happens when NaOH alkali is added to molecules such as amino acids

Answer 20

NH2 not affected
COOH becomes COO-Na+ salt
OH on phenols become O-NA+

Question 21

Why are phenols more reactive than benzene?

Answer 21

OH partially delocalises into the pi system
The electron density increases
The phenol is more susceptible to an electrophilic attack

Question 22

How does the halogen affect the rate of reaction?

Answer 22

Iodine is less reactive, so has a weaker bond, so the reaction is faster
Chlorine is more reactive, so has a stronger bond, so the reaction is slower

Question 23

What is the correct wording when talking about E/Z isomers

Answer 23

Priority groups

Largest atomic number

Question 24

Test for an aldehyde

Answer 24

Tollens’ reagent

Silver mirror

Question 25

Test for carbonyls

Answer 25

2,4-DNP Orange precipitate produced Can use the melting points of the precipitate to determine to compound by comparing them to predetermined values

Question 26

nitrile to amine

Answer 26

Reduction LiALH4 and H2SO4 Or H2 and Ni catalyst (this is the same as for alkene to alkane)

Question 27

WHat is easy to forget when reducing aldehydes

Answer 27

The carbon on the C=O is easy to miss when it becomes an alcohol

Question 28

Nitrile to a carboxylic acid

Answer 28

H2O, dilute HCL and reflux | Can sometimes be said to just be H+

Question 29

How are major and miner products determined in electrophilic addition?

Answer 29

Less reactive atom attaches to the carbon with the most hydrogens

Question 30

What happens when you add Na2CO3 to phenol?

Answer 30

COOH becomes COO-Na+ | OH is not affected

Question 31

What affects boiling points?

Answer 31

Non polar molecules- London forces | Polar molecules- hydrogen bonding

Question 32

WHat reacts with water to make an acid?

Answer 32

Chlorine or fluorine (HCl or HF)

Question 33

What can be tricky with density of molecules?

Answer 33

If the element makes X2, the density will be double

Question 34

What happens to electrical conductivity when an ionic lattice is a liquid?

Answer 34

IONS become mobile, not electrons! | The ions are free to carry a charge

Question 35

What is a reducing agent?

Answer 35

Something that is oxidised itself

Question 36

In standard electrode potentials, what is good to remember about the more positive half equation?

Answer 36

It is oxidised It is on the bottom in the anticlockwise rule It on the right hand side of the setup It is less reactive

Question 37

In standard electrode potentials, what is good to remember about the more negative half equation?

Answer 37

It is reduced It is on the top in the anticlockwise rule It is on the left hand side of the setup It is more reactive

Question 38

When writing transition metal equations, such as ligand substitutions, what is good to remember?

Answer 38

If you write HCl, dont forget the H+ on the other side | Or just write Cl-, then nothing is needed on the other side

Question 39

Nitrobenzene to phenylamine

Answer 39

Tin and concentrated HCl Reflux Neutralise with NaOH

Question 40

Purification steps

Answer 40

``` -Dissolve impure solid in MINIMUM volume of hot solvent Cool solution FIlter solid to remove impurities Recrystalisation Scratch with a glass rod Wash with a cold solvent and dry ```

Question 41

Enthalpy change of neutralisation

Answer 41

When 1 mole of water is formed from a neutralisation reaction Watch out when doing neutralisation calculations and there are 2 moles of water

Question 42

n(X)

Answer 42

Moles of X

Question 43

Esterified

Answer 43

Made into an ester

Question 44

Addition reaction

Answer 44

When two molecules become one