The pH scale and neutralisation

A small piece of lithium is added to a trough of water.

State two observations made when lithium reacts with water.

What are the products of the reaction?

After the reaction is complete, a few drops of universal indicator are added to the solution in the trough.

Explain the colour and pH of the solution in the trough.

Give the formula of the ion responsible for this pH.

Lithium ions can be identified using a flame test.

What flame colour indicates the presence of lithium ions?

A teacher adds a small piece of lithium to water and collects the gas produced.

Give two observations when lithium is added to water.

The teacher adds a few drops of universal indicator to the solution at the end of the reaction.

Explain the final colour of the universal indicator.

This is the equation for the reaction between lithium and water.

The teacher collects 550 cm³ of hydrogen at rtp.

Calculate the mass, in grams, of lithium that the teacher added to the water.

[one mole of gas at rtp has a volume of 24 000 cm³]

[for lithium, A_r = 7]

[for carbon A_r = 12 for hydrogen, A_r = 1 for oxygen A_r = 16]

The teacher then adds a small piece of potassium to water.

Give one observation seen with potassium that is not seen with lithium.

Explain why potassium is more reactive than lithium.

Refer to atomic structure in your answer.

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 hydrogen chloride (HC l).

Hydrogen chloride is a covalent compound.

State, in terms of electrostatic attraction, what is meant by a covalent bond.

When hydrogen chloride gas is dissolved in an organic solvent, the hydrogen chloride remains a covalent molecule.

When hydrogen chloride gas is dissolved in water, ions are formed.

Explain what happens when dry blue litmus paper is dipped into separate samples of each solution.

In the presence of ultraviolet radiation, hydrogen reacts with chlorine to form hydrogen chloride.

This is the equation for the reaction.

The table shows the bond energies.

Calculate the enthalpy change (Δ H), in kJ/mol, for the reaction.

Include a sign in your answer.

ΔH =_........ kJ/mol

Draw a reaction profile for the reaction.

Label the reactants, the products, ΔH and the activation energy (E_a).

A technician needs to identify the solution in an unlabelled bottle.

The technician knows that the solution contains one of these compounds.

• iron(II) bromide

• iron(II) chloride

• iron(III) bromide

• iron(III) chloride

Describe how the technician can use chemical tests to identify the compound.

When chlorine gas is passed over heated iron powder, iron(III) chloride forms.

This is the equation for the reaction.

0.060 mol of chlorine gas is passed over 2.8 g of iron powder.

Show by calculation that the iron powder is in excess.

When iron(III) chloride dissolves in water, an acidic solution forms.

Give the colour of litmus in this solution.

Give the formula of the ion that causes the solution to be acidic.

The diagram shows two pieces of apparatus used in a titration.

Give the names of these pieces of apparatus.

Give the name of a suitable indicator that can be used in an acid-alkali titration.

A student does a titration using sodium carbonate solution and dilute nitric acid.

This is the equation for the reaction.

The table shows the concentrations of the two solutions and the volume of sodium carbonate used in the titration.

Use the equation and the data in the table to answer these questions.

Calculate the volume of dilute nitric acid that the student would need to neutralise the sodium carbonate solution.

Calculate the volume, in cm³, of carbon dioxide gas at rtp that would be produced from the 25.0 cm³ of the sodium carbonate solution.

[at rtp, molar volume = 24 000 cm³]

Describe a test to show that sodium carbonate solution contains carbonate ions.

This question is about oxygen.

Oxygen can be stored in tanks as a liquid or as a gas.

Complete the diagram to show the arrangement of six more particles in a gas.

Give a reason why a tank can store much more oxygen as a liquid.

Identify a hazard when storing oxygen as a gas.

Sulfur burns in oxygen to form sulfur dioxide.

Give one observation that can be made when sulfur burns in oxygen.

Some universal indicator is added to sulfur dioxide.

Explain the final colour of the universal indicator.

This question is about lithium and some of its compounds.

A small piece of lithium is added to a trough containing water.

The lithium floats on the surface of the water and a vigorous reaction occurs.

Give two other observations when lithium reacts with water.

A few drops of methyl orange are added to the solution in the trough.

Explain the final colour of the solution.

