Chemistry pre-2017 paper corrections

Question 1

What are polyamides used for?

Answer 1

Making fabrics like nylon

Question 2

What is the attraction in chromatography called?

Answer 2

Adsorbtion

Question 3

What is the isoelectric point?

Answer 3

The pH that an amino acid exists as a zwitterion

Question 4

What is the difference between producing an amino acid in a lab or using bacteria?

Answer 4

In the lab two optical isomers are formed/racemic mixture

Bacteria only form one product

Question 5

In mass spectrometry, what must all the species be?

Answer 5

Positive in order to show up on the spectrum

Question 6

What are the products of hydrolysis of the amide bond with HCl?

Answer 6

a carboxylic acid COOH and NH3+

Question 7

How many [H] are there in reduction of aldehydes to alcohols?

Answer 7

2[H]

Question 8

How can melting points of ionic compounds be determined?

Answer 8

By the size of their radius

This is due to their ELECTRON/CHARGE DENSITY so you have to add up the sum of the radii of the two ions

Question 9

When talking about when Gibbs Free Energy is feasible, what is good to write?

Answer 9

When talking about when /\G is negative, talk about not just T/\S but when /\H - T/\S > 0

Question 10

What do you need to remember when calculating Kc?

Answer 10

To use concentration, not moles

Question 11

Why might a reaction be unlikely to take place in just one step?

Answer 11

Because the stoichiometry in the rate equation doesn’t match the overall equation
Because a collision is unlikely to occur with more than 2 ions

Question 12

Why is scandium not a transition metal?

Answer 12

Its ion doesn’t have and incomplete d subshells

All its d orbitals are empty

Question 13

Why is zinc not a transition metal?

Answer 13

Its ion doesn’t have and incomplete d subshells

All its d orbitals are full

Question 14

When drawing transition metal ions what is easy to forget but often isn’t needed anyway?

Answer 14

The brackets and charge on the ion

Question 15

How does ligand substitution allow haemoglobin to transport oxygen in the blood?

Answer 15

O2 bonds reversibly to the Fe2+ ion

O2 can be released

Question 16

What do you need to mention when explaining why a buffer solution has formed?

Answer 16

The actual names of the acid and the salt eg. CH3CHOOH and CH3COO-

Question 17

What is the definition of standard electrode potential?

Answer 17

The e.m.f of a half cell compared to the standard hydrogen electrode

Question 18

What are the standard conditions of the standard electrode potential?

Answer 18

25 degrees, 1 moldm-3 and 1 atm

Question 19

Why does the cell potential increase when water is added to a Cu2+/Cu half cell?

Answer 19

• Because the concentration of Cu2+ decreases because it reacts with the water
• This makes the equilibrium shift to the left to replace the lost ions
• This means more electrons are released by Cu
• So the cell has a bigger difference in E

Question 20

What do you need to include when talking about which is the reducing agent?

Answer 20

That the reducing agent loses electrons because it is oxidised
Also which species it loses the electrons to

Question 21

When there is a transition metal ion present and it forms a precipitate, what is likely to be the solid compound?

Answer 21

Ending in (OH)
eg. Fe(OH)3

Question 22

What is a molecular formula?

Answer 22

Just the simplest formula of number of atoms

eg. C2H6O

Question 23

In precipitation reactions, how do you know how many ligands to add?

Answer 23

You add them until the oxidation number is 0
For most of them this will be 2 as they are 2+ ions
But it might be 3 if it is a 3+ ion

Question 24

In ligand substitution, how do you know how many ligands to swap?

Answer 24

For some it will be a full substitution, but for some like copper and excess NH3, it is only partial substitution and will make [Cu(NH3)4(H2O)2]2+. This is redissolving

Question 25

When is there an NH3 ligand?

Answer 25

Only when it is in excess and there is ligands substitution

Otherwise it is OH- ligand because it takes an H+ off of H2O

Question 26

How can you tell from half lives on the graph show a 1st order reaction?

Answer 26

If the half lives are CONSTANT

Question 27

Why is a two/three step mechanism consistent with the rate equation?

Answer 27

Because, for example, steps 1 and 2 together give species in the same ratio as in the rate equation

Question 28

When working out buffers from a change in solution, what can affect the amount you add and subtract from [HA] and [A-]?

Answer 28

The charge on the element added
For example, if Mg is added, then the charge is 2+ so will double the amount of salt being increased and acid being decreased

Question 29

In the Born - Haber cycle, what are the species on the level 2nd up from the ionic compound?

Answer 29

The elements in their standard state, so is will be I2 and not 2I

Question 30

What should you always look out for whenever electron configuration comes up? (especially when they are ions)

Answer 30

THE ELECTRONS COME OUT OF THE 4S SUBSHELL FIRST!!!!

Question 31

What is the pH at the hydrogen electrode?

Answer 31

0

Question 32

Why does the pH of the solution in the hydrogen half cell decrease as this cell delivers current?

Answer 32

Because the redox system is more negative so releases electrons
So the equilibrium shifts to increase [H+]

Question 33

What is the difference between a fuel cell and a modern storage cell?

Answer 33

Fuel reacts with oxygen to give electrical energy

Question 34

What is the reaction of Na2O with H2O?

Answer 34

Makes NaOH

Question 35

What is the reaction of NaFeO2 and H2O?

Answer 35

Fe(OH)3 and NaOH is produced