Concentration of solutions

Figure 11 shows part of the reactivity series of metals.

The method used to extract a metal from its ore is related to the metal’s position in the reactivity series.

Which metal is found in the Earth’s crust as an uncombined element?

Name one metal in Figure 11 that is normally extracted by electrolysis.

25 000 kg of an ore of iron was found to contain 10 050 kg of iron.

Calculate the percentage of iron in this ore of iron.

percentage of iron in ore =_........

When copper oxide is heated with carbon, the products are copper and carbon dioxide.

Write the word equation for this reaction.

In this reaction, copper oxide loses oxygen.

State the type of reaction when copper oxide loses oxygen.

In one reaction, 159.0 g of copper oxide was heated with excess carbon to produce 127.0 g of copper.

Use this information to calculate the mass of copper formed, in g, when 238.5 g of copper oxide is reacted with excess carbon.

mass of copper =_........ g

State why this reaction with copper oxide uses excess carbon.

A solution of zinc sulfate was made by dissolving 23.8 g of the compound in water and was made up to a total volume of 250 cm³ with water.

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

Give your answer to 2 significant figures.

concentration =_........ g dm^–3

A student is asked to carry out a titration to find the concentration of a sodium hydroxide solution.

A teacher dilutes some sulfuric acid with distilled water to make a solution with a concentration of 0.250 mol dm^–3 for the student to use.

What effect does diluting the sulfuric acid with distilled water have on the pH of the solution and the concentration of the H⁺ ions?

What is the concentration, in g dm^–3, of a 0.250 mol dm^–3 solution of H₂SO₄?

(relative formula mass: H₂SO₄ = 98.0)

The student uses the apparatus shown in Figure 10 to carry out the titration.

Before using the apparatus, the student rinses the burette with distilled water.

This is an error.

Explain what effect this error has on the result of the titration.

State what the student should do to correct the error.

*(c) The equation for the reaction in the titration is

Explain how the equation for the reaction and the apparatus in Figure 10 can be used to find the concentration of 25.0 cm³ of sodium hydroxide solution using the 0.250 mol dm^–3 sulfuric acid.

When solutions P and Q are mixed together, a purple mixture forms. This mixture slowly becomes colourless.

A student pours 25 cm³ of solution P into a conical flask and then adds 25 cm³ of solution Q.

The student uses a beaker to measure out these volumes.

Name a piece of apparatus that could be used to measure these volumes more accurately.

The student investigates this reaction using the apparatus shown in Figure 12. The student measures the time taken for the cross to become visible. The experiment is repeated at different temperatures.

Figure 13 shows the results.

The concentrations of the solutions are kept constant in each experiment.

State one other variable that should be kept constant.

State, and explain in terms of particles, how the time taken for the cross to become visible would change if a temperature of 80 °C was used.

The concentration of solution Q is 26.8 g dm^–3.

Calculate the mass of solid Q present in 25 cm³ of solution Q.

The student repeats the experiment at 20 °C, with the addition of a catalyst.

Explain how the addition of a catalyst will affect the rate of reaction.

Hydrogen peroxide, H₂O₂, decomposes into oxygen and water.

A catalyst can be used to increase the rate of this reaction.

Use a word or phrase from the box to complete the sentence about the mass of the catalyst in a reaction.

During a reaction, the mass of a catalyst_........ .

Complete the balanced equation for this reaction and add the missing state symbol.

When solutions P and Q are mixed together, a purple mixture forms. This mixture slowly becomes colourless.

A student pours 25 cm³ of solution P into a conical flask and then adds 25 cm³ of solution Q.

The student uses a beaker to measure out these volumes.

Name a piece of apparatus that could be used to measure these volumes more accurately.

The student investigates this reaction using the apparatus shown in Figure 3. The student measures the time taken for the cross to become visible. The experiment is repeated at different temperatures.

Figure 4 shows the results.

The concentrations of the solutions are kept constant in each experiment.

State one other variable that should be kept constant.

State, and explain in terms of particles, how the time taken for the cross to become visible would change if a temperature of 80 °C was used.

The concentration of solution Q is 26.8 g dm^–3.

Calculate the mass of solid Q present in 25 cm³ of solution Q.

The student repeats the experiment at 20 °C, with the addition of a catalyst.

Explain how the addition of a catalyst will affect the rate of reaction.

Figure 12 shows the calibration graph of a flame photometer for the concentration of calcium ions in a solution.

concentration of calcium ions in mg dm^–3

Figure 12

Use Figure 12 to find the concentration of calcium ions when the photometer reading is 175.

A flame photometer was used to measure the concentration of sodium ions in tap water and three types of bottled water.

