Making soluble salts

A student does a titration to find the volume of phosphoric acid solution (H₃PO₄) needed to neutralise a sample of potassium hydroxide solution (KOH).

One of the products of the reaction is potassium phosphate.

This is the student’s method.

• use a measuring cylinder to transfer 25 cm³ of potassium hydroxide solution to a conical flask

• add two drops of an indicator

• fill a burette with phosphoric acid solution and record the initial reading on the burette

• add the acid to the conical flask

• record the final burette reading when the indicator changes colour

This is the equation for the reaction.

Explain two improvements to the student’s method that would give more accurate results.

The student repeats the titration correctly.

The potassium hydroxide solution has a concentration of 0.150 mol / dm³.

The phosphoric acid solution has a concentration of 0.0400 mol / dm³.

Calculate the volume, in cm³, of phosphoric acid solution needed to neutralise 25.0 cm³ of 0.150 mol / dm³ potassium hydroxide solution.

Give your answer to three significant figures.

Potassium phosphate solution reacts with calcium chloride solution.

One of the products is the insoluble solid, calcium phosphate.

Complete the equation for the reaction.

The student reacts a solution containing 0.0400 mol of potassium phosphate with an excess of calcium chloride solution.

The student obtains 5.70 g of calcium phosphate.

Show that the percentage yield for the reaction is about 90%

[for Ca₃(PO₄)₂ M_r = 310]

Describe how the student can obtain a pure, dry sample of calcium phosphate from the mixture at the end of the reaction.

A student does some titrations to find the volume of dilute nitric acid needed to exactly neutralise 25.0 cm³ of sodium hydroxide solution.

This is the student’s method.

Step 1 add 25.0 cm³ of sodium hydroxide solution to a conical flask

Step 2 add three drops of methyl orange indicator

Step 3 fill a burette with the acid

Step 4 add acid from the burette until the indicator changes colour

Step 5 record the volume of acid added

Give the name of the apparatus that the student should use to measure the volume of sodium hydroxide solution in step 1.

Give the colour change seen in step 4.

Give a reason why the student does not use universal indicator in this titration.

The student completes a rough titration and four accurate titrations.

The diagram shows the burette readings from the rough titration.

The table shows the student’s results.

Complete the table by adding the results from the rough titration.

Record the volumes to the nearest 0.05 cm³

Concordant results are results within 0.20 cm³ of each other.

Use the concordant results from the table to calculate the mean volume of acid added.

This is the equation for the reaction between dilute nitric acid and sodium hydroxide solution.

HNO₃(aq) + NaOH(aq) NaNO₃(aq) + H₂O(l)

After the titration, the student knows the volume of acid needed to neutralise 25.0 cm³ of the sodium hydroxide solution.

Sodium nitrate decomposes at high temperatures.

Describe how the student could obtain pure, dry crystals of sodium nitrate from dilute nitric acid and sodium hydroxide solution.

This question is about magnesium metal and its compounds.

The diagram represents the structure of magnesium.

Complete the diagram by adding the labels.

Explain why magnesium is malleable.

Magnesium burns in oxygen gas to form solid magnesium oxide.

Complete the chemical equation for the reaction by balancing the equation and adding the state symbols.

Give a reason why magnesium is oxidised in this reaction.

A student uses this method to make a solution of magnesium chloride.

Step 1 measure 25 cm³ of dilute hydrochloric acid into a beaker

Step 2 add magnesium powder a little at a time

Step 3 keep adding magnesium powder until it is in excess

Step 4 remove the excess magnesium powder by filtration

This is the equation for the reaction.

Give a reason why the student uses magnesium powder rather than magnesium ribbon.

Give a reason why the student adds an excess of magnesium in step 3.

Calculate the minimum mass of magnesium needed to react with 25.0 cm³ of 2.00 mol / dm³ hydrochloric acid.

