Making soluble salts

Silver nitrate and potassium chloride are ionic compounds that are soluble in water.

When potassium chloride solution is added to a solution of silver nitrate, a white precipitate forms.

Complete the equation for this reaction, including the missing state symbol.

Give the name of the white precipitate that forms.

State and explain how the white precipitate can be separated from the reaction mixture.

Silver nitrate solution conducts electricity. Solid silver also conducts electricity.

Describe how silver nitrate solution conducts electricity and how solid silver conducts electricity.

A bottle containing an unknown solution is labelled with the two hazard symbols shown in Figure 16.

What are the meanings of these two symbols?

State a safety step that should be taken when using the unknown solution.

Silver nitrate and potassium chloride are ionic compounds that are soluble in water.

When potassium chloride solution is added to a solution of silver nitrate, a white precipitate forms.

Complete the equation for this reaction, including the missing state symbol.

Give the name of the white precipitate that forms.

State and explain how the white precipitate can be separated from the reaction mixture.

Silver nitrate solution conducts electricity. Solid silver also conducts electricity.

Describe how silver nitrate solution conducts electricity and how solid silver conducts electricity.

A 250 cm³ solution of copper sulfate contains 6.52 g of dissolved solid.

Calculate the concentration of this copper sulfate solution in g dm^–3.

concentration =_........ g dm

Sodium hydroxide solution and copper sulfate solution were reacted together completely.

The result was a mixture of a precipitate of copper hydroxide in a solution of sodium sulfate.

Describe how to obtain

• a pure sample of solid copper hydroxide from the mixture

• a pure sample of solid sodium sulfate from the mixture.

Figure 9 shows the equipment used to electrolyse a sample of sodium sulfate solution.

Graphite electrodes are used in the electrolysis.

Give two reasons why graphite is a suitable material for the electrodes.

Sodium sulfate solution contains ions.

Which ions are attracted to the positive electrode during the electrolysis?

Draw one straight line from each electrode to the product formed at that electrode during the electrolysis of sodium sulfate solution.

Titration can be used to find the volume of dilute hydrochloric acid needed to neutralise 25.0 cm³ of barium hydroxide solution.

Before the titration is carried out, the pipette and conical flask are rinsed out with pure water.

Explain the effect, if any, that traces of water in the pipette and conical flask after rinsing could have on the titration result.

pipette

conical flask

In the titration, a few drops of phenolphthalein indicator are added to the barium hydroxide solution.

State the change in colour of phenolphthalein at the end point, when the barium hydroxide solution has just been neutralised.

Write the ionic equation for the neutralisation reaction that occurs when hydrochloric acid is added to barium hydroxide solution.

When barium hydroxide solution is neutralised by dilute sulfuric acid, a white precipitate of barium sulfate is formed in the conical flask.

Describe an experiment to obtain a sample of pure, dry barium sulfate from the contents of the conical flask.

When lead nitrate solution and potassium chloride solution are mixed, potassium nitrate and a precipitate of lead chloride are formed.

Complete the word equation for this reaction.

lead nitrate +_{........ ........} + lead chloride

Lead nitrate is toxic.

Which hazard symbol should be on a container of lead nitrate?

A student put 5 cm³ of potassium carbonate solution into a test tube and added 2 cm³ of calcium nitrate solution.

A precipitate formed and was allowed to settle as shown in Figure 7.

The height of the precipitate was measured.

Give the name of the piece of apparatus the student should use to find the volume of the potassium carbonate solution.

The student repeated the experiment.

The results are shown in Figure 8.

Use the data in Figure 8 to calculate the mean height of the precipitate.

Describe how a pure, dry sample of the precipitate could be obtained from the mixture in the test tube.

The student investigated whether increasing the volume of calcium nitrate solution increased the height of the precipitate formed.

They repeated the experiment using different volumes of calcium nitrate.

State one variable that should be controlled in this investigation.

Crystals of copper sulfate are prepared by reacting copper oxide, a base, with dilute sulfuric acid.

Name the other product of this reaction.

During the experiment, a spatula measure of copper oxide, a black powder, is added to warm, dilute sulfuric acid in a beaker.