An unlabelled bottle containing a white powder is found in a laboratory.

Describe tests to show that the white powder in the bottle is lithium carbonate.

Lithium carbonate has ionic bonding.

State what is meant by the term ionic bonding.

A student does a titration to find the concentration of potassium hydroxide solution.

This is the student’s method.

• add 25.0 cm³ of the potassium hydroxide solution to a conical flask

• add a few drops of methyl orange indicator to the conical flask

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

• place the conical flask on a white tile

• add the acid from the burette to the mixture in the conical flask, swirling the flask continuously

• when the indicator changes colour at the end point, record the final burette reading

Repeat the titration to obtain concordant results.

Give the name of the most suitable piece of apparatus to measure out 25.0 cm³ of potassium hydroxide solution.

Give the colour of methyl orange in potassium hydroxide solution and in dilute sulfuric acid.

colour in potassium hydroxide solution

colour in dilute sulfuric acid

State why the student places the conical flask on a white tile.

State why the student swirls the flask continuously.

State what is meant by the term concordant results.

The student finds that 15.00 cm³ of sulfuric acid of concentration 0.180 mol / dm³ neutralises 25.0 cm³ of potassium hydroxide solution.

This is the equation for the reaction.

Calculate the concentration of the potassium hydroxide solution.

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

This is the ionic equation for the reaction between an acid and an alkali.

Explain why the OH⁻ ion is a proton acceptor in this reaction.

In this question the answer to each part is a number.

Give the pH value of a neutral solution.

Give a pH value of a weakly acidic solution.

Give the number of the Group in the Periodic Table that contains the elements that do not readily react.

Give the number of different elements present in glucose, C₆H₁₂O₆

A student is asked to find the concentration of a solution of nitric acid by doing a titration.

The student is provided with sodium hydroxide solution with a concentration of 0.350 mol/dm³

These are the first four steps in the student’s method.

• use a pipette to add exactly 25.0 cm³ of the nitric acid solution to a conical flask placed on a white tile

• add a few drops of indicator to the flask

• use a burette to add sodium hydroxide solution to the flask until the indicator has changed colour

• record the volume needed for the indicator to change colour

Give the reason for using the white tile.

Universal indicator is not a suitable indicator to use in a titration.

Complete the table to show the name of a suitable indicator and its final colour in this titration.

The student wants to obtain an accurate value for the volume of sodium hydroxide solution needed to neutralise the 25.0 cm³ of nitric acid.

Describe all the further steps the student should take.

This is a summary of the student’s results.

volume of HNO₃ used = 25.0 cm³

concentration of NaOH solution = 0.350 mol/dm³

volume of NaOH solution needed for neutralisation = 18.80 cm³

The equation for the reaction is

HNO₃ + NaOH NaNO₃ + H₂O

Calculate the amount, in moles, of NaOH that reacts.

Determine the amount, in moles, of HNO₃ that reacts.

amount of HNO₃ =_........

Calculate the concentration, in mol/dm³, of the HNO₃

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

The diagram shows the positions of some elements in part of the Periodic Table.

Na A l S C l

K Xe

Give the symbol of a metal from the diagram.

Give the symbol of an element from the diagram that forms an acidic oxide.

Give a similarity in the electron configurations of A l and I n.

Explain which element in the diagram is unreactive.

A teacher adds a small piece of sodium to a glass trough containing water and universal indicator.

The universal indicator changes colour.

The equation for the reaction is

Explain the final colour of the universal indicator.

The teacher repeats the experiment with potassium instead of sodium.

Give one similarity and one difference observed with potassium.

similarity

difference

The reaction with sodium produces 0.036 g of hydrogen gas.

One mole of hydrogen gas contains 6.010²³ molecules.

Calculate the number of molecules of hydrogen gas produced in the reaction with sodium.

Give your answer to two significant figures.

This question is about ammonia and ammonium compounds.

Ammonia (NH₃) is a simple covalent molecule.

Draw a dot-and-cross diagram to show the bonding in a molecule of ammonia.

The table shows the names and formulae of some ammonium compounds.

Complete the table by giving the missing information.

When ammonia reacts with sulfuric acid, ammonium sulfate is formed.

