(a) A hydrated salt, compound A, is analysed and has the following percentage composition by mass: Cr. 19.51%; Cl, 39.96%; H, 4.51%; O, 36.02%. Calculate the formula of compound A, showing clearly the water of crystallisation. Show your working.

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7.
22 This question is about several salts.
(a) A hydrated salt, compound A, is analysed and has the following percentage composition by
mass:
Cr, 19.51%; CI, 39.96%; H, 4.51%; O, 36.02%.
Calculate the formula of compound A, showing clearly the water of crystallisation.
Show your working.
formula of compound A =
(b) A student carries out an experiment to determine the amount of water of crystallisation in
the formula of another hydrated salt. The student intends to remove the water by heating the
hydrated salt.
A diagram of the apparatus used by the student is shown below.
crucible
pipeclay triangie
The student adds the hydrated salt to the crucible and weighs the crucible and contents.
The student heats the crucible and contents and allows them to cool.
The student weighs the crucible and residue.
The student's results are shown below.
16,84
Mass of crucible + hydrated salt/g
16.26
Mass of crucible + residue after heating/g
Transcribed Image Text:7. 22 This question is about several salts. (a) A hydrated salt, compound A, is analysed and has the following percentage composition by mass: Cr, 19.51%; CI, 39.96%; H, 4.51%; O, 36.02%. Calculate the formula of compound A, showing clearly the water of crystallisation. Show your working. formula of compound A = (b) A student carries out an experiment to determine the amount of water of crystallisation in the formula of another hydrated salt. The student intends to remove the water by heating the hydrated salt. A diagram of the apparatus used by the student is shown below. crucible pipeclay triangie The student adds the hydrated salt to the crucible and weighs the crucible and contents. The student heats the crucible and contents and allows them to cool. The student weighs the crucible and residue. The student's results are shown below. 16,84 Mass of crucible + hydrated salt/g 16.26 Mass of crucible + residue after heating/g
15
(i) The maximum error in each mass measurement using the balance is 10.005 g.
Calculate the percentage error in the mass of water removed.
percentage error =
(ii) Suggest one modification that the student could make to their method to reduce the
percentage error in the mass of water removed.
(iii) The student is not sure that all the water of crystallisation has been removed.
How could the student modify the experiment to be confident that all the water of
crystallisation has been removed?
Transcribed Image Text:15 (i) The maximum error in each mass measurement using the balance is 10.005 g. Calculate the percentage error in the mass of water removed. percentage error = (ii) Suggest one modification that the student could make to their method to reduce the percentage error in the mass of water removed. (iii) The student is not sure that all the water of crystallisation has been removed. How could the student modify the experiment to be confident that all the water of crystallisation has been removed?
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