AS 2017 paper 2 - depth in chemistry Flashcards
What is meant by ionic bond ?
Electrostatic attraction between positive and negative ions
Calculate the no. of barium ions in 1.50g of barium oxide. Give your answer in standard form and to 3 sf.
n(BaO) =1.50/153.3 OR 9.78 x 10–3
(9.78 x 10–3
x 6.02 x 1023) = 5.89 x 10 21
Barium chloride, BaCl2, is soluble in water. Compare the electrical conductivities of solid and aqueous barium chloride. Explain your answer in terms of the particles involved
Barium chloride does not conduct electricity when solid because it has ions which are fixed (in position/in lattice. Barium chloride conducts when in aqueous solution because it has mobile ions.
Describe the use of aqueous barium chloride in qualitative analysis. (2)
Test for sulfate/SO42–
White precipitate forms (when barium chloride solution is
mixed with a solution containing sulfate ions)
Hydrated barium chloride can be crystallised from solution. Has the formula BaCl.H2O and a molar mass of 244.3g mol. Determine the value of x in the formula of BaCl2.H2O. (2)
M(BaCl2) = ((137.3 + (35.5 X 2)) = 208.3 (g mol–1)
244.3 – 208.3 = 36
36/18 = 2
Complete the electron configuration of a nitride ion.
1s2 2s2 2p6
Solid barium nitride is reacted with water, forming an alkaline solution A and an alkaline gas B. Identify A and B. Write an equation, include state symbols, for the reaction. (4)
products of reaction A = Barium hydroxide/Ba(OH)2 B = Ammonia/NH3 Formula for Barium nitride - Ba3N2 Balanced equation with state symbols Ba3N2(s) + 6H2O(l) ---3Ba(OH)2(aq) + 2NH3(g
A student was asked to carry out an experiment to determine the initial rate of reaction of zinc and hydrochloric acid. The student plans to collect a total of about 72cm of hydrogen at RTP and to use an excess of zinc.
The student selects the following apparatus -
- the apparatus shown in the diagram
100 cm measuring cylinder
2 dp balance
Outline how the student could carry out the experiment and explain how the results could be processed graphically. Show all working in your calculations (6)
- Method
- measure mass of (excess) zinc (using 2 decimal place balance)
- measure volume of hydrochloric acid
(using measuring cylinder)
- mix zinc and acid in flask
- measure gas volume at time intervals - Calculations
- moles of hydrogen
72/24000 = 0.00300 mol
- minimum mass of zinc
0.003 x 65.4 = 0.20 g
- moles of hydrochloric acid
Zn + 2HCl – ZnCl2 + H2
0.00300 x 2 = 0.00600 mol
- volume/concentration of acid
If [HCl(aq)] = 0.1 mol dm–3
appropriate
volume of acid = 0.006 x 1000/0.1 = 60 cm3
If [HCl(aq)] ≥ 0.3 mol dm–3
, too low (≤ 20 cm3)
If [HCl(aq)] ≤ 0.03 mol dm–3
too high (≥ 200 cm3) - Processing results
- Plot a graph of volume against time
- Draw a tangent at t = 0
- Gradient of tangent = initial rate
- Gradient = volume/time
A student carries out an experiment to measure the enthalpy change of combustion of hexane. The student finds out that combustion of 1.29g of hexane changes the temperature of 200g of water from 20.5 to 65.5 C.
- Calculate the enthalpy change of combustion of hexane in KJ.
Give your answer to an appropriate no. of sf.(4)
1.29/86.0
n(C6H14) = 0.0150 mol y = 37620 (J) OR 37.620 (kJ)
37.6/0.015 = 2507
∆H = –2510 (kJ mol–1)
The calculated value of /\ H for hexane from this experiment is different from the data book value. Suggest 2 reasons for this difference. (2)
- Heat released to the surroundings
- Incomplete combustion
- Non-standard conditions
Complete combustion of cyclohexane is shown below.
C6H12(l) + 9O2 (g) – 6CO2(g) + 6H2O(l).
Calculate the standard enthalpy change of combustion of cyclohexane (3)
6 × (–)393.5 AND 6 × (–)285.8 OR (–)2361 AND (–)1714.8 OR (–)4075.8 (6 × –393.5) + (6 × –285.8) – (–156.3) = – 3919.5 (kJ mol–1)
Describe the oxidation reactions of butan-1-ol forming an aldehyde and a carboxylic acid. Explain, using a diagram, how the aldehyde can be produced in the laboratory by controlling the reaction conditions. (6)
- Oxidation reaction forming aldehyde
- acid/H+ AND dichromate/Cr2O7 2–
- heat AND distillation
- organic product is butanal/CH3CH2CH2CHO
- CH3CH2CH2CH2OH + [O] – CH3CH2CH2CHO
+H2O - Oxidation reaction forming carboxylic acid
- acid/H+ AND dichromate/Cr2O7 2–
- heat under reflux
- organic product is butanoic acid/
CH3CH2CH2COOH
- CH3CH2CH2CH2OH + 2[O] –
CH3CH2CH2COOH + H2O - Distillation
- diagram of apparatus with condenser
- condenser has water flow
- collection of organic product
- product is separated to prevent further
oxidation (to carboxylic acid)
Suggest the general formula for a carboxylic acid
CnH2nO2
OR
CnH2n+1COOH
State the shape and bond angle around a carbon atom in the alkyl group of propanoic acid. Explain the shape
Tetrahedral
AND
109.5(º)
four bonded pairs repel OR four bonds repel
Suggest a value for the C–O–H bond angle in propanoic acid.
104.5(º)
Compound D is a neutral compound which is a structural isomer of propanoic acid,
CH3CH2COOH.
The infrared spectrum of compound D is shown below
Suggest two possible structures of compound D.
Explain all your reasoning.
C=O. 1630 – 1820 (cm–1 O–H 3200 – 3600 cm–1 O–H Any two structures of compound B from CH3COCH2OH CH2(OH)CH2CHO CH3CH(OH)CHO
2-Chloropropanoic acid, CH3CHClCOOH, can be made by reacting propanoic acid with
chlorine in a radical substitution reaction.
(i) State the conditions for the reaction.
Ultraviolet (radiation)/UV
Write the overall equation for the reaction.
CH3CH2COOH + Cl2 CH3CHClCOOH + HCl
The first step in the reaction mechanism involves homolytic fission of a chlorine molecule
to form two chlorine radicals.
Why is this step an example of homolytic fission?
one electron from the bond (pair) goes to each
atom/chlorine/radica
Write two equations to show the propagation steps in the mechanism for this reaction.
Use dots,•, to show the unpaired electrons on radicals.
Propagation step 1
Cl• + CH3CH2COOH – CH3CHCOOH• + HCl
Propagation step 2
CH3CHCOOH• + Cl2 – CH3CHClCOOH + Cl•
Suggest the structure of intermediate E and the reagent(s) and conditions for step 2.
reagent(s) and conditions …………………………………………………………………………………. [2]
Acid (catalyst) AND heat
The student carries out this synthesis and obtains 1.23 g of pure cyclohexene from 5.50 g
of bromocyclohexane.
Calculate the percentage yield of cyclohexene.
Give your final answer to an appropriate number of significant figures.
Amount cyclohexene (m/M) = 1.23/82 OR 0.0150 mol Amount of bromocyclohexane (m/M) = 5.50/162.9 OR 0.0338 mol % yield = (0.0150/0.0338) 100 = 44.4(%)