Write a chemical equation for this reaction.

Describe a test for ammonium ions.

The table gives some information about ammonia and ammonium compounds.

Calculate the percentage of nitrogen in ammonium nitrate.

[M_r of NH₄NO₃ = 80]

Fertilisers add nitrogen to the soil to help plants grow.

Ammonia and ammonium sulfate can both be used as fertilisers.

Discuss the advantages and disadvantages of using each of these compounds as fertilisers.

Use information from the table in your answer.

[pH of rainwater is approximately 5.6]

The diagram shows two pieces of apparatus, X and Y.

Give the name of each piece of apparatus.

In a titration, a student adds 25.0 cm³ of barium hydroxide solution to a conical flask.

Give a reason why it is better to use Y rather than X.

The student uses methyl orange indicator in the titration.

State the colour of methyl orange in barium hydroxide solution.

Give a reason why universal indicator is not suitable for use in a titration.

The student adds some dilute nitric acid to a burette and does the titration.

The equation for the reaction is

The student finds that 21.50 cm³ of nitric acid of concentration 0.600 mol/dm³ neutralises 25.0 cm³ of barium hydroxide solution.

Calculate the concentration, in mol/dm³, of the barium hydroxide solution.

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

State why sulfuric acid would not be a suitable acid to use in this titration.

A student does a titration to find the concentration of a solution of dilute sulfuric acid.

The student uses these solutions and this apparatus.

• dilute sulfuric acid

• potassium hydroxide solution of concentration 0.240 mol / dm³

• methyl orange indicator

The student wants to find the volume of sulfuric acid needed to neutralise 25.0 cm³ of the potassium hydroxide solution.

Describe how the student should do this titration.

Assume that all pieces of apparatus are clean and dry.

The student needs 15.00 cm³ of sulfuric acid to neutralise 25.0 cm³ of the potassium hydroxide solution.

This is the equation for the reaction.

Calculate the amount, in moles, of KOH in 25.0 cm³ of potassium hydroxide solution of concentration 0.240 mol / dm³.

Calculate the amount, in moles, of H₂SO₄ in 15.00 cm³ of the sulfuric acid.

amount of H₂SO₄ =_........

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

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

This question is about the reactions of Group 1 metals with water.

A teacher adds a piece of sodium to some water containing universal indicator.

The equation for this reaction is

The sodium floats on the surface of the water and the universal indicator changes colour because an alkaline solution is formed.

Give two other observations.

Give the final colour of the universal indicator.

The diagram represents an atom of lithium and an atom of sodium.

Give a reason why lithium and sodium have similar reactions with water.

Explain why lithium is less reactive than sodium.

The teacher adds 0.150 g of lithium to an excess of water and collects the hydrogen gas produced.

The equation for the reaction is

The teacher collects 254 cm³ of hydrogen gas at room temperature and pressure (rtp).

Show by calculation that 1 mol of hydrogen gas has a volume of approximately 24 000 cm³ at rtp.

This question is about ionic compounds.

State the formula of the cation and the anion in magnesium sulfate.

The diagram shows the electronic configuration of a potassium atom and an oxygen atom.

Potassium oxide (K₂O) is an ionic compound.

Draw the electronic configuration of a potassium ion and an oxide ion.

Show the charge on each ion.

A sample of solid potassium oxide is added to water.

A reaction occurs and a colourless solution forms.

When a few drops of phenolphthalein indicator are added to the solution it turns pink.

Identify the ion responsible for the colour change.

Give a chemical equation for the reaction between potassium oxide and water.

Explain why ionic compounds conduct electricity when molten or in aqueous solution, but not when in the solid state.

The diagram shows the apparatus a teacher uses to demonstrate the electrolysis of a concentrated aqueous solution of sodium chloride.

During the electrolysis two gases, X and Y, are formed. One of the gases produces a squeaky pop when tested with a lighted splint.

Use ionic half‑equations to identify X and Y.

This question is about sodium and potassium.

A trough is filled with water and a few drops of phenolphthalein indicator are added.

A small piece of sodium is dropped into the water. One of the products of the reaction is an alkali.

Complete the chemical equation for the reaction of sodium with water.

