Identification of ions

Flame tests can be used to identify some metal ions.

Draw one straight line from each flame colour to the metal ion that produces that flame colour.

When potassium hydroxide solution is added to copper chloride solution, a precipitate of copper hydroxide and a solution of potassium chloride are formed.

Write the word equation for this reaction.

Copper hydroxide contains copper ions, Cu²⁺.

What colour is copper hydroxide?

The formula of potassium chloride is KC l.

Give the number of ions in the formula KC l.

A student carries out a flame test on a salt. The student observes a yellow flame.

Which ion is in the salt?

A molecule of a yellow substance is shown in Figure 1.

What is the formula of this molecule?

A bottle of this substance is labelled with the hazard symbol in Figure 2.

State the danger associated with the contents of this bottle.

Yellow bananas emit ethene gas, C₂H₄.

Draw one molecule of ethene, showing all covalent bonds.

Gold has a yellow colour.

A gold nanosphere has a surface area of 305 nm². The surface area to volume ratio is 1: 4.60.

Calculate the volume, in nm³, of the gold nanosphere.

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.

Compound A contains either aluminium ions or copper ions or iron(II) ions.

Figure 5 is a flow chart of the method for the test to identify the ions in compound A.

The precipitates formed in this test are solids.

Which state symbol is used for precipitates in equations?

A student is given a container of solid A and a bottle of dilute sodium hydroxide solution.

Describe how the student should carry out the test in Figure 5.

Include the names of the apparatus needed.

Iron(II) chloride is tested using the method in Figure 5.

State what would be seen when iron(II) chloride is tested.

What is the formula of an iron(II) ion?

A different compound is tested using the method in Figure 5.

When the sodium hydroxide solution is added, no precipitate forms.

State what can be concluded from this result.

In an experiment, the height of the precipitate formed in a reaction is measured using a 10 cm ruler.

The apparatus is shown in Figure 6.

Give the height of the precipitate in mm.

Figure 17 shows a poly(ethene) bottle containing substance K with one of its hazard symbols showing.

Explain a safety precaution that should be taken when using a substance with the hazard symbol shown in Figure 17.

Substance K has the formula AgNO₃. Give the name of substance K.

State one property of poly(ethene) that makes it a suitable material to make a container for storing substances.

A student tests a solid for chloride ions.

The student uses the following method.

step 1 dissolve a small amount of the solid in water

step 2 add some dilute hydrochloric acid

step 3 add a few drops of a solution of K

step 4 observe whether or not a white precipitate forms.

This method to show whether the solid contains chloride ions will not work.

Explain a change that needs to be made to step 2 to allow this method to work.

In the test for carbonate ions, the carbonate ions react with an acid.

Sodium carbonate, Na₂CO₃, is reacted with dilute hydrochloric acid.

Complete and balance the equation for this reaction.

Na₂CO₃ + 2HCl _........ +_........ +_........

The carbonate of element X has the formula X₂CO₃. The relative formula mass of this carbonate is 230.

Using this information, calculate the relative atomic mass of X.

(relative atomic masses: C = 12, O = 16)

Figure 6 shows a poly(ethene) bottle containing substance K with one of its hazard symbols showing.

Explain a safety precaution that should be taken when using a substance with the hazard symbol shown in Figure 6.

Substance K has the formula AgNO₃. Give the name of substance K.

State one property of poly(ethene) that makes it a suitable material to make a container for storing substances.

A student tests a solid for chloride ions.

The student uses the following method.

step 1 dissolve a small amount of the solid in water

step 2 add some dilute hydrochloric acid

step 3 add a few drops of a solution of K

step 4 observe whether or not a white precipitate forms.

This method to show whether the solid contains chloride ions will not work.

Explain a change that needs to be made to step 2 to allow this method to work.

In the test for carbonate ions, the carbonate ions react with an acid.

Sodium carbonate, Na₂CO₃, is reacted with dilute hydrochloric acid.

Complete and balance the equation for this reaction.

Na₂CO₃ + 2HCl _........ +_........ +_........

The carbonate of element X has the formula X₂CO₃. The relative formula mass of this carbonate is 230.

Using this information, calculate the relative atomic mass of X.

(relative atomic masses: C = 12, O = 16)

relative atomic mass of X =_........

A solid is known to be either aluminium chloride or aluminium sulfate or calcium chloride.

A few drops of sodium hydroxide solution are added to a solution of the solid and the mixture is shaken.

A white precipitate is seen.

