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Context for question 1

Solid X is a mixture of three salts, potassium chloride, KCl, sodium chloride, NaCl, and sodium nitrate, NaNO

_{3}

, only. The mass of each substance in X is investigated by two experiments. In each experiment, a different ion is precipitated out of an aqueous solution of X. The mass of each precipitate is measured.

1(a)Tables Graphs Data AnalysisEasy1 mark

A student weighs a sample bottle containing X and transfers X into a small beaker. The student reweighs the sample bottle. The measurements are shown in Table 1.1.

Complete Table 1.1 to determine the mass of X in the small beaker.

measurement	value
mass of sample bottle and X / g	7.235
mass of sample bottle after transfer / g	6.035
mass of X transferred to small beaker / g	Table answer r3_value

1(b)(i)Uncertainty Errors EvaluationEasy1 mark

Calculate the percentage error in the measurement of the mass of the sample bottle and X shown in Table 1.1. Show your working.

Draw with the mouse or a finger.

1(b)(ii)Uncertainty Errors EvaluationEasy1 mark

Without changing any apparatus, suggest how the percentage error calculated in 1(b)(i) can be reduced.

1(c)Volumetric Techniques Titration PracticeMedium3 marks

Describe the steps the student should take to prepare 250.0 cm

^{3}

of an aqueous solution of X, starting from the mass of X calculated in 1(a) supplied in the small beaker. Give the name and capacity of any apparatus used. Write your answer using a series of numbered steps.

Answer

0 words

Context for 1(d)

Aqueous sodium tetraphenylborate, NaB(C

_{6}

H

_{5}

)

_{4}

(aq), reacts with aqueous potassium ions to form a precipitate. The ionic equation for this reaction is shown.

B(C_{6} H_{5})_{4}^{-} (aq) + K^{+} (aq) \to KB(C_{6} H_{5})_{4} (s)

KB(C

_{6}

H

_{5}

)

_{4}

(s) is an irritant. Figure 1.1 shows a Gooch crucible with a porous glass disc. The porous glass disc acts as a fine filter to separate the precipitate from the aqueous reaction mixture.

Figure 1.1, a Gooch crucible: a squat cylindrical glass vessel that tapers slightly towards its base, containing a shallow shaded porous glass disc set horizontally near the bottom, labelled porous glass disc with a leader line to the disc

The solution formed from solid X in 1(c) is labelled solution X. In the first experiment, the student carries out the following steps.

1
Transfer 25.0 cm $^{3}$ of solution X to a 250 cm $^{3}$ conical flask labelled D.
2
Use a measuring cylinder to add approximately 40 cm $^{3}$ of 0.0180 mol dm $^{- 3}$ NaB(C $_{6}$ H $_{5}$ ) $_{4}$ (aq) to conical flask D. Stir slowly as the precipitate forms. Leave conical flask D in an ice bath for 20 minutes.
3
Place a clean Gooch crucible in an oven at $120^{\circ} C$ .
4
After 20 minutes, remove the Gooch crucible from the oven, allow to cool and record its mass.
5
Pour the mixture from conical flask D into the Gooch crucible and filter.
6
Wash the residue in the Gooch crucible.
7
Transfer the Gooch crucible and residue to the oven and leave for one hour at $120^{\circ} C$ .
8
Remove the Gooch crucible from the oven and allow to cool. Record the mass of the Gooch crucible and the residue.

1(d)(i)Practical Techniques SafetyEasy1 mark

Other than wearing safety goggles, give one safety precaution that the student must take when handling KB(C

_{6}

H

_{5}

)

_{4}

(s).

1(d)(ii)Practical Techniques SafetyEasy1 mark

Identify a suitable piece of apparatus to transfer 25.0 cm

^{3}

of solution X in step 1.

1(d)(iii)Practical Techniques SafetyEasy1 mark

Suggest why the volume of NaB(C

_{6}

H

_{5}

)

_{4}

(aq) does not need to be measured accurately in step 2.

1(d)(iv)Practical Techniques SafetyEasy1 mark

Suggest one reason why conical flask D is kept cool in an ice bath in step 2.

1(d)(v)Practical Techniques SafetyEasy1 mark

Suggest one reason why the Gooch crucible is placed in an oven at

120^{\circ} C

in step 3.

1(d)(vi)Mass CalculationsMedium1 mark

The mass of residue is 0.3579 g. Calculate the amount, in mol, of potassium ions, K

^{+}

, in solid X in the small beaker in 1(a). [

M_{r}

: KB(C

_{6}

H

_{5}

)

_{4}

, 357.9]

Amount of K

^{+}

in solid X

1(d)(vii)Mass CalculationsMedium1 mark

Use your answer to 1(d)(vi) to determine the mass of KCl in solid X.

Mass of KCl in solid X

Context for 1(e)

Aqueous silver nitrate, AgNO

_{3}

(aq), reacts with aqueous chloride ions, Cl

^{-}

(aq), to form a precipitate of silver chloride, AgCl(s). The ionic equation for this reaction is shown.

Ag^{+} (aq) + Cl^{-} (aq) \to AgCl(s)

In a second experiment, the student repeats steps 1 to 8 using aqueous silver nitrate, AgNO

_{3}

(aq), instead of NaB(C

_{6}

H

_{5}

)

_{4}

(aq). The mass of AgCl(s) recorded in step 8 is 0.2151 g. The amount,

n

, in mol, of NaCl in solid X can be calculated using equation 1.

n = Q - amount, in mol, of K^{+} in solid X in 1(d)(vi)

Q

is the amount, in mol, of AgCl(s) produced when all the Cl

^{-}

(aq) ions in 250 cm

^{3}

of solution X react with AgNO

_{3}

(aq).

1(e)(i)Mass CalculationsMedium1 mark

Calculate

Q

.

Q

1(e)(ii)Mass CalculationsMedium1 mark

Use equation 1 to calculate the mass, in g, of NaCl in solid X. If you were unable to obtain an answer to 1(e)(i), use

Q = 0.014

mol. This is not the correct answer.

Mass of NaCl in solid X

1(e)(iii)Mass CalculationsMedium1 mark

Calculate the mass of NaNO

_{3}

in solid X using your answers to 1(d)(vii), 1(e)(ii) and the information given.

Mass of NaNO

_{3}

in solid X

1(f)Uncertainty Errors EvaluationMedium1 mark

Show the effect, if any, on the calculated masses of KCl and NaCl if the residue of KB(C

_{6}

H

_{5}

)

_{4}

was not washed in step 6 of the first experiment.

Effect on the calculated mass of KCl in 1(d)(vii)

Effect on the calculated mass of NaCl in 1(e)(ii)

1(g)Uncertainty Errors EvaluationMedium1 mark

Another student repeated the first experiment but heated the Gooch crucible to

320^{\circ} C

in step 7. Suggest why the mass of precipitate collected by this student was significantly lower than the mass of precipitate collected by the first student.

February/March 2026 Paper 52

Questions