[for Mg, A_r = 24]

Sodium sulfate can be prepared by the reaction between sodium hydroxide solution and sodium hydrogensulfate (NaHSO₄) solution.

This is the equation for the reaction.

Sodium hydrogensulfate solution is acidic.

A student adds 25.0 cm³ of sodium hydroxide solution to a conical flask and adds two drops of indicator.

The student does a titration.

Name a piece of apparatus that should be used to add 25.0 cm³ of sodium hydroxide solution to the conical flask.

Describe the method the student should use to find the accurate volume of sodium hydrogensulfate solution needed to neutralise the 25.0 cm³ of sodium hydroxide solution.

The student repeats the titration without the indicator and forms a solution of sodium sulfate.

Describe how the student can obtain pure, dry crystals of hydrated sodium sulfate from the solution.

Crystals of hydrated sodium sulfate decompose when heated.

This is the equation for the decomposition.

A student uses this apparatus to find the value of x.

The student heats the crystals until the decomposition is complete.

The table shows the student’s results.

Use the results to calculate the value of x.

[for Na₂SO₄, M_r = 142 for H₂O, M_r = 18]

A scientist reacts lead(II) nitrate solution with sodium bromide solution.

This is the equation for the reaction.

Pb(NO₃)₂(aq) + 2NaBr(aq) PbBr₂(s) + 2NaNO₃(aq)

Describe how the scientist could obtain a pure dry sample of lead(II) bromide (PbBr₂) from the reaction mixture.

The scientist reacts an excess of lead(II) nitrate solution with 25 cm³ of sodium bromide solution of concentration 2.0 mol/dm³.

Show that the amount of sodium bromide used is 0.050 mol.

Show that the maximum theoretical mass of lead(II) bromide is approximately 9 g.

[for PbBr₂ M_r = 367]

The scientist electrolyses molten lead(II) bromide using this apparatus.

Explain why lead(II) bromide needs to be molten rather than solid for electrolysis to occur.

The electrolyte is at a temperature of 400C.

Explain a suitable material for the electrodes.

Give the half‑equation that occurs at the negative electrode.

Bromine forms at the positive electrode.

This is the half‑equation for the reaction at the positive electrode.

State what is observed at the positive electrode.

State why the half‑equation represents an oxidation reaction.

This method is used in an experiment to produce hydrated zinc nitrate crystals.

• pour 50 cm³ of dilute nitric acid into a beaker

• add a spatula of zinc powder to the acid

• add more zinc until it is in excess

• filter the mixture

• obtain crystals of zinc nitrate from the filtrate

State why the mixture is filtered.

Describe how a pure, dry sample of hydrated zinc nitrate crystals could be obtained from the filtrate.

This equation represents the formation of hydrated zinc nitrate in the experiment.

In another experiment, 9.75 g of zinc is completely reacted with nitric acid.

Show that the maximum possible mass of hydrated zinc nitrate crystals that could be formed is approximately 45 g.

[for Zn(NO₃)₂.6H₂O, M_r = 297]

The actual yield of hydrated zinc nitrate crystals is 36.4 g.

Calculate the percentage yield of hydrated zinc nitrate crystals.

The box gives some methods that are involved in the separation of mixtures.

Use words from the box to identify the method involved in each of these separations.

Give the best method for obtaining gasoline from crude oil.

Give the best method for separating the dyes in black ink.

Give the best method for obtaining pure water from seawater.

A sample of solid hydrated copper(II) sulfate can be obtained from a mixture of copper(II) oxide and copper(II) sulfate.

Complete the passage by using words from the box.

The mixture of copper(II) oxide and copper(II) sulfate can be separated by first

_........ the copper(II) sulfate in distilled water.

The copper(II) oxide is then removed by

Some of the water from the copper(II) sulfate solution is then removed by

A pure sample of hydrated copper(II) sulfate is then obtained by

When solutions of lead(II) nitrate and potassium chloride are mixed, a precipitate of lead(II) chloride forms.

