(cid:44)(cid:1)(cid:1)(cid:1)(cid:1)(cid:9)(cid:1)(cid:1)(cid:1)(cid:1)(cid:1)(cid:1)(cid:1)(cid:7)(cid:44)
(c) LCA10 is a different form of LCA caused by a recessive mutation in the CEP290 gene.
This gene codes for the protein CEP290, which is involved in the correct functioning of
photoreceptor cells in the retina.
The mutation in CEP290 causes an error to be made when the primary transcript is spliced to
form messenger RNA (mRNA). The abnormal mRNA that is formed has an extra sequence of
RNA nucleotides, known as exon X, between exon 26 and exon 27. Exon X contains a STOP
codon.
Fig. 3.1 compares the effect of the mutation in CEP290 with the normal gene expression.
normal LCA10
exon intron exon section of DNA exon mutation exon
of CEP290
(a) DCPIP is an indicator and can be used to determine the rate of respiration of organisms such
as yeast.
(i) State the category of indicators to which DCPIP belongs.
..................................................................................................................................... [1]
(ii) Describe the colour change that occurs in DCPIP during experiments to determine the
rate of respiration.
..................................................................................................................................... [1]
(b) An investigation was carried out to determine the effect of temperature on the rate of
respiration of yeast.
• A suspension of yeast cells was added to a test‑tube containing glucose solution.
• A further four test‑tubes were set up in the same way.
• One test‑tube was placed in a water‑bath at 10 °C for 5 minutes.
• DCPIP was added to the test‑tube and the time taken for the DCPIP to change colour
was measured.
• The experiment was repeated using the other test‑tubes at 20° C, 30 °C, 40 °C and 50 °C.
The results are shown in Fig. 6.1.
Magnesium has three naturally occurring isotopes: ²⁴Mg, ²⁵Mg and ²⁶Mg.
(a) Explain what is meant by the term isotopes.
(b) The percentage abundances of ²⁴Mg and ²⁵Mg are 79.0% and 10.0% respectively. Calculate the relative atomic mass of magnesium, giving your answer to 3 significant figures.
0 cm3 of 0.100 mol dm –3 sodium iodide.
The volume remains constant at 25.0 cm3.
The mixture is left to reach equilibrium at room temperature.
Ice-cold water is added to freeze the position of equilibrium and the mixture is
then titrated with standard silver nitrate solution.
The whole mixture requires 12.20 cm3 of 0.0500 mol dm –3 silver nitrate solution to
react with the aqueous iodide ions at equilibrium.
Ag + (aq) + I – (aq) → AgI(s)
Calculate the equilibrium concentrations of the sulfate ions and the iodide ions,
and hence the value of K at room temperature.
c
Give your answer to an appropriate number of significant figures and include
units for K , if any.
c
(7)
Question
Mathematics
Edexcel2021
*P65463A01828*
PPMMTT
(d) Propanoic acid is a weak acid.
(i) Calculate the pH of a 0.100 mol dm–3 solution of propanoic acid at 298 K.
Give your answer to an appropriate number of significant figures.
[K = 1.35 × 10–5 mol dm–3 at 298 K]
a
(3)
(ii) State two assumptions that you made in the calculation in d(i).
(2)
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Question
Mathematics
Edexcel2020
Give your answer to an appropriate number of significant figures.
(5)
Question
Mathematics
Edexcel2019
0 cm3 of an ethanoic acid solution of concentration 0.800 mol dm–3 to form this
buffer solution.
Give your answer to an appropriate number of significant figures.
[K for ethanoic acid = 1.74 × 10–5 mol dm–3]
a
(5)
Question
Mathematics
Edexcel2018
*P52302RA0528*
Turn over
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DO
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NI
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TON
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(b) Calculate the enthalpy change of neutralisation for the reaction between nitric acid
and sodium hydroxide solution, using the results of the experiment.
Give your answer to an appropriate number of significant figures.
Assume: density of the reaction mixture = 1.0 g cm−3
specific heat capacity of the reaction mixture = 4.18 J g−1 °C−1
(4)
(Total for Question 3 = 5 marks)
Question
Mathematics
Edexcel2017
0 cm3 of 1.00 mol dm–3 aqueous ammonia.
Give your answer to an appropriate number of significant figures.
[Assume: the density of the solution is 1.00 g cm–3 ]
the specific heat capacity of the solution is 4.18 J g–1 (cid:113)C–1
(3)