A student concludes that the solid is aluminium sulfate.

Explain why this conclusion may not be correct.

Describe a test the student could use to confirm that the solid contains sulfate ions.

A solution containing iron ions is mixed with sodium hydroxide solution.

A green precipitate forms.

After a period of time exposed to air, the precipitate changes colour to brown.

Which statement would explain this change in colour?

*(c) A technician has samples of two substances, R and S.

R is an ionic solid.

Molecules of S contain 2 carbon atoms.

The technician carries out some tests on R and on a solution of S.

The tests and the results obtained are shown in Figure 11.

Identify R and S, using all of the data in Figure 11, explaining your reasoning from each test.

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.

Compounds are tested to see if they contain chloride, bromide or iodide ions.

Figure 5 shows a flow chart of this test.

Describe how to make a solution from a solid in a test tube.

Give the name of the apparatus that should be used to add a few drops of silver nitrate solution to the test tube.

When an equation is written for this reaction, which state symbol is used for the silver nitrate solution?

When one compound is tested, a precipitate is seen.

State what you see when a precipitate forms.

Using Figure 5, name the ion in the compound that causes a cream precipitate.

A compound of potassium is tested. It forms a white precipitate.

Using Figure 5, name the compound.

10.0 g of the solution of the compound of potassium are tested. 1.0 g of dilute nitric acid is added. 4 drops of silver nitrate solution are added, each with a mass of 0.2 g.

Calculate the mass of the mixture at the end of the test.

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.

A precipitate is produced when an alkaline solution is added to a solution containing some metal ions.

Which of these is evidence of a precipitate being produced?

You are given two solutions, one containing Ca²⁺ ions and the other containing Al³⁺ ions.

Devise a plan to identify which solution is which.

*(b) A scientist carries out some tests on solid V and on a solution of V.

The tests and results are shown in Figure 11.

Use the data in Figure 11 to deduce information about V, W and X, explaining your deductions.

A student carried out some tests on copper sulfate.

A flame test was carried out on some copper sulfate crystals.

The student used the following method.

step 1 dip a wire in hydrochloric acid, then hold the wire in a roaring Bunsen burner flame

step 2 dip the wire in hydrochloric acid again, then dip the wire in the copper sulfate crystals

step 3 hold the wire with the copper sulfate in the roaring Bunsen burner flame.

State why in step 1 the wire is dipped in hydrochloric acid and held in a roaring Bunsen burner flame.

State why in step 2 the wire is dipped in hydrochloric acid again before dipping it in the copper sulfate crystals.

What colour should be seen when the flame test is carried out on copper sulfate?

A solution of the copper sulfate was tested in a flame photometer.

Give an advantage of using a flame photometer, rather than a flame test, to test for copper ions.

Figure 7 shows some values obtained when producing a calibration graph for copper ions in a flame photometer.

Draw a line of best fit through the points.

A solution containing copper ions gave a display reading of 0.030.

Use the calibration graph in Figure 7 to find the concentration of copper ions in this solution.

concentration of copper ions =_........

The student tested an unknown solution for sulfate ions by

1. adding a few drops of dilute sulfuric acid to the unknown solution

2. then adding a few drops of barium chloride solution.

A white precipitate was formed.

The student cannot conclude from this result that the unknown solution contains sulfate ions.

Explain what the student should change to obtain a valid result.

Calculate the percentage by mass of copper in copper sulfate, CuSO₄.

(relative atomic masses: Cu = 63.5 relative formula mass of CuSO₄ = 159.5)

Give your answer to the nearest whole number.

percentage by mass of copper =_........

A technician was asked to find the concentration of potassium ions in a dilute solution using a flame photometer.

The technician first produced a calibration curve using solutions with known concentrations of potassium ions. Figure 9 contains the data for the calibration curve.

Use the information in Figure 9 to plot the calibration curve on the grid below.

The technician then obtained a reading of 360 for a dilute solution containing potassium ions.

Use the calibration curve to find the concentration of the potassium ions in this solution.

In the test for chloride ions, silver nitrate solution is added to a solution containing chloride ions. A white precipitate forms.

Write the ionic equation for this reaction.

*(c) A student was given a container of ammonium iron(II) sulfate, (NH₄)₂Fe(SO₄)₂. The student was also given a dilute solution of sodium hydroxide and access to other laboratory reagents.

Describe the tests the student should carry out to identify the ions in the ammonium iron(II) sulfate, including appropriate equations for the reactions involved.