Complete the equation for the reaction by adding the state symbols.

Give the formula of each ion in lead(II) nitrate.

lead ion

nitrate ion

Calculate the relative formula mass (M_r) of lead(II) nitrate, Pb(NO₃)₂

A student investigates the height of the precipitate formed when lead(II) nitrate solution is added to potassium chloride solution.

This is the student’s method.

Step 1&$pour=NRKM cm³ of potassium chloride solution into a boiling tube

Step 2&$~dd=OKM cm³ of lead(II) nitrate solution and allow the precipitate to settle

Step 3 measure the height of the precipitate

Repeat steps 2 and 3 until a total of 14.0 cm³ of lead(II) nitrate solution has been added.

The table shows the student’s results.

Plot the results on the grid.

Draw a circle around the anomalous result.

Draw a line of best fit through the first four points and another line of best fit through the last three points. Make sure that the lines cross.

Volume of lead(II) nitrate in cm³

Give two possible mistakes the student could have made to cause the anomalous result.

State why the first line of best fit should pass through the origin.

Use your graph to determine the volume of lead(II) nitrate solution needed to react completely with 15.0 cm³ of potassium chloride solution.

This question is about the insoluble salt, lead(II) bromide.

Lead(II) bromide can be made by a precipitation reaction.

This is the equation for the reaction.

Pb(NO₃)₂(aq) + 2KBr(aq) PbBr₂(s) + 2KNO₃(aq)

Describe how solutions of lead nitrate and potassium bromide can be used to make a pure, dry sample of lead(II) bromide.

A solution containing 0.150 mol of lead(II) nitrate is reacted with an excess of potassium bromide solution.

A mass of 49.6 g of pure, dry lead(II) bromide is produced.

Show, by calculation, that the percentage yield of lead(II) bromide is 90.1%.

[for PbBr₂, M_r = 367]

A student investigates the change in electrical conductivity as dilute lead(II) nitrate solution is added to dilute potassium bromide solution.

This is the student’s method.

Step 1add 50 cm³ of potassium bromide solution to a beaker

Step 2 measure the electrical conductivity of the solution

Step 3add 10 cm³ of lead(II) nitrate solution to the beaker

Step 4 stir the mixture

Step 5 measure the electrical conductivity of the mixture

Repeat steps 3, 4 and 5 until a total of 50 cm³ of lead(II) nitrate solution has been added.

The table shows the student’s results.

Plot the student’s results on the grid.

Draw a line of best fit, ignoring the anomalous result.

Total volume of lead(II) nitrate in cm³

Explain the shape of the graph.

Suggest a mistake the student could have made to cause the anomalous result.

Further 10 cm³ volumes of lead(II) nitrate are added to the beaker so the lead(II) nitrate is in excess.

Predict what will happen to the conductivity of the mixture when the lead(II) nitrate is in excess.

The diagram shows the electrolysis of molten lead(II) bromide, PbBr₂

This is the ionic half‑equation for the formation of bromine at electrode A.

Give a reason why this half‑equation shows oxidation.

A student uses the reaction between zinc powder and dilute nitric acid to prepare some zinc nitrate crystals.

Complete the equation for the reaction by adding the state symbols.

State what the student would observe during this reaction.

In the preparation, the student adds an excess of zinc powder to some dilute nitric acid.

State why the student uses an excess of zinc powder.

Describe what the student should do next to obtain pure, dry crystals of zinc nitrate.

The formula for the zinc nitrate crystals is Zn(NO₃)₂.6H₂O

When zinc nitrate crystals are heated, the products are zinc oxide, nitrogen dioxide (NO₂), oxygen and water.

Complete the equation for this reaction.

This question is about the reaction between magnesium and dilute nitric acid.

A student reacts dilute nitric acid with an excess of magnesium powder as a first step in the preparation of dry crystals of hydrated magnesium nitrate.

This is the equation for the reaction.

Explain why it is important that magnesium is in excess.

The student adds 0.75 g of magnesium to 0.025 mol of nitric acid.

Calculate the mass of magnesium, in grams, that remains at the end of the reaction.

[for magnesium, A_r = 24]

Describe how the student can obtain dry crystals of hydrated magnesium nitrate from the mixture at the end of the reaction.

The student repeats the experiment and records the volume of hydrogen gas collected.

The graph shows the student’s results.

Use the graph to calculate the rate of reaction, in cm³/ s, at t = 40 s.

Show your working on the graph.

This question is about soluble salts and insoluble salts.

Which pair of solutions produces an insoluble salt when mixed?

When solutions of lead nitrate and sodium sulfate are mixed, one product is solid lead sulfate.

This is the equation for the reaction.

Describe how a pure, dry sample of solid lead sulfate can be obtained from the mixture.

The table gives the solubility of a salt in water at six different temperatures.

Plot the points on the grid.

Draw a curve of best fit.

A saturated solution of the salt in 100 g of water is cooled from 90C to 30C.

Use your graph to determine the mass of salt that will crystallise.

Show your working on the graph.

A student uses this method to do a titration.

• use a measuring cylinder to obtain 25 cm³ of sodium hydroxide solution

• transfer the solution to a conical flask

• add a few drops of universal indicator to the flask

• fill a burette with dilute sulfuric acid and record the initial burette reading

• add the acid to the flask, swirling the flask continuously

• add the acid slowly near the end‑point

• record the final burette reading at the end‑point

The student repeats the titration until at least two concordant results are obtained.

State what is meant by concordant results.

Explain two improvements to the student’s method so that more accurate results are obtained.

The student makes the improvements and repeats the titration.

The sulfuric acid has a concentration of 0.600 mol/dm³.

The sodium hydroxide solution has a concentration of 1.50 mol/dm³.

This is the equation for the reaction.

Calculate the volume, in cm³, of sulfuric acid that the student needs to completely react with 25.0 cm³ of the sodium hydroxide solution.

The student plans to obtain pure dry crystals of hydrated sodium sulfate.

They add the calculated volume of sulfuric acid to 25.0 cm³ of the sodium hydroxide solution to form sodium sulfate solution.

Describe what the student should do to obtain pure dry crystals of hydrated sodium sulfate from the solution.

This question is about soluble and insoluble compounds.

A precipitate is an insoluble compound formed when solutions of soluble compounds react after mixing.

Different solutions are mixed in separate test tubes.

Tube 1 copper(II) sulfate solution and calcium chloride solution

Tube 2 magnesium nitrate solution and potassium sulfate solution

Tube 3 sodium carbonate solution and copper(II) sulfate solution

In which of the tubes will a precipitate form?

A student mixes solutions, containing equal amounts in moles, of silver nitrate and sodium chloride.

The equation for the reaction between silver nitrate solution and sodium chloride solution is

AgNO₃(aq) + NaCl(aq) AgCl(s) + NaNO₃(aq)

State the colour of the precipitate of silver chloride.

The student wants to obtain pure, dry crystals of sodium nitrate.

Crystals of sodium nitrate decompose at temperatures above 300 °C.

Describe a method the student could use to obtain pure, dry crystals of sodium nitrate.

Give an advantage of mixing solutions containing equal amounts, in moles, of silver nitrate and sodium chloride.

A teacher prepares the insoluble salt lead(II) bromide (PbBr₂) by mixing solutions of lead(II) nitrate and sodium bromide.

Describe what the teacher should do next to obtain a pure, dry sample of lead(II) bromide.

The teacher then sets up a circuit in a fume cupboard using the pure, dry sample of lead(II) bromide.

Explain why the lamp does not light when the lead(II) bromide is solid.

The teacher heats the lead(II) bromide.

When the lead(II) bromide is molten, the lamp lights and bromine forms at the positive electrode.