The results are shown in Figure 13.

Calculate the mean concentration of sodium ions in the three bottled waters.

mean concentration =_........ mg dm

Calculate the volume of tap water, in dm³, that contains 3 moles of sodium ions.

(relative atomic mass: Na = 23)

A student is given two test tubes, one containing solid aluminium chloride and the other containing solid calcium chloride.

Describe the test the student should use to show which solid is in which test tube, giving the observation for each compound.

Silver carbonate and silver bromide are both insoluble solids.

A student tests a solution to see if it contains bromide ions. The student adds a few drops of silver nitrate solution. A precipitate forms.

The student repeats the test but adds some dilute nitric acid before adding the silver nitrate solution. The mixture fizzes and no precipitate forms.

Explain what conclusion the student can draw from these results.

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.

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.

A student carried out a flame test on a sample of solid potassium chloride.

The student followed this method.

step 1 dip a dry wooden splint into water

step 2 then dip the wooden splint into the sample of potassium chloride

step 3 hold the wooden splint in a roaring Bunsen burner flame

step 4 observe the colour seen in the flame.

The student made the following observation and conclusion.

‘ I saw that the flame colour was yellow so the sample must contain sodium ions.’

Due to the way the student carried out the experiment, this is not a valid conclusion.

Explain one improvement that the student could make to their method to obtain a valid conclusion.

improvement

reason

What colour should the student have seen in the flame if the test had been carried out correctly?

A sample of the potassium chloride was also tested for chloride ions.

Describe the test for chloride ions.

A student was asked to test a sample of aluminium sulfate for sulfate ions.

The student needed 25 cm³ of barium chloride solution of concentration

Calculate the mass of barium chloride that must be dissolved in water to make 25 cm³ of solution of this concentration.

Give your answer to 2 significant figures.

When the barium chloride solution was added to the aluminium sulfate solution, a precipitate was formed.

The balanced equation for this reaction is

Write the ionic equation for this reaction.

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.

Some acids are used in tests for ions.

A bottle of one acid is shown in Figure 17.

The acid in Figure 17 can be used in the test for carbonate ions.

Explain, giving the name of the hazard symbol shown, what safety precautions should be taken when using this acid.

Give the name of the acid shown in Figure 17.

State a property of glass that makes it a suitable material to make the container for an acid.

A teacher conducts a flame test to identify the metal ions in some unknown solids.

step 1 dip a flame test wire into hydrochloric acid

step 2 dip the flame test wire into the unknown solid

step 3 hold the flame test wire above a Bunsen burner flame

This method did not work well.

Explain an improvement that needs to be made to step 3 to enable a bright flame colour to be produced.

Figure 18 shows the results of the flame tests on three compounds, P, Q and R.

Use Figure 18 to identify the metal ions in compounds P, Q and R.

A flame photometer was used to analyse samples of a solution of metal ions.

Each sample was treated with 5.00 cm³ of dilute hydrochloric acid. 1.00 dm³ of the acid contained 219 g of hydrogen chloride.

Calculate the mass of hydrogen chloride in the acid used to test 20 samples.

Some acids are used in tests for ions.

A bottle of one acid is shown in Figure 6.

The acid in Figure 6 can be used in the test for carbonate ions.

Explain, giving the name of the hazard symbol shown, what safety precautions should be taken when using this acid.

Give the name of the acid shown in Figure 6.

State a property of glass that makes it a suitable material to make the container for an acid.

A teacher conducts a flame test to identify the metal ions in some unknown solids.

step 1 dip a flame test wire into hydrochloric acid

step 2 dip the flame test wire into the unknown solid

step 3 hold the flame test wire above a Bunsen burner flame

This method did not work well.

Explain an improvement that needs to be made to step 3 to enable a bright flame colour to be produced.

Figure 7 shows the results of the flame tests on three compounds, P, Q and R.

Use Figure 7 to identify the metal ions in compounds P, Q and R.

A flame photometer was used to analyse samples of a solution of metal ions.

Each sample was treated with 5.00 cm³ of dilute hydrochloric acid. 1.00 dm³ of the acid contained 219 g of hydrogen chloride.

Calculate the mass of hydrogen chloride in the acid used to test 20 samples.

If liquid water is cooled below 0 °C it turns into the solid, ice.

Give the name for the change of state from liquid to solid.

Here are five statements about ice and water.

Place ticks in boxes by the two statements that are correct.

Figure 2 shows a label from a bottle of drinking water.

Explain why this drinking water should not be described as pure water.

State the information from Figure 2 that shows that the drinking water is neutral.

Calculate the mass of calcium ions in 250 cm³ of this drinking water.