_____Na(_........ ) + ______H₂O(l) _____NaOH(_........ ) + H₂(g)

Identify the ion that causes the solution to become alkaline.

Give three observations that would be made when sodium reacts with water.

Explain why potassium is more reactive than sodium.

Refer to the electronic configurations of the atoms in your answer.

A student does a titration using dilute sulfuric acid to find the concentration of a solution of potassium hydroxide.

The student adds 25.0 cm³ of the potassium hydroxide solution to a conical flask. He then adds a few drops of methyl orange indicator.

The student does the titration four times.

Name the piece of apparatus the student should use to add the potassium hydroxide solution.

What is the colour of methyl orange in an alkaline solution?

The table shows the student’s results.

Concordant results are those within 0.20 cm³ of each other.

Place ticks (✓) in the table to show which results are concordant.

Use the concordant results to calculate the mean (average) volume of acid added.

This table shows the student’s results for another titration.

The equation for the reaction is

Calculate the amount, in moles, of KOH in 25.0 cm³ of the potassium hydroxide solution.

Calculate the amount, in moles, of H₂SO₄ in 21.20 cm³ of sulfuric acid.

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

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

Sodium hydroxide dissolves in water, forming a strongly alkaline solution.

Ammonia dissolves in water, forming a slightly less alkaline solution.

Identify the ion that makes the sodium hydroxide solution alkaline.

What is a possible pH of ammonia solution?

When ammonia solution reacts with sulfuric acid, a neutralisation reaction occurs and ammonium sulfate forms.

How does the sulfuric acid act in this reaction?

The diagram shows a beaker containing some ammonia solution and a few drops of phenolphthalein indicator.

Dilute sulfuric acid is added to the beaker until it is in excess.

What are the colours of the phenolphthalein indicator before and after adding excess sulfuric acid?

Ammonium sulfate is used by gardeners as a fertiliser because it contains nitrogen.

Explain why the chemical formula of ammonium sulfate is (NH₄)₂SO₄

Refer to the charges on the ions in your answer.

Calculate the relative formula mass of ammonium sulfate, (NH₄)₂SO₄

Calculate the mass, in grams, of nitrogen in 1.0 kg of ammonium sulfate.

This question is about some compounds of the elements in Group 4 of the Periodic Table.

When carbon dioxide dissolves in water, a weak acid forms.

Which of these could be the pH of this weak acid?

Which of these is a correct statement about acids?

When lead(II) carbonate is heated, lead(II) oxide and carbon dioxide form.

Give the name of this type of reaction.

Complete the equation for this reaction.

Silicon dioxide, SiO₂, and silicon(IV) chloride, SiCl₄, are both covalently bonded compounds.

The table shows the melting and boiling points of these two compounds, and the physical state of silicon dioxide at room temperature.

Complete the table by giving the physical state of silicon(IV) chloride at room temperature.

Explain, in terms of structure and bonding, why silicon dioxide has a much higher melting point than silicon(IV) chloride.

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

A student is provided with a bottle containing a colourless solution X.

Solution X is thought to be dilute sulfuric acid of concentration 0.10 mol/dm³.

The student does some experiments on samples of solution X to try to show that it is dilute sulfuric acid.

The student adds a few drops of litmus to a sample of solution X.

The litmus turns red.

The student knows that the products of the electrolysis of dilute sulfuric acid are hydrogen and oxygen.

She carries out the electrolysis using this apparatus.

Suggest why the student does not use zinc electrodes in her experiment.

State what is observed at both the anode and the cathode during the electrolysis.

Which of these tests shows that the gas formed at the cathode is hydrogen?

Describe a test to show that solution X contains sulfate ions.

The student then does a titration to see if the concentration of the dilute sulfuric acid is 0.10 mol/dm³.

She measures 25.0 cm³ of potassium hydroxide solution into a conical flask, and then adds a few drops of indicator solution.

Name the piece of apparatus the student should use to measure 25.0 cm³ of the potassium hydroxide solution.

The concentration of potassium hydroxide in the solution is 0.125 mol/dm³.

Calculate the amount, in mol, of KOH in 25.0 cm³ of this solution.