When the mixture is stirred, the black powder disappears and the mixture turns pale blue.

The student then adds more copper oxide until the maximum amount of copper sulfate is formed without wasting copper oxide.

Explain how the student knows when to stop adding copper oxide.

The reaction produces an aqueous solution of copper sulfate.

What is the best way to obtain crystals of copper sulfate from an aqueous solution?

When some water is removed from the aqueous solution of copper sulfate, crystals of copper sulfate are made.

Describe how the arrangement and movement of the particles change as crystals are formed from a solution.

In this reaction, copper oxide, CuO, forms copper sulfate, CuSO₄.

Explain, in terms of electrons, whether the copper in copper oxide has been oxidised, has been reduced, or has not been oxidised or reduced.

In another experiment, a copper sulfate solution with a concentration of 39.875 g dm^–3 is used.

Calculate the mass of copper sulfate dissolved in 0.300 dm³ of this solution.

3.14 g of solid copper sulfate was dissolved in water and made up to 250 cm³ of solution.

Calculate the concentration of this copper sulfate solution in g dm⁻³.

concentration =_........ g dm

Sodium hydroxide solution was added to a solution of copper sulfate. A precipitate of copper hydroxide and a solution of sodium sulfate were formed.

State what would be seen in the reaction.

Complete the balanced equation for the reaction by adding a number in front of NaOH.

Describe how to obtain a pure, dry sample of the precipitate of copper hydroxide from the reaction mixture.

Figure 11 shows the ions in the sodium sulfate solution.

Draw a circle around each of the ions in Figure 11 that are attracted to the negative graphite electrode during the electrolysis.

State why it is important that the electrodes are inert.

Explain, in terms of its structure, how graphite conducts electricity.

A student carried out an investigation to determine the order of reactivity of four metals, W, X, Y and Z. A piece of metal W was added to a test tube containing excess dilute hydrochloric acid. This was repeated with the other three metals, X, Y and Z. In each case, the size of each piece of metal was the same. The student recorded observations on each reaction for three minutes.

The observations obtained are shown in Figure 8.

Use the information in Figure 8 to place the metals in order of reactivity from the least reactive to the most reactive.

The experiment was repeated using an excess of dilute sulfuric acid in place of the dilute hydrochloric acid.

metal + sulfuric acid metal sulfate + hydrogen

When metal Y reacts with dilute sulfuric acid, bubbles form quickly at first and then the reaction stops. Most of the solid metal remains.

Explain why the reaction between metal Y and excess dilute sulfuric acid stopped even though there was solid metal Y left.

The reactions between metals and dilute ethanoic acid are slower than reactions between metals and dilute hydrochloric acid. This is because ethanoic acid is a weak acid.

Explain the meaning of the term weak acid.

The formula of aluminium sulfate is Al₂(SO₄)₃.

Calculate the total number of atoms that combine to form 5.13 g of aluminium sulfate.

(relative atomic masses: O = 16.0, A l = 27.0, S = 32.0 Avogadro number = 6.0210²³)

number of atoms =_........

Iron is more reactive than lead. Iron reacts with lead nitrate solution to form solid lead. Two possible balanced equations for the reaction are

Equation 1 Fe + Pb(NO₃)₂ Fe(NO₃)₂ + Pb

Equation 2 2Fe + 3Pb(NO₃)₂ 2Fe(NO₃)₃ + 3Pb

In one experiment, it was found that 4.48 g of iron reacted with excess lead nitrate solution to form 24.84 g of lead.

Carry out a calculation, using the information above, to show which equation represents the reaction taking place.

(relative atomic masses: Fe = 56.0, Pb = 207)

Copper carbonate reacts with dilute nitric acid.

During the reaction the copper carbonate powder completely disappears.

State what can be deduced about the amount of acid used.

During the reaction, the pH of the mixture changed from 2 to 6.

By what factor has the concentration of the hydrogen ions in the mixture changed?

Using different reactants, a solution of copper sulfate was prepared.

Describe what should be done to obtain copper sulfate crystals from this copper sulfate solution.