State how you know that calcium is a metal from its position in the periodic table.

A sample of solid potassium hydroxide contained soluble, unreactive impurities.

A student tried to find the mass of potassium hydroxide in the sample, using the following method.

step 1 measure the mass of the sample of impure potassium hydroxide

step 2dissolve the sample in 250 cm³ of water in a beaker

step 3take a 25 cm³ sample of the potassium hydroxide solution using a measuring cylinder and pour into a conical flask

step 4 add 3 drops of indicator to the solution

step 5 put the conical flask on a white tile

step 6 using a burette, add dilute sulfuric acid of known concentration drop by drop to the solution, while swirling the flask

step 7 continue adding the sulfuric acid until the colour of the solution changes

step 8 record the volume of sulfuric acid added

step 9 use this result to calculate the mass of pure potassium hydroxide in the sample.

Suggest three ways to improve this method to obtain a more accurate mass of pure potassium hydroxide.

The indicator used was phenolphthalein.

Which row shows the colour change that would be seen in this titration?

Another student carried out the titration accurately.

12.15 cm³ of dilute sulfuric acid with a concentration of 0.140 mol dm^–3 reacted completely with 25.00 cm³ of potassium hydroxide solution.

Calculate the concentration of this potassium hydroxide solution.

concentration of potassium hydroxide solution =_........ mol dm

A different solution of potassium hydroxide had a concentration of 0.175 mol dm^–3.

This potassium hydroxide solution was made by dissolving 2.56 g of impure potassium hydroxide to form 250 cm³ of solution.

Calculate the percentage by mass of potassium hydroxide in the impure potassium hydroxide.

(relative formula mass: KOH = 56.0)

percentage by mass of potassium hydroxide =_........

The concentration of a solution can be calculated using the equation

A student dissolved 9.25 g of ammonium chloride in water and made up the

Use the equation to calculate the concentration of this solution in gdm⁻³.

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

Dissolving ammonium chloride in water is an endothermic process. Figure 17 shows part of the reaction profile for this process.

Explain how Figure 17 shows that dissolving ammonium chloride in water is an endothermic process.

Complete the reaction profile in Figure 17 and label the activation energy.

A student used the equipment in Figure 18 to investigate whether electricity can pass through solid ammonium chloride and through ammonium chloride solution.

If an electrical current flows in the circuit, the lamp will light up.

Figure 19 shows the results of the investigation.

Explain the results of the investigation.

Ammonia gas is toxic.

Which symbol should be placed on a container of a toxic gas?

Give one safety precaution that should be taken when working with toxic gases in the laboratory.

The concentration of a solution can be calculated using the equation

A student dissolved 9.25 g of ammonium chloride in water and made up the

Use the equation to calculate the concentration of this solution in gdm⁻³.

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

Dissolving ammonium chloride in water is an endothermic process. Figure 2 shows part of the reaction profile for this process.

Explain how Figure 2 shows that dissolving ammonium chloride in water is an endothermic process.

Complete the reaction profile in Figure 2 and label the activation energy.

A student used the equipment in Figure 3 to investigate whether electricity can pass through solid ammonium chloride and through ammonium chloride solution.

If an electrical current flows in the circuit, the lamp will light up.

Figure 4 shows the results of the investigation.

Explain the results of the investigation.

Figure 11 shows the apparatus that can be used to electrolyse sodium sulfate solution using inert electrodes.

Hydrogen is produced at the negative electrode during electrolysis.

Describe the test to show the gas is hydrogen.

What is the name of gas X that forms at the positive electrode?

State what is meant by the term electrolysis.

The sodium sulfate solution was made by dissolving 28.4 g of sodium sulfate in water to make 250 cm³ of solution.

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

Give your answer to three significant figures.

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

The ions present in sodium sulfate are

Write the formula of sodium sulfate using this information.

In Figure 11, the gases given off at the electrodes are collected in test-tubes. However, the actual volume of gases cannot be measured using these test-tubes.

Suggest what apparatus could be used in place of the test-tubes in Figure 11 to measure the volume of gases given off.

State what could be added into the circuit to show a current is flowing during electrolysis.

Figure 3 shows the apparatus that can be used to electrolyse sodium sulfate solution using inert electrodes.

Hydrogen is produced at the negative electrode during electrolysis.

Describe the test to show the gas is hydrogen.

What is the name of gas X that forms at the positive electrode?

State what is meant by the term electrolysis.

The sodium sulfate solution was made by dissolving 28.4 g of sodium sulfate in water to make 250 cm³ of solution.

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

Give your answer to three significant figures.

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

The ions present in sodium sulfate are

Write the formula of sodium sulfate using this information.

