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A Level > Chemistry Past Paper Corrections 2018 > Flashcards

Chemistry Past Paper Corrections 2018 Flashcards

1
Q

What affects enthalpy change of hydration?

A 
Size of molecules:
-Smaller molecules are more exothermic
-Greater attraction to H2O
Charge of molecules:
-Greater charges are more exothermic
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2
Q

Average bond enthalpy

A

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

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3
Q

How does temperature affect Kp?

A

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

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4
Q

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

A

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

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5
Q

Percentage dissociation

A

[H+]/[HA] x100

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6
Q

What affects boiling points in molecules?

A

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

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7
Q

Ideal gas equation

A 
PV=nRT
P=pressure in pa
V=volume in m2
n=moles
R=8.314
T=temperature in kelvin
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8
Q

What is the test for starch?

A

Iodine

Turns from yellow to blue/black

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9
Q

Removing electrons

A

The leave the 4s subshell first!

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10
Q

What are the conditions of standard electrode potentials?

A

25 degrees

1 mol/dm3 solutions

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11
Q

When reacting half equations, what rule is used?

A

The anticlockwise rule

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12
Q

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

A

Usually 6, but 4 in chlorine

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13
Q

What does the LOWEST atom economy mean?

A

The worst atom economy

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14
Q

How does purity affect melting points?

A

Impure compounds have lower melting points

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15
Q

Alcohol to haloalkane

A

NaCl and H2SO4

Forms product and NaHSO4 and H2O

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16
Q

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

A

Tertiary alcohols dont oxidise

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17
Q

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

A

1

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18
Q

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

A

2

19
Q

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

A

NH2 becomes NH3+Cl- salt

COOH is not affected

20
Q

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

A

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

21
Q

Why are phenols more reactive than benzene?

A

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

22
Q

How does the halogen affect the rate of reaction?

A

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

23
Q

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

A

Priority groups

Largest atomic number

24
Q

Test for an aldehyde

A

Tollens’ reagent

Silver mirror

25
Q

Test for carbonyls

A

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

26
Q

nitrile to amine

A

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

27
Q

WHat is easy to forget when reducing aldehydes

A

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

28
Q

Nitrile to a carboxylic acid

A

H2O, dilute HCL and reflux

Can sometimes be said to just be H+

29
Q

How are major and miner products determined in electrophilic addition?

A

Less reactive atom attaches to the carbon with the most hydrogens

30
Q

What happens when you add Na2CO3 to phenol?

A

COOH becomes COO-Na+

OH is not affected

31
Q

What affects boiling points?

A

Non polar molecules- London forces

Polar molecules- hydrogen bonding

32
Q

WHat reacts with water to make an acid?

A

Chlorine or fluorine (HCl or HF)

33
Q

What can be tricky with density of molecules?

A

If the element makes X2, the density will be double

34
Q

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

A

IONS become mobile, not electrons!

The ions are free to carry a charge

35
Q

What is a reducing agent?

A

Something that is oxidised itself

36
Q

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

A

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

37
Q

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

A

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

38
Q

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

A

If you write HCl, dont forget the H+ on the other side

Or just write Cl-, then nothing is needed on the other side

39
Q

Nitrobenzene to phenylamine

A

Tin and concentrated HCl
Reflux
Neutralise with NaOH

40
Q

Purification steps

A 
-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
41
Q

Enthalpy change of neutralisation

A

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

42
Q

n(X)

A

Moles of X

43
Q

Esterified

A

Made into an ester

44
Q

Addition reaction

A

When two molecules become one

A Level (25 decks)

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