The pH scale & neutralisation

A student makes some ammonium sulfate solution by using a titration.

Which pair of solutions should be used to make the ammonium sulfate solution?

The student uses the following apparatus to make the solution of ammonium sulfate.

Draw one straight line from each apparatus name to the diagram of the apparatus.

In this titration, the student uses methyl orange as the indicator.

Explain why an indicator is used in a titration.

The student carries out a rough titration first.

Figure 9 shows the burette readings at the start and at the end of the titration.

At the start of the titration, the burette reading is 2.15 cm³.

Give the reading on the burette at the end of the titration.

The student carries out accurate titrations to obtain concordant results.

Figure 10 shows the volume of solution delivered by the burette in the three accurate titrations.

Circle the volumes the student should use to calculate the mean volume.

Using the volumes that you have circled, calculate the mean volume of solution delivered by the burette.

mean volume of solution =_........ cm³

Phosphoric acid is important in the production of fertilisers.

A few drops of litmus solution are added to a sample of dilute phosphoric acid.

What is the colour of the mixture formed?

State why litmus cannot be used to measure pH.

Phosphoric acid can react to form phosphate salts which are used in fertilisers.

Give two reasons why farmers use fertilisers on their fields.

An experiment was carried out to produce phosphoric acid.

The actual yield for the experiment was 18.62 g.

The theoretical yield for the experiment is 24.50 g.

Calculate the percentage yield of this experiment.

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

The equation for a reaction to make phosphoric acid, H₃PO₄, is

Calculate the atom economy for the production of phosphoric acid in this reaction.

(relative formula masses: Ca₅(PO₄)₃OH = 502, H₂SO₄ = 98, H₃PO₄ = 98, CaSO₄ = 136, H₂O = 18)

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

The equation for a reaction to produce phosphoric acid is

Explain how the atom economy of the reaction can be increased