PAPER 1 worded questions

Question 1

Suggest what might cause the relative atomic mass of this sample to be
different from the relative atomic mass given in the Periodic Table

(1 mark)

Answer 1

Other isotopes present / some isotopes absent / different abundances of
isotopes

Btw isotopes is UNDERLINED

Question 2

State the m / z value of the ions that produce the biggest current at the detector
when the spectrum in the graph is recorded.
Give a reason for your answer. (2 marks)

Answer 2

Mark 1: say the one with the biggest line on the graph

Mark 2: highest realative abundence

Question 3

The mass spectrum of tellurium also has a small peak at m / z = 64
Explain the existence of this peak. (2 marks)

Answer 3

Mark 1: 2+ ion formed / 2 electrons removed
Mark 2: due to terleium 128

Due to 128Te2+ = 2 marks

Question 4

Predict whether the atomic radius of 124Te is larger than, smaller than or the same as
the atomic radius of 130Te
Explain your answer. (2 marks)

Answer 4

Mark 1: the same
Mark 2:
(Each isotope has the) same number of protons / same nuclear charge and
same number of electrons / electronic configuration

Question 5

Describe how ions are formed in a time of flight (TOF) mass spectrometer. (2 marks)

Answer 5

Electrospray
Mark 1: A high voltage is applied to a sample in a polar solvent
Mark 2: the sample molecule, M, gains a proton forming MH+

or electron impact
Mark 1: the sample is bombarded by high energy electrons
Mark 2: the sample molecule loses an electron forming M+

Question 6

A TOF mass spectrometer can be used to determine the relative molecular mass of molecular substances.

Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer. (2 marks)

Answer 6

1) ions, not molecules, will interact with and be accelerated by an electric field
2) Only ions will create a current when hitting the detector

Question 7

In a mass spectrometer, the isotopes of an element are separated.
Two measurements for each isotope are recorded on the mass spectrum.

State the two measurements that are recorded for each isotope. (2 marks)

Answer 7

1) M/Z

2) relative abundence

Question 8

Define the term relative atomic mass

Answer 8

Average / mean mass of 1 atom (of an element)

1/12 mass of one atom of 12C

Question 9

In a mass spectrometer, the relative abundance of each isotope is proportional to the current generated by that isotope at the detector.

Explain how this current is generated. 2 marks

Answer 9

Electron(s) transferred / flow (at the detector)
M1 must refer to electron flow at the detector.

M2 : (From detector / plate) to the (+) ion

Question 10

Outline how the TOF mass spectrometer is able to separate these two species to give two peaks. ( 4 marks)

Answer 10

1. Positive ions are accelerated by an electric field
2. To a constant kinetic energy
3. The positive ions with m / z of 104 have the same kinetic energy as those with m / z of 118 and move faster
4. Therefore, ions with m / z of 104 arrive at the detector first

Question 11

Explain the meaning of the term first ionisation of an atom.

2 marks

Answer 11

Enthalpy change is required to remove 1 mole of electrons from 1 mole of a gaseous ions

Question 12

Explain what is meant by the term electronegativity

Answer 12

ability (or power) of an atom to attract electron density
(or electrons or ‑ ve charge) (1)
in a covalent bond (1)

Question 13

Suggest how a student doing this experiment could check that all the water had been removed

Answer 13

Reheat it

and check if the mass is constant

Question 14

Describe the structure of and bonding in graphite and explain why the melting point of graphite is very high

Answer 14

Layers of (C atoms)
Connected by covalent bonds within each layer
Van der Waals forces/IMF between layers/weak forces between layers
Many/strong covalent bonds need to be broken

Question 15

Suggest one property of an impurity that would cause the calculated mass of FeSO4.7H2O in X to be greater than the actual mass of X.

Explain your answer

Answer 15

Impurity is a) reducing agent / reacts with dichromate / impurity is a version of
1
1
FeSO
4
with fewer than 7 waters (not fully hydrated)
Allow a reducing agent or compound that that converts Fe3+ into Fe2+
Such that for a given mass, the impurity would react with more dichromate
than a similar mass of FeSO4.7H20
OR for equal masses of the impurity and FeSO4.7H2O , the impurity would react with more dichromate.
Must compare mass of impurity with mass of FeSO4.7H2O

Question 16

Explain why the value of Kw increases as the temperature increases. (2)

Answer 16

Dissociation OR breaking bonds) is endothermic M1

∴ Equilibrium moves to RHS (at higher T) to absorb heat or to lower T or oppose increase in T M2

Question 17

Suggest a suitable piece of apparatus that could be used to measure out the sodium hydroxide solution.

Explain why this apparatus is more suitable than a pipette for this purpose.

Answer 17

Burette

Because it can deliver variable volumes

Question 18

Two solutions on with a pH of 4 and one with a pH of 9 were left in the air

The pH of the pH 9.00 solution changed more than that of the other solution.

Suggest what substance might be present in the air to cause the pH to change.

Explain how and why the pH of the pH 9.00 solution changes.

Answer 18

M1- CO2
M2- pH (It) falls / decreases
M3- acidic (gas)
OR reacts with alkali(ne solution) / OH− OR CO2 + 2OH− CO32− + H2O
OR CO2 + OH−   HCO3−

Question 19

Explain why the expression for Kw does not include the concentration of water. (3)

Answer 19

H2O] is very high (compared with [H+] and [OH−]) OR
Very few H+ and OH− ions
OR
Only / very slightly dissociates
OR
Equilibrium lies far to the left

Question 20

State what is meant by the term buffer solution.