Tests are carried out to identify the ions in two solids, P and Q.

A flame test is used to identify the metal ions in each of these solids.

Describe how to do a flame test.

Different metal ions produce different coloured flames.

Draw one straight line from each metal ion to its flame colour.

P and Q dissolve in water to form colourless solutions.

Figure 7 shows the results of tests on these solutions.

The anions in solutions of P and Q can be identified from the results of the tests shown in Figure 7.

Draw one straight line from each solution to the anion present.

The formula of barium chloride is BaCl₂.

Give the total number of ions in the formula BaCl₂.

A few drops of sodium hydroxide solution are added to a solution of iron(II) sulfate. Iron(II) hydroxide is formed.

State what would be seen.

One other product is formed in this reaction.

What is the name of this other product?

A chloride ion, a fluorine atom and a nanoparticle are all types of particle.

Which of the following shows the particles in order of size, starting from the smallest?

A solution, X, is thought to contain chloride, bromide or iodide ions.

The solution is tested to see whether it contains one of these ions. In the test, a few drops of two different solutions are added to X.

Name the two solutions that are added in the test.

The student carrying out the test records the following result.

Explain why the anion in X cannot be known for certain.

The metal ions in X could be identified using a flame test. There is a more sensitive and accurate instrumental method that can be used.

Give the name of an instrument that can be used to identify the metal ions in X.

Qualitative tests are carried out on ionic substances to identify the ions present in the substances.

The test for a given ion must be unique to that ion.

Explain why the test for a given ion must be unique to that ion.

In the test for the carbonate ion, CO₃^2–, dilute hydrochloric acid is added to the solid being tested.

State the name of the gas produced in the test if carbonate ions are present.

Tests for three ions are described.

Draw one straight line from the test for each ion to the observation that shows that ion to be present. Each observation may be correct for one test, more than one test, or for none of the tests.

description of test
observation

*(b) A white solid is known to be a chloride in which the metal ion is sodium, potassium, calcium or aluminium.

A chemist was told to carry out a test for each metal ion that could be present in this white solid.

Describe tests to show the presence of each of these metal ions.

A sample of potassium carbonate is contaminated with a small amount of sodium carbonate. When a flame test is carried out on the sample, a bright yellow flame is seen.

Describe how you could show that potassium and sodium ions are present in this sample.

Hydrochloric acid reacts with a solution of sodium carbonate.

Write the ionic equation for this reaction.

*(c) A student tests solutions of three ionic substances, K, L and M.

The student carries out the same two tests on each of the three solutions.

Test 1 add dilute nitric acid and then silver nitrate solution.

Test 2 add a few drops of sodium hydroxide solution and warm the mixture.

Figure 7 shows the results of the tests and the student’s conclusions about the identity of each substance.

None of the student’s conclusions are fully justified.

Explain which part of each conclusion is justified and what further work can be carried out to fully justify each conclusion.

Figure 3 shows two tests carried out on a white solid and the results of the tests.

Which ion is shown to be present by the result of test 1?

State the name of the gas given off in test 2.

State the name of the ion shown to be present in the white solid by the result of test 2.

A flame photometer can be used to measure the concentration of potassium ions in a solution.

Figure 4 shows the photometer readings for three different concentrations of potassium ions in solutions.

concentration of potassium ions in mg dm⁻³

Figure 4

A solution containing a concentration of potassium ions of 35 mg dm⁻³ is placed in the photometer. The photometer reading is 7.0.

Plot this point on the graph and then draw the straight line of best fit.

Another solution of potassium ions gives a photometer reading of 9.0.

Use the graph to find the concentration of potassium ions in this solution.

Qualitative tests are used to identify ions in compounds.

Solid X contains two ions.

The tests for these ions and their results are shown in Figure 10.

Use the information in Figure 10 to name the cation and the anion in solid X.

Another solid, Y, also contains two ions.

A test was carried out on solid Y.

A few drops of sodium hydroxide solution were added to a solution of solid Y. A white precipitate formed.

Give the reason why this test does not identify the cation in solid Y.

Give the reason why this test does not identify the anion in solid Y.

Instrumental methods are often used for analysis.

Give a reason why instrumental analysis may be better than other methods of analysis.

Iron(II) sulfate solution reacts with sodium hydroxide solution to form a pale green precipitate of iron(II) hydroxide, Fe(OH)₂.

Write the ionic equation for this reaction.

The green iron(II) hydroxide precipitate gradually turns brown when exposed to air.

Explain this observation.