Questions

Question 1

Suggest an analytical technique that could be used to determine the presence of copper ions

Answer 1

Emission/absorption spectra

Question 2

Using your knowledge on chemistry, suggest why animals have different coloured blood

Answer 2

Relating to split d orbitals: electrons in the lower energy d orbitals can absorb energy and move to higher energy d orbitals. If the energy absorbed in these d-d transitions is in the visible part of the electromagnetic spectrum the colour of the transition metal compound will be complementary to the colour absorbed. So the colour we see will be white light minus the colour absorbed.

Question 3

State what is meant by “weigh accurately approximately”

Answer 3

That the exact mass should be measured accurately and should be close to the given measure.

Question 4

Suggest an improvement a student could make to reduce uncertainty in a titre value

Answer 4

Use lower concentration of solution.

Question 5

Explain why volumetric method is more appropriate to use than the gravimetric method

Answer 5

Volumetric method is more accurate and uses smaller quantities

Question 6

Describe how pi bonds are formed

Answer 6

Pi bonds arise when atoms form multiple bonds and the orbital overlap side-on.

Question 7

State two factors that should be considered when selecting an appropriate solvent for recrystallisation.

Answer 7

Doesn’t react with solute and it’s polarity

Question 8

Pauli exclusion principle?

Answer 8

The Pauli exclusion principle states, that no two electrons in the same atoms should have the same four quantum numbers

Question 9

Aufbau principle?

Answer 9

The Aufbau principle states, that electrons fill orbitals in order of increasing energy. Meaning the lowest sub-shells are filled first.

Question 10

Hunds rule?

Answer 10

Hinds rule states that when degenerate orbitals are available, electrons fill each deferral orbital singly and with parallel spins, before pairing up to fill the orbitals.

Question 11

I’m gravimetric analysis, why is a desiccator used?

Answer 11

To prevent the reabsorption of water

Question 12

Back titration?

Answer 12

A back titration also known as an indirect titration allows the concentration of an unknown solution to be determined by reacting it with a known excess of a reagent

Question 13

What is a standard solution?

Answer 13

A standard solution is a solution of accurately known concentration

Question 14

What characteristics must a primary standard have?

Answer 14

• Be available in a high state of purity
• Be stable when solid and in solution
• Be soluble in water and have a relatively high GFM to reduce the percentage errors when weighing

Question 15

What is gravimetric analysis used for?

Answer 15

To determine the mass of an element or compound in a substance

Question 16

How are molecular orbitals formed?

Answer 16

They are formed when we bring together two atoms to form a bond, then the two orbitals then combine to form molecular orbitals

Question 17

What is the section of a conjugated system that allows colour to be seen?

Answer 17

The chromophore

Question 18

The larger the conjugated system..

Answer 18

The smaller the gap between HOMO & LUMO

Question 19

What does a longer conjugated system mean?

Answer 19

That the gap between HOMO & LUMO is smaller

Question 20

What does a smaller conjugated system mean?

Answer 20

That the gap between HOMO & LUMO is larger

Question 21

What is colorimetry used for?

Answer 21

Is is used to determine the concentration of coloured substances in a solution

Question 22

What is a calibration graph used for?

Answer 22

To determine the concentration of the test sample

Question 23

Using your knowledge of chemistry, discuss factors which should be considered when selecting appropriate chemical for a titration

Answer 23

• a standard solution is a solution of accurately known concentration
• a standard solution can be prepared from a primary standard, which involves weighing out the primary standard accurately and dissolving it in deionised or distilled water in a beaker
• the solution plus all the rinsings are transferred into a standard flask made up to the mark/line with more deionised water.
• a primary standard must have the following characteristic: be available in a high state of purity; be stable when solid and when in solution; be soluble in water and have a reasonably high GFM to reduce the percentage errors when weighing

Question 24

Heterogeneous catalysts?

Answer 24

Heterogeneous catalysts are in a different physical state to the reactant in the reactions being catalysed

Question 25

State how transition metals can act as catalysts

Answer 25

d electrons/ unpaired

Unfilled d-orbitals or electrons can be donated or accepted due to variable oxidation states

Question 26

Explain how a line is produced on an emission spectrum.

Answer 26

Electrons can either be promoted where they move to a lower energy level and emit a photon of light or they can either be excited, gain energy and move to a higher energy level

Question 27

Explain why there is a series of lines at discrete wavelengths in the emission spectrum of cadmium?

Answer 27

Each different transition will correspond to a different wavelength of light

Question 28

In an experiment to determine the equilibrium constant, k, 0.0100 mol of PCl5 was placed in a sealed 1.00 litre flask and heated to 250degrees Celsius. At equilibrium 0.0420 mol of PCl3 had been formed.