Sodium thiosulfate solution, Na₂S₂O₃, reacts with dilute hydrochloric acid.

When dilute hydrochloric acid is mixed with sodium thiosulfate solution, the mixture turns cloudy.

Explain why the mixture turns cloudy.

In an investigation, different concentrations of hydrochloric acid are reacted with sodium thiosulfate solution. The mixture goes cloudy at different rates.

Describe how the rate at which the mixture goes cloudy can be measured.

You are provided with some dilute hydrochloric acid which has a concentration of 50 g dm^–3.

For this experiment, dilute hydrochloric acid with a concentration of 20 g dm^–3 is required.

How much water must be added to 100 cm³ of 50 g dm^–3 hydrochloric acid to make dilute hydrochloric acid with a concentration of 20 g dm^–3?

Sodium iodide solution is colourless.

When a solution of bromine is added to sodium iodide solution, a reaction occurs.

The mixture turns brown.

Give the name of the substance causing the brown colour.

Explain which substance has been reduced in this reaction.

The first four elements in group 1 are lithium, sodium, potassium and rubidium.

Rubidium reacts with water to form rubidium hydroxide and hydrogen.

Predict what you would see when a small piece of rubidium is placed in a large volume of water.

Why is rubidium more reactive than potassium?

8.5 g of rubidium are reacted completely with water.

The reaction makes a solution of rubidium hydroxide. The volume of this solution is 2.5 dm³.

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

(relative atomic mass: Rb = 85; relative formula mass: RbOH = 102)

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

An example of an endothermic reaction is the reaction between rubidium hydroxide and ammonium carbonate, (NH₄)₂CO₃.

This reaction forms rubidium carbonate, Rb₂CO₃, ammonia and one other product.

Write the balanced equation for this reaction.

Pieces of zinc react with copper sulfate solution. Zinc sulfate solution is colourless.

Describe what you would see when an excess of zinc is added to copper sulfate solution and the mixture left until the reaction is complete.

This reaction is described as a redox reaction.

Explain, in terms of electrons, which particles have been oxidised and which particles have been reduced in this reaction.

The copper sulfate solution used has a concentration of 15.95 g dm⁻³.

Calculate the number of moles of copper sulfate, CuSO₄, in 50.00 cm³ of this solution. (relative atomic masses: O = 16, S = 32, Cu = 63.5)

In another experiment, 0.043 mol of copper sulfate, CuSO₄, is used.

Calculate, to one decimal place, the minimum mass of zinc that must be added to react with all the copper sulfate. (relative atomic mass: Zn = 65)

A student poured 50 cm³ water into a beaker and measured the water’s temperature.

The student added 1.00 g calcium chloride to the water, stirred the mixture and then recorded the temperature.

Give the name of the apparatus that could be used to measure 1.00 g of calcium chloride.

The student’s results were

temperature of water at start = 21C temperature of mixture after stirring = 32C

Explain, using these results, the type of heat energy change that occurs when calcium chloride dissolves in water.

Calcium chloride is hazardous to health.

Which hazard symbol would be expected to be seen on a container of calcium chloride?

Give a safety precaution that the student should take during the experiment.

State one way in which the apparatus could be changed to reduce the amount of heat energy lost during the experiment.

The concentration of a calcium chloride solution is 12 g dm^–3.

Calculate the volume of this solution, in cm³, that contains 9.0 g of calcium chloride.

You must show your working.

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.

The concentration of dilute sulfuric acid can be determined by titration with sodium hydroxide solution of known concentration.

25.00 cm³ of dilute sulfuric acid was measured out using a pipette and transferred to a conical flask. A few drops of methyl orange indicator were added to the acid in the conical flask. Sodium hydroxide solution was added to the acid from a burette until the indicator changed colour. The titration was repeated until two concordant results were obtained. The accurate result was the average of the two concordant results.

Describe the colour change seen at the end point of the titration.

A brief report of the practical method has been given above. Further detail can be added to this method to ensure that anyone following the method will obtain an accurate result.

Explain two details that could be added to this practical method to ensure an accurate result is obtained.

In the titration, 25.00 cm³ of dilute sulfuric acid reacted with 24.25 cm³ of 0.200 mol dm⁻³ sodium hydroxide solution, NaOH.

Calculate the concentration of the dilute sulfuric acid, H₂SO₄, in mol dm⁻³.

concentration of sulfuric acid =_........ mol dm

The concentration of some dilute sulfuric acid, H₂SO₄, is 0.250 mol dm⁻³.

Calculate the concentration of sulfuric acid in this solution in g dm⁻³. (relative formula mass: H₂SO₄ = 98)

concentration of sulfuric acid =_........ g dm