Identify a reagent which could be added to a solution of ammonia in order to form a buffer solution (3)

Answer 20

Buffer solution: A solution which resists change in pH (1)

when small amounts of acid or base added or on dilution (1)

Reagent: NH4Cl (1)

Question 21

State what is meant by the term Brønsted–Lowry acid.

Answer 21

A proton donor

Question 22

Define Kw

Answer 22

Kw =[H+][OH-]

Question 23

Define pH

Answer 23

-log([H+])

Question 24

Hydrogen carbonate ions (HCO3−) act as a weak acid in aqueous solution. Write an equation for this equilibrium.

Answer 24

HCO3- _> H+ + Co3-

Question 25

explain how a solution containing sodium hydrogencarbonate and sodium carbonate can act as a buffer when small amounts of acid or small amounts of alkali are added.

Answer 25

Acid: Increase in concentration of H+ ions, equilibrium moves to the left.

Alkali: OH- reacts with H+ ions, equilibrium moves to the right (to replace the H+ ions

Conc of H+ remains constant

Question 26

Suggest why chloroethanoic acid is a stronger acid than ethanoic acid.

Answer 26

M1- Cl is (more electronegative so) withdraws electrons OR negative inductive effect of Cl

M2- Weakens O–H bond
OR O–H bond is more polar
OR reduces negative charge on COO− OR stabilizes COO− (more)

Question 27

The dissociation of methanoic acid in aqueous solution is endothermic.

Deduce whether the pH of a solution of methanoic acid will increase, decrease or stay the same if the solution is heated.

Explain your answer.

Answer 27

Decrease

Equilibrium shifts to the right, or more H+ or Ka increases

M3. To reduce temp or oppose temp change

Question 28

Write an expression for pKa

Answer 28

-logKa

Question 29

State why calibrating a pH meter just before it is used improves the accuracy of the pH measurement.

Answer 29

Over time / after storage meter does not give accurate readings

Question 30

Describe how you would obtain the pH curve for the titration.

Answer 30

Any five from:
Ignore references to the use of the pipette, the filling of the
burette and the calibration of the pH meter.
• Measure pH (of the acid)
• Add alkali in known small portions
Allow 1 – 2cm3.
• Stir mixture
• Measure pH (after each addition)
• Repeat until alkali in excess
Allow 27 – 50cm3.
• Add in smaller increments near endpoint
Allow 0.1 – 0.5cm3.

Must follow a logical order

Question 31

The reaction between ammonia and oxygen was carried out at a higher temperature

Explain how this change affect the value of delta G, for the reaction

Answer 31

ΔG becomes more negative/less positive

The entropy change / ΔS is positive / TΔS gets bigger / -TΔS gets more negative.

Question 32

Suggest why it is important that the container for each sample has the same dimensions. (1)

Answer 32

Absorption depends on (proportional to) path length / distance travelled
through solution

Question 33

Suggest why the coloured filter is used. in calorimetry

Answer 33

To select the colour / frequency / wavelength that is (most strongly)
absorbed (by the sample)

Allow the filter is chosen to complement the colour of the
solution

Question 34

Suggest one reason why a colourimetric method might be chosen in preference to titration.

Answer 34

Quicker to analyse extracted samples than by titration /

uses smaller volumes of solution

Question 35

Give the equation that relates the energy change ΔE to the Planck constant h and the frequency of the visible light v.

Answer 35

ΔE = hv

Question 36

Explain why this electron transition causes a solution containing the transition metal ion to be coloured. (2)

Answer 36

M1: (One colour of) light is absorbed (to excite the electron)
M2:The remaining colour / frequency / wavelength / energy is transmitted (through the solution)

Question 37

The energy change shown in the diagram represents the energy of red light and leads to a solution that appears blue. Blue light has a higher frequency than red light.

Suggest whether the energy change ΔE will be bigger, smaller or the same for a transition metal ion that forms a red solution.

Explain your answer.

Answer 37

M1: Bigger
M2: Blue light would be absorbed
OR light that has greater energy than red light would be absorbed
OR higher frequency (of light absorbed / blue light) leads to higher ΔE

Question 38

State three different features of transition metal complexes that cause a change in the value of ΔE, the energy change between the ground state and the excited state of the d electrons.

Answer 38

Any three from:
• (Identity of the) metal
• Charge (on the metal) / oxidation state / charge on complex
• (Identity of the) ligands
• Co-ordination number / number of ligands
• Shape

Question 39

Suggest why the enthalpy change for the reaction in part (c) is approximately zero.

/(reaction in part c is n the complex ion [Cu(NH3)4(H2O)2]
2+ reacts with 1,2-diaminoethane, the
ammonia molecules but not the water molecules are replaced. )

Answer 39

M1: Cu–N bonds formed have similar enthalpy / energy to Cu–N bonds broken

M2: And the same number of bonds broken and made

Question 40

Explain why the reaction in part (c) occurs despite having an enthalpy change that is approximately zero.

Answer 40

3 particles form 5 particles / disorder increases because more particles are
formed / entropy change is positive (1)

Therefore, the free-energy change is negative (1)

M2 can only be awarded if M1 is correct

Question 41

Suggest why ions from s block elements do not usually act as catalysts

Answer 41

Only have 1 oxidation state

Question 42

Explain why Fe3+ ions are as effective as Fe2+ ions in catalysing this reaction.

Answer 42

Equations 1 and 2 can occur in any order

allow idea of Fe3+ converted to Fe2+ then Fe2+ converted back
to Fe3+