Concentration of solutions

Figure 8 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 8 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

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 7. The student measures the time taken for the cross to become visible. The experiment is repeated at different temperatures.

Figure 8 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 1. The student measures the time taken for the cross to become visible. The experiment is repeated at different temperatures.

Figure 2 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.

mass of solid Q =_........ g

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.

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^–3

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 6 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.

mass =_........ g

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⁻³

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.

_........ NaOH + CuSO₄ Cu(OH)₂ + Na₂SO₄

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

Figure 6 shows the equipment used to electrolyse a sample of sodium sulfate solution.

Graphite electrodes are used in the electrolysis of sodium sulfate solution. Graphite is used because it is inert and conducts electricity.

Figure 7 shows the ions in the sodium sulfate solution.

Draw a circle around each of the ions in Figure 7 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.

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⁻³

Dissolving ammonium chloride in water is an endothermic process. Figure 10 shows part of the reaction profile for this process.

Explain how Figure 10 shows that dissolving ammonium chloride in water is an endothermic process.

Complete the reaction profile in Figure 10 and label the activation energy.

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^–3

Dissolving ammonium chloride in water is an endothermic process. Figure 1 shows part of the reaction profile for this process.

Explain how Figure 1 shows that dissolving ammonium chloride in water is an endothermic process.

Complete the reaction profile in Figure 1 and label the activation energy.

Figure 6 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 6, 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 6 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 1 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

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^–3

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)

number of moles of copper sulfate =_........ mol

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)

mass =_........ g

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.

volume of solution =_........ cm³

State two characteristic properties of metals.

property 1_........

property 2_........

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