When chloride ions are added to a pale blue solution containing copper ions, the mixture turns yellow.

This is a reversible reaction.

pale blue solution + chloride ions yellow solution + water

What effect does the removal of chloride ions have on the colour of the yellow mixture?

Hydrated copper sulfate has the formula CuSO₄.5H₂O. The formula tells us that each mole of copper sulfate contains 5 moles of water.

A sample of CuSO₄.5H₂O was heated gently until all the water was removed to form anhydrous copper sulfate, CuSO₄.

The mass of water formed was 4.5 g.

Calculate the mass of hydrated copper sulfate that was heated.

(relative atomic masses: H = 1.0, O = 16.0; relative formula mass: CuSO₄.5H₂O = 249.5)

mass of CuSO₄.5H₂O =_........

The word equation for the reaction between copper carbonate and dilute sulfuric acid is

copper sulfuric copper carbon

Complete the balanced equation for this reaction.

Calculate the relative formula mass of copper carbonate, CuCO₃. (relative atomic masses: C = 12.0, O = 16.0, Cu = 63.5)

relative formula mass of CuCO₃ =_........

What is the chemical test to show that a gas is carbon dioxide?

Figure 12 shows a conical flask containing dilute sulfuric acid. Copper carbonate is added to the acid in the flask. The copper carbonate is added one spatula measure at a time until the reaction has finished.

State two observations that would show the reaction has finished.

*(ii) Describe how you would obtain a solution of copper sulfate from the mixture and how you would obtain pure, dry copper sulfate crystals from this solution.

Your description should include the apparatus you would use.

You may wish to use diagrams in your answer.

Potassium hydroxide reacts with hydrochloric acid to form potassium chloride and water.

potassium hydroxide + hydrochloric acid potassium chloride + water

A student carried out a titration to find the exact volume of dilute hydrochloric acid that reacted with 25.0 cm³ of potassium hydroxide solution.

There were five steps in the titration. The steps shown are not in the correct order.

step J pour the potassium hydroxide solution into a conical flask and add a few drops of indicator to this solution step K fill a burette with the dilute hydrochloric acid and record the initial reading from the burette step L use a measuring cylinder to obtain 25 cm³ of potassium hydroxide solution step M take a final reading from the burette and calculate the volume of the dilute hydrochloric acid reacted step N run the dilute hydrochloric acid from the burette into the conical flask until the indicator changes colour

Write the steps in the correct order.

Some of the steps have been completed for you.

first step last step

Suggest an alternative piece of apparatus that could be used in step L to obtain exactly 25.0 cm³ of potassium hydroxide solution.

A student was then asked to produce a pure sample of solid potassium chloride.

After finding the volume of acid reacted in step M, the student added this volume of acid to a fresh 25.0 cm³ sample of the potassium hydroxide solution. This mixture was then evaporated.

Explain why this new mixture was evaporated rather than the original mixture from the titration, to produce a pure sample of solid potassium chloride.

After evaporation, the mass of the potassium chloride was determined.

The theoretical yield of the experiment was 0.70 g. The actual yield was 0.84 g.

This gave a percentage yield greater than 100%.

Calculate the percentage yield of this experiment.

percentage yield =_........

Suggest a reason why the actual yield was greater than the theoretical yield.

The equation for the reaction between potassium hydroxide solution and dilute hydrochloric acid is

Calculate the atom economy for the production of potassium chloride from potassium hydroxide and hydrochloric acid. (relative formula masses: KOH = 56.0, HCl = 36.5, KCl = 74.5, H₂O = 18.0)

Give your answer to one decimal place.

atom economy =_........

The word equation for the reaction between copper carbonate and dilute sulfuric acid is

copper sulfuric copper carbon

Complete the balanced equation for this reaction.

Calculate the relative formula mass of copper carbonate, CuCO₃. (relative atomic masses: C = 12.0, O = 16.0, Cu = 63.5)

relative formula mass of CuCO₃ =_........

What is the chemical test to show that a gas is carbon dioxide?

Figure 4 shows a conical flask containing dilute sulfuric acid. Copper carbonate is added to the acid in the flask. The copper carbonate is added one spatula measure at a time until the reaction has finished.