Calculate the equilibrium constant, k, for the reaction at 250degrees Celsius.

Answer 28

no. of mol PCl5 unreacted = 0.01000 - 0.0420= 0.058

k= [PCl3] [Cl2]/ [PCl5] = [0.0420] [0.0420]/ [0.058] = 0.0304.

Question 29

The temperature of the equilibrium mixture was increased to 400degrees Celsius.

Explain the effect of this change in temperature on the value of the equilibrium constant, k.

Answer 29

Increase in temperature favours the endothermic reaction (forward reaction), so more products formed and less reactants remain.

k= increase in [product concentration]/ decrease in [reactant concentration] = value of k increases

Question 30

Phosphorus oxychloride, POCl3, has a similar three-dimensional structure to the [PCl4]^+ ion.

Suggest a reason why the bond angle in the POCl3 molecule is less than the bond angle in the [PCl4]^+ ion.

Answer 30

Greater electron repulsion from P=O

Question 31

What is meant by a dative covalent bond?

Answer 31

Both electrons in the bond come from the same atom.

Question 32

Using you knowledge of chemistry, discuss the strengths and weaknesses of a simple model of an atom compared to the concepts of atomic structure and binding at advanced higher level

Answer 32

Electrons within atoms have a fixed amount of energy called quanta. It is possible to describe any electron using the four quantum numbers; the principle quantum number; the angular momentum; the magnetic; and the spin magnetic quantum number. Electrons within atoms are arranged according to the 3 rules; the aufbau principle; hunds rule and Pauli exclusion principle. (Go onto explain the rules)

Question 33

The concentration of hydrogen peroxide determined by the student was less than the concentration stated on the label for the stain remover.

One possible source of error could be and inaccurate concentration of the permanganate solution.

Describe how the student would confirm the concentration of the permanganate solution.

Answer 33

Carry out colorimetry with a solution of accurately known concentration

Question 34

Using your knowledge of chemistry, suggest how the chemicals in a stain remover might work on these stains?

Answer 34

Most organic molecules appear colourless because the energy gap between the HOMO & LUMO Is relatively large. This results in the absorption of light from the ultra violet region of the spectrum and so no visible light is absorbed.

Some organic molecules contain chromophores which is a group of atoms within a molecule that is responsible for the absorption and the detection of light from the visible region of the spectrum. Light can be absorbed when electrons in a chromophore are promoted from the HOMO to LUMO.

Question 35

Suggest why mixtures are heated under reflux?

Answer 35

To prevent vapours from escaping

Question 36

Explain fully why a dye molecule will absorb a shorter wavelength of light than the other molecules.

Answer 36

Smaller conjugation or smaller chromophore

Question 37

Explain fully how colour arises in dye molecules.

Answer 37

Electrons move from HOMO to LUMO and if the absorption of light is from the visible part of the spectrum light of the complementary is seen

Question 38

The absorbance of the same solution was 0.71. The sample solution was then diluted to decrease the concentration by half.

The absorbance of this diluted solution was then measured.

Explain why the sample solution was diluted.

Answer 38

Unknowns absorbance must not be out with the calibration graph

Question 39

State the brønsted-lowry definition for a base

Answer 39

Proton or H+ acceptor

Question 40

State the brønsted-lowry definition for an acid

Answer 40

Proton or H+ donator

Question 41

Using your knowledge of chemistry, discuss the role of acids and based in pH Indicators and buffer solutions

Answer 41

Indicators are used in acid base titrations as they change the colour of the end point if the reaction. Inductors are usually weak acids in which the colour of the acids is different to that of its conjugate base. Adding acids will shift equilibrium to the left hand side. Adding alkali will remove H+ ions from equilibrium and the position will move to right side. For a substance to be a useful indicator the colour of the non ionised form must be distinctly different from the conjugate base

A buffer solution is one in which the pH remains approximately constant when small amounts of acid, base or water is added. When acid is added to buffer solutions the added H+ ions from the acid react with ions from the salt forming more undissociated acid molecules.
When alkali is added OH- ions from the alkali react with hydrogen ions from the acid. pH remains unchanged. A basic buffer solution consists of a weak base and one if it’s salts. The weak base removes any added hydrogen ions. The conjugate acid replaces any hydrogen ions removed when alkali was added

Question 42

[Zn(H2O)6]2+

Name this complex ion

Answer 42

Hexaaquazinc(II)

Question 43

Electron transitions involving d-sub-shells can give rise to colour in transition metal complexes

Explain y why a solution of the complex ion is colourless

Answer 43

There are no d-d traction’s possible so no visible light is absorbed