State what observation would be made at the positive electrode.

Explain how bromide ions in the molten lead(II) bromide become bromine molecules at the positive electrode.

Write an ionic half-equation for the reaction that occurs at the negative electrode.

Include state symbols in your equation.

This question is about salts.

Soluble salts can be prepared by the reaction between a metal oxide and an acid.

The equation for this type of reaction is

metal oxide + acid salt + water

State the name given to this type of reaction.

State, in terms of protons, what happens in this reaction.

A student is given 50 cm³ of dilute sulfuric acid and a bottle of solid copper(II) carbonate.

Describe the method that the student should use to prepare a saturated solution of copper(II) sulfate.

In your answer, refer to the pieces of apparatus that the student should use.

The student produces dry crystals of hydrated copper(II) sulfate from the saturated solution.

He calculates that 6.40 g of dry crystals should be formed.

The mass of dry crystals he actually obtains is 1.80 g less than he calculated.

Calculate the student’s percentage yield.

Give your answer to one decimal place.

Gypsum is hydrated calcium sulfate.

A sample of gypsum contains 79% of calcium sulfate by mass.

Calculate the value of x in CaSO₄.xH₂O

Describe a test for calcium ions in the sample of gypsum.

This question is about the insoluble salt silver chloride (AgC l).

Silver chloride can be made by the reaction between copper(II) chloride and silver nitrate.

Describe how a student could prepare a pure, dry sample of silver chloride starting with copper(II) chloride solution and silver nitrate solution.

A student investigates the quantity of silver chloride produced when different volumes of silver nitrate solution are added to copper(II) chloride solution.

This is the student’s method. pour 5.0 cm³ of copper(II) chloride solution into a test tube add 1.0 cm³ of silver nitrate solution to the test tube

allow the silver chloride precipitate to settle

measure the height of the precipitate

The student repeats the method using different volumes of silver nitrate solution.

The table shows the student’s results.

Plot the student’s results.

Draw two straight lines of best fit, ignoring the anomalous result.

Volume of silver nitrate added in cm³

Suggest a mistake the student made to cause the anomalous result.

Give a reason why the last three heights are the same.

The equation for the reaction between copper(II) chloride and silver nitrate is

CuCl₂(aq) + 2AgNO₃(aq) 2AgCl(s) + Cu(NO₃)₂(aq)

A student measures 25.0 cm³ of 0.500 mol/dm³ copper(II) chloride solution and reacts it with silver nitrate solution.

Name a piece of apparatus suitable for measuring 25.0 cm³ of copper(II) chloride solution.

Calculate the maximum mass, in grams, of silver chloride that could be produced.

[M_r of AgCl = 143.5]

In an experiment using different solutions, the mass of silver chloride produced is 0.744 g.

The maximum mass of silver chloride that could be produced is 0.850 g.

Calculate the percentage yield.

A student uses the reaction between zinc and dilute sulfuric acid to prepare some zinc sulfate crystals.

Complete the equation for this reaction by giving the correct state symbols.

State what would be observed during this reaction.

The student adds excess zinc to a beaker of dilute sulfuric acid.

Explain why it is necessary to add excess zinc.

Draw a diagram of the apparatus the student should use to remove the unreacted zinc and collect the zinc sulfate solution.

The student obtains a pure, dry sample of zinc sulfate crystals.

The formula of zinc sulfate crystals is ZnSO₄.7H₂O

Calculate the relative molecular mass (M_r) of zinc sulfate crystals.

The student uses 0.0200 mol of dilute sulfuric acid in her preparation.

Show that the maximum mass of zinc sulfate crystals that the student could obtain is about 6 g.

The student obtains a mass of 4.28 g of zinc sulfate crystals.

Calculate the percentage yield of the zinc sulfate crystals.

Give your answer to three significant figures.

The table gives information about some lead compounds.

When a sample of red lead oxide is heated, it changes into a yellow solid and a gas forms that relights a glowing splint.

Complete the word equation for this reaction.

red lead oxide _........ +_........

A sample of one of the oxides of lead contains 86.6% lead and 13.4% oxygen by mass.

Show by calculation that the sample is lead(IV) oxide, PbO₂

[A_r of Pb = 207 A_r of O = 16]

Red lead oxide reacts with warm dilute nitric acid.

Complete the chemical equation for the reaction.

Pb₃O₄(_........ ) + 4HNO₃(_........ ) _........ Pb(NO₃)₂(aq) + PbO₂(s) +_........ H₂O(l)

A student is given a sample of solid red lead oxide and some dilute nitric acid.

Describe how the student could obtain a pure dry sample of lead(II) nitrate crystals.

A student wants to prepare sodium chloride crystals from sodium hydroxide solution and dilute hydrochloric acid.

He does a titration to find the volume of dilute hydrochloric acid needed to neutralise the sodium hydroxide solution.

This is his method.

● add 25.0 cm³ of sodium hydroxide solution to a conical flask

● add a few drops of phenolphthalein indicator to the conical flask

● titrate the solution with the hydrochloric acid

Name a suitable piece of apparatus that the student should use to measure 25.0 cm³ of sodium hydroxide solution.

Give the colour of the phenolphthalein indicator in sodium hydroxide solution and in hydrochloric acid.

colour in sodium hydroxide solution_........

colour in hydrochloric acid_........

Suggest why universal indicator is never used in a titration.

The student finds that 21.50 cm³ of hydrochloric acid is needed to neutralise 25.0 cm³ of sodium hydroxide solution.

Describe what the student should do next to prepare a pure solution of sodium chloride.

Describe how the student could obtain dry crystals of sodium chloride from the pure sodium chloride solution.

The student needs 21.50 cm³ of hydrochloric acid to neutralise 25.0 cm³ of sodium hydroxide solution of concentration 0.800 mol/dm³.

The equation for the reaction is

Calculate the concentration, in mol/dm³, of the hydrochloric acid.

concentration =_........ mol/dm

Solutions of silver nitrate and potassium chloride react together to make the insoluble salt, silver chloride.

A student uses this method to prepare a sample of silver chloride.

Step 1 add 25 cm³ of silver nitrate solution to a conical flask

Step 2 add potassium chloride solution to the flask

Step 3 filter off the silver chloride

What term is used for this reaction?

Give two more steps that will produce a pure, dry sample of silver chloride.

Acidified silver nitrate solution is used to test for chloride ions.

Give a reason why hydrochloric acid is not used to acidify silver nitrate solution.

The chemical equation for the reaction between solutions of silver nitrate and potassium chloride is

AgNO₃(aq) + KCl(aq) AgCl(s) + KNO₃(aq)

A student adds an excess of potassium chloride solution to 25.0 cm³ of 0.100 mol/dm³ silver nitrate solution.

Calculate the maximum mass of silver chloride, in grams, that can be produced.

[M_r of AgCl = 143.5]

This question is about some Group 2 elements and their compounds.

Calcium reacts with water to produce calcium hydroxide and hydrogen gas.

Give the word equation for this reaction.

State two observations that would be made during this reaction.

Describe how a pure, dry sample of the insoluble salt, barium sulfate, could be made from the two solids sodium sulfate and barium chloride.

Give an ionic equation for the reaction that occurs.

Include state symbols in your equation.

When magnesium nitrate is heated, magnesium oxide, nitrogen dioxide and oxygen form.

The equation for the reaction is

What is the name for this type of reaction?

Calculate the total volume, in dm³, of gas produced at rtp when 7.7 g of magnesium nitrate completely reacts.

[Assume that the molar volume of a gas at rtp is 24 dm³]

[M_r of Mg(NO₃)₂ = 148]

Give your answer to two significant figures.