State two observations that would show the reaction has finished.

The electronic configuration of carbon is 2.4 The electronic configuration of oxygen is 2.6

Draw a dot and cross diagram for a molecule of carbon dioxide.

Show outer electrons only.

(a) Water, acidified with sulfuric acid, is decomposed by electrolysis. The water is decomposed to produce hydrogen and oxygen.

A sample of hydrogen is mixed with air and ignited.

State what would happen.

Throughout the experiment the volume of hydrogen and the volume of oxygen are measured at two-minute intervals.

The results are shown in Figure 2.

Describe, using the data in Figure 2, what the results show about the volumes of hydrogen and of oxygen produced in this experiment.

Molten lead bromide is electrolysed.

The products of this electrolysis are

Calcium nitrate and calcium carbonate are both ionic compounds.

Calcium nitrate mixed with water behaves as an electrolyte. Calcium carbonate mixed with water does not behave as an electrolyte.

Explain, in terms of solubility and movement of ions, this difference in behaviour.

When molten zinc chloride is electrolysed, zinc ions, Zn²⁺, form zinc atoms.

Write the half equation for this reaction.

Two compounds of barium are barium sulfide and barium chloride.

The hazard symbol shown in Figure 5 is on bottles containing barium metal.

State the meaning of this hazard symbol.

Give the names of the elements combined in barium sulfide.

Barium chloride is toxic.

Explain one safety precaution that should be taken when using barium chloride.

A beaker of barium chloride solution and a beaker of dilute sulfuric acid were placed on a balance, as shown in Figure 6.

The total mass reading on the balance was 25.7 g.

The dilute sulfuric acid was poured into the barium chloride solution and the beaker replaced on the balance, as shown in Figure 7.

Figure 7

The mixture formed contained a white precipitate.

State the total mass reading on the balance after the reaction.

Give the name of the white precipitate formed by the reaction of barium chloride solution with dilute sulfuric acid.

Solid sodium chloride is dissolved in water.

The sodium chloride solution is electrolysed in the apparatus shown in Figure 8.

State why sodium chloride solution, rather than solid sodium chloride, must be used in this experiment.

The formulae of the ions present in the sodium chloride solution are

Circle the ions that would be attracted to the anode.

Molten lead bromide can be electrolysed to form molten lead and bromine gas.

Explain how a student could modify the apparatus shown in Figure 8 to carry out this electrolysis.

State two characteristic properties of metals.

Acids are used to make salts.

Give the name of the acid used to make chlorides.

Salts of metals can be prepared by reacting the metal with an acid to produce the salt and hydrogen.

Describe the test to show that the gas is hydrogen.

Nickel is a metal.

Explain how the structure of a nickel atom, Ni, changes when it forms a nickel ion, Ni²⁺

A nickel sulfate solution is made by dissolving 23.5 g of nickel sulfate to make 250 cm³ of solution.

Calculate the concentration of the solution in g dm^–3.

concentration =_........ g dm

Excess solid nickel carbonate is added to dilute sulfuric acid in a beaker.

nickel sulfuric nickel carbon

Nickel sulfate is formed in solution.

Describe how a sample of pure, dry nickel sulfate crystals can be obtained from the mixture of nickel sulfate solution and excess solid nickel carbonate in the beaker.

(a) Salts of metals can be prepared by reacting the metal with an acid to produce the salt and hydrogen.

Describe the test to show the gas is hydrogen.

Nickel is a metal.

Explain how the structure of a nickel atom, Ni, changes when it forms a nickel ion, Ni²⁺.

A nickel sulfate solution is made by dissolving 23.5 g of nickel sulfate to make 250 cm³ of solution.

Calculate the concentration of the solution in g dm⁻³.

concentration =_........ g dm

Excess solid nickel carbonate is added to dilute sulfuric acid in a beaker.

nickel sulfuric nickel carbon

Nickel sulfate is formed in solution.

Describe how a sample of pure, dry nickel sulfate crystals can be obtained from the mixture of nickel sulfate solution and excess solid nickel carbonate in the beaker.