AS & A Level Chemistry - 9701 Paper 3 2019 Summer Zone 2

Amidosulfonic acid is a monoprotic acid with the formula $\text{HSO}_x\text{NH}_2$. In this experiment you will determine the value of $x$ in the formula by titration with an alkali.

FB 1 is amidosulfonic acid, $\text{HSO}_x\text{NH}_2$. You are supplied with approximately 3.0g.
FB 2 is 0.110 mol dm^-3 sodium hydroxide, NaOH.
thymolphthalein indicator

(a) Method

Preparing a solution of amidosulfonic acid

• Weigh the empty beaker. Record the mass.
• Add 2.50–2.70 g of FB 1 to the beaker. Weigh the beaker and its contents. Record the mass.
• Calculate and record the mass of FB 1 used.
• Add approximately 100 cm³ of distilled water to the beaker and stir to dissolve FB 1.
• Transfer the solution to the 250 cm³ volumetric flask.
• Rinse the beaker twice with approximately 20 cm³ of distilled water each time and add to the volumetric flask.
• Add distilled water to the volumetric flask to make 250 cm³ of solution.
• Shake the volumetric flask to mix the solution thoroughly and label it FB 3.

Titration of FB 3

• Fill the burette with FB 2.
• Pipette 25.0 cm³ of FB 3 into a conical flask.
• Add a few drops of thymolphthalein to the conical flask.
• Carry out a rough titration.
• Record your burette readings and the rough titre in the space below.

The rough titre is ............................... cm³.

• Carry out as many accurate titrations as you think necessary to obtain consistent results.
• Make sure any recorded results show the precision of your practical work.
• Record all of your burette readings and the volume of FB 2 added in each accurate titration.

(b) From your accurate titration results, obtain a suitable value for the volume of FB 2 to be used in your calculations.
Show clearly how you obtained this value.

25.0 cm³ of FB 3 required ............................... cm³ of FB 2. [1]

(c) Calculations

(i) Give your answers to (ii), (iii), (iv) and (v) to the appropriate number of significant figures. [1]

(ii) Calculate the number of moles of sodium hydroxide, NaOH, in the volume of FB 2 calculated in (b).

moles of NaOH = ................................ mol [1]

(iii) One mole of sodium hydroxide neutralises one mole of amidosulfonic acid.

Complete the equation for the reaction of amidosulfonic acid with sodium hydroxide.
Include state symbols.
......NaOH(......) + ......$\text{HSO}_x\text{NH}_2$(......) → .................................. + ..................................

State the number of moles of amidosulfonic acid that reacted with the number of moles of NaOH calculated in (ii).

moles of $\text{HSO}_x\text{NH}_2$ = ............................... mol [1]

(iv) Use your results on page 2 and your answer to (iii) to calculate the relative formula mass, $M_r$, of amidosulfonic acid.

$M_r$ of amidosulfonic acid = ............................... [1]

(v) Calculate the value of $x$ in the formula of amidosulfonic acid, $\text{HSO}_x\text{NH}_2$.

$x$ = ............................... [1]

(d) The salts produced from amidosulfonic acid are called amidosulfonates.

You are to carry out an experiment using FB 1 to find out if barium amidosulfonate is soluble in water.

• Describe your experiment.
• Record your observation(s) and conclusion.

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When hydrated copper hydroxycarbonate, $\text{CuCO}_3.\text{Cu(OH)}_2.y\text{H}_2\text{O}$ is heated, it decomposes as shown.

$$\text{CuCO}_3.\text{Cu(OH)}_2.y\text{H}_2\text{O(s)} \rightarrow 2\text{CuO(s)} + \text{CO}_2(g) + (1 + y)\text{H}_2\text{O(g)}$$

In this experiment, you will heat hydrated copper hydroxycarbonate to decompose it. You will use your results to investigate the value of $y$.
FB 4 is hydrated copper hydroxycarbonate, $\text{CuCO}_3.\text{Cu(OH)}_2.y\text{H}_2\text{O}$.

(a) Method
• Weigh the crucible with its lid and record the mass.
• Add all the FB 4 from the container into the crucible.
• Weigh the crucible and lid with FB 4 and record the mass.
• Place the crucible and contents on the pipe-clay triangle.
• Heat the crucible and contents gently for approximately two minutes with the lid on.
• Use tongs to remove the lid and heat strongly for approximately three minutes.
• Replace the lid and leave the crucible and residue to cool for several minutes.

While the crucible is cooling, you may wish to begin work on Question 3.
• When the crucible is cool, reweigh it with its lid and contents. Record the mass.
• Calculate and record the mass of FB 4 and the mass of residue obtained.

Results

State the observations made while the decomposition of FB 4 was taking place.
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(b) Calculations
(i) Calculate the number of moles of copper oxide, CuO, obtained as residue.
moles of CuO obtained = ................................ mol [1]

(ii) Use your results to calculate the relative formula mass, $M_r$, of hydrated copper hydroxycarbonate, $\text{CuCO}_3.\text{Cu(OH)}_2.y\text{H}_2\text{O}$.

$M_r \text{ of CuCO}_3.\text{Cu(OH)}_2.y\text{H}_2\text{O} = ................................$ [2]

(iii) Use the Periodic Table to calculate the relative formula mass of $\text{CuCO}_3.\text{Cu(OH)}_2$.

$M_r \text{ of CuCO}_3.\text{Cu(OH)}_2 = ................................$

Use your answer to (ii) and this $M_r$ to comment on the value of $y$ in the formula of hydrated copper hydroxycarbonate.
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[2]

(c) State one way to improve the accuracy of the experiment, using the same mass of FB 4.
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[1]

(a) FB 5 contains one cation and one anion from those listed in the Qualitative Analysis Notes.

(i) Transfer a small spatula measure of FB 5 into a hard-glass test-tube. Heat gently at first and then heat strongly, until no further change occurs.

Record all your observations.
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(ii) To a 1 cm depth of dilute hydrochloric acid in a test-tube, add a small spatula measure of FB 5.

Record your observations.
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(iii) Deduce the formula of FB 5.
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(b) FB 6 is a solution of a compound containing one cation from those listed in the Qualitative Analysis Notes.

(i) Carry out the following tests using a 1 cm depth of FB 6 in a test-tube for each test.

[Table_1]

Add two drops of Universal Indicator solution.

Add an equal volume of aqueous manganese(II) chloride.

Add an equal volume of dilute sulfuric acid.

Add a few drops of aqueous silver nitrate, then
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add aqueous ammonia.
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Add a few drops of aqueous copper(II) sulfate, then
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add excess dilute hydrochloric acid.
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(ii) What can be determined about FB 6 from its reaction with manganese(II) chloride?
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(iii) Give the ionic equation for the reaction between FB 6 and sulfuric acid. Include state symbols.
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(iv) When aqueous copper(II) sulfate was added to FB 6, two precipitates were formed.
Deduce the identity of the two precipitates.
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Explain the observation you made when you added excess dilute hydrochloric acid in the final test of (b)(i).
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