The equation for the reaction in the titration is

Calculate the volume, in cm³, of 0.10 mol/dm³ sulfuric acid needed to neutralise 25.0 cm³ of the potassium hydroxide solution.

A student investigates the reaction between sodium hydroxide solution and hydrochloric acid.

He uses this method.

Step 1 add 50 cm³ of dilute hydrochloric acid to a conical flask

Step 2 add a 5 cm³ portion of sodium hydroxide solution to the conical flask

Step 3 test the pH of the mixture using both universal indicator paper and a pH meter

The student repeats step 2 and step 3 until a total of 50 cm³ of sodium hydroxide solution has been added.

State the piece of apparatus that should be used to measure 50 cm³ of hydrochloric acid.

Name the type of reaction that occurs between hydrochloric acid and sodium hydroxide.

Graph 1 shows how the pH of the mixture changes as the sodium hydroxide solution is added.

Volume of sodium hydroxide solution in cm³

Graph 1

Determine the pH after 40 cm³ of sodium hydroxide solution has been added.

Suggest the colour of the universal indicator paper when these volumes of sodium hydroxide solution have been added.

Give the formula of the ion that causes sodium hydroxide to be alkaline.

Another student investigates how the temperature changes when the sodium hydroxide solution is added to the hydrochloric acid.

The hydrochloric acid and the sodium hydroxide solution are at the same temperature at the start of the investigation.

The student records the temperature of the mixture after adding each 5 cm³ portion of sodium hydroxide solution.

Graph 2 shows her results.

Volume of sodium hydroxide solution in cm³

Graph 2

Explain the shape of graph 2.

A student investigates the reaction between sodium hydroxide solution and dilute sulfuric acid.

He does a titration to find the concentration of the sulfuric acid.

This is his plan for the titration. There are some mistakes and omissions in his plan.

● rinse a conical flask with the sodium hydroxide solution

● use a measuring cylinder to measure out 25 cm³ of the sodium hydroxide solution and add it to the conical flask

● add a few drops of methyl orange indicator to the conical flask

● rinse a burette with water and then fill it with the sulfuric acid

● add the acid from the burette to the conical flask until the indicator changes colour at the end‑point of the titration

● record the final burette reading

Give the colour change of the methyl orange indicator at the end‑point.

Describe four changes that the student could make to improve his plan.

The student then does the titration correctly.

He finds that 16.70 cm³ of the dilute sulfuric acid neutralises 25.0 cm³ of sodium hydroxide solution of concentration 0.200 mol/dm³

The equation for the reaction is

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

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

When a bottle of wine is left open for several days, some of the ethanol in the wine turns to ethanoic acid, CH₃COOH

A scientist uses a titration method to investigate how much ethanoic acid is formed if a bottle of white wine is left open for one week.

She uses this method.

● fill a burette with the white wine and record the reading

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

● add a few drops of phenolphthalein indicator to the flask

● swirl the flask continuously while adding wine from the burette

● add the wine drop by drop near the end point

● record the reading at the end point

Name the piece of apparatus that would be most suitable for measuring the 25.0 cm³ of sodium hydroxide solution.

Suggest why red wine would not be suitable to use for this investigation.

State why she swirls the flask continuously.

State why she adds the wine drop by drop near the end point.

The diagram shows the burette readings at the start and end of one of the titrations.

Use the readings to complete the table.

Give your values to the nearest 0.05 cm³.

The scientist repeats the titration four more times.

The table shows her results for these four titrations.

Concordant results are those within 0.20 cm³ of each other.

Add ticks () to the table to show the concordant results.

Use your ticked results to calculate the mean (average) volume of wine added.

Another scientist repeats the titration with a different bottle of white wine that has been left open for a week.

The equation for the reaction that occurs in this titration is

CH₃COOH + NaOH CH₃COONa + H₂O

The mean volume of wine added is 19.50 cm³.

The concentration of the sodium hydroxide solution is 0.0500 mol/dm³.

Calculate the amount, in moles, of NaOH in 25.0 cm³ of sodium hydroxide solution.

Deduce the amount, in moles, of CH₃COOH in 19.50 cm³ of the wine.

Calculate the concentration, in mol/dm³, of CH₃COOH in the wine.

concentration of CH₃COOH =_........ mol/dm³