Past Exam Papers Flashcards
Define the term enthalpy of lattice formation. [2 marks]
The enthalpy change when one mole of a solid ionic compound/lattice is formed from its gaseous ions.
A calculation of the enthalpy change of lattice formation of silver iodide based on a perfect ionic model gives a smaller numerical value than the value calculated in Question 1.2.
Explain this difference. [2 marks]
- AgI contains covalent character/ is not completely ionic
-so the forces/bonds holding the lattice together are stronger
Identify a reagent that could be used to indicate the presence of iodide ions in an aqueous solution and describe the observation made. [2 marks]
-AgNO3
-A yellow coloured precipitate is formed
What is the correct expression for Kw? [1 mark]
C - Kw= [H+][OH-]
Calculate the pH of pure water at 10ºC. Give your answer to 2 decimal places. [2 marks]
[H+] = √Kw = √2.93*10^-15
[H+] = 5.41 X 10^-8
pH = -log(ans) = 7.27
pH = 7.27
Suggest why this pure water at 10ºC is not alkaline.
[H+] = [OH-]
Calculate the pH of a 0.0131moldm-3 solution of calcium hydroxide at 10ºC. Give your answer to two decimal places. [3 marks]
[OH-] = 0.0131 X 2 = 0.0262
[H+] = (2.93X10^-15)/0.0262 = 1.118X10^-13
pH = -log(ans) = 12.95
pH = 12.95
Predict whether the pH of magnesium hydroxide solution formed at 10ºC is larger than, smaller than or the same as the pH of calcium hydroxide solution at 10ºC.
Explain your answer. [2 marks]
-smaller pH
-magnesium hydroxide is less soluble than calcium hydroxide
Write an equation, including state symbols, to show how an atom of titanium is ionised by electron impact and give the m/z value of the ion that would reach the detector first. [2 marks]
Ti(g) -> Ti+(g) + e-
m/z value = 46
46 - 9.1
47 - 7.8
48 - 74.6
49 - 8.5
Calculate the relative atomic mass of titanium in this sample. Give your answer to one decimal place. [2 marks]
Ar = (46 X 9.1) + (47 X 7.8) + (48 X 74.6) + (49 X 8.5)
Ar = 4782.5/100 = 47.8
Ar = 47.8
Calculate the mass, in kg, of one atom of 49Ti. [1 mark]
49/(6.022 X 10-23)
= (8.136 X 10-23)/ 1000
Mass = 8.14 X 10-26 kg
Ke of an ion in the flight tube = 1.01310-13 J
Time of flight of a 49Ti+ ion = 9.81610-7s
Calculate the time of flight of a 47Ti+ ion. Give your answer to the appropriate number of significant figures. [3 marks]
d = t√2E/m
d = (9.816 X 10^-7) √2(1.013 X 10^-13)/(8.14 X 10^-26)
d = 1.55m
t = (1.5468) √(7.504716 X 10^-26)/ 2(1.013 X 10^-13)
t = 9.61 X 10^-7s
20.1mol CO and 24.2 mol H2 placed in sealed container. Equilibrium mixture contained 2.16mol methanol.
Calculate the amount, in moles, of carbon monoxide and of hydrogen in the equilibrium mixture. [2 marks]
Start: 20.1, 24.2 , 0
/2.16 (reactants) *2.16 (products)
End: 17.94 , 19.88 , 2.16
Amount of CO = 17.9 mol
Amount of H2 = 19.9 mol
Deduce the oxidation states of Nitrogen in NO3- and NO. [2 marks]
NO3- : +5
NO : +2
Name the mechanism for Reaction 2 and give an essential condition to ensure that CH3CH2CH2HN2 is the major product. [2 marks]
Nucleophilic substitution and excess NH3
Give the IUPAC name of CH3CH2CH2CH2CH(OH)CN. [1 mark]
1-hydroxyhexanenitrile
Describe how you would distinguish between separate samples of the two stereoisomers of CH3CH2CH2CH2CH(OH)CN. [2 marks]
- plane of polarised light
- each stereoisomer would rotate the light in opposite directions
Explain why the reaction produces a racemic mixture. [3 marks]
- planar carbonyl group
-can be attacked from either side - with equal probability
Describe how you would distinguish between all four compounds using the minimum number of tests on each compound. [6 marks]
-COOH
- sodium carbonate, effervescence, cloudy limewater
- K and M but not L or N
-OH and -CHO
- acidified potassium dichromate, solution would turn green from yellow
- K, L or N but not M
-CHO
- Fehling’s solution , will go brick red from blue
- N only
-Br
- silver nitrate, cream precipitate formed
- L or N
State in general terms what determines the distance travelled by a spot in TLC. [1 mark]
It’s solubility
To obtain the chromatogram, the TLC plate was held by the edges and placed in the solvent in the beaker in the fume cupboard. The lid was then replaced in to the beaker. [1 mark]
Ensure the solvent doesn’t touch the pencil line
Deduce the relative polarities of 1,2-dinitrobenzene and 1,4-dinitrobenzene and explain why 1,4-dinitrobenzene has the greater Rf value. [2 marks]
Relative polarities: 1,2 is more polar
Explanation: less polar so more attracted to solvent (less soluble) so travels further
State two features of the current model that are not shown in the Rutherford model. [2 marks]
- Protons and Neutrons in the nucleus
- There are multiple energy levels that contain electrons
Describe the bonding in magnesium. [2 marks]
- metallic bonding is present
- attraction between the lattice of positive metal ions and sea of delocalised electrons
Explain, in terms of structure and bonding, why magnesium chloride has a high melting point. [3 marks]
- MgCl2 is a giant ionic lattice
- there are strong electrostatic forces of attraction
- between the oppositely charged Mg2+ and Cl- ions
Give one medical use for magnesium hydroxide. [1 mark]
Indigestion relief
State, in terms of electrons, the meaning of the term oxidising agent. [1 mark]
An electron acceptor
Chlorine has a low boiling point because the forces between the molecules are weak.
Explain how these forces arise between molecules of chlorine. [3 marks]
- there is movement of electrons in one of the molecules
- which induces a dipole in the neighbouring molecule
- and the temporary dipoles created attract
State the meaning of the standard enthalpy of combustion. [2 marks]
The enthalpy change when one mole of a substance is completely burnt in oxygen with all substances in their standard states.
Explain why there is an attraction between a C=C double bond and Br2. [3 marks]
- Br2 contains an induced dipole and the slight charges causes the molecule to become polarised
- the slight positive charge on one of the Br molecules is attracted to the C=C double bond
- due to the area of high electron density around the double bond
Explain why propanone has a lower boiling point than propan-2-ol. [3 marks]
- Propan-2-ol has hydrogen bonding
- Therefore has stronger IM forces compared to the weaker VDW forces of the propanone
- so needs less energy to overcome the bonds in propanone
State the benefit to life on earth of ozone in the upper atmosphere. [1 mark]
It absorbs UV, which is harmful
Suggest one reason why the use of CFCs was not restricted until several years after Rowland and Molina published their research. [1 mark]
There was an initial lack of evidence to support their research
CFC-11 is a greenhouse gas that can contribute to global warming.
State and explain how CFC-11 is able to contribute to global warming. [2 marks]
- the bonds in CFC-11 are able to absorb IF radiation
- due to their polarity
- so the IF radiation gets trapped in the atmosphere
Define the term enthalpy change. [1 mark]
The heat energy change at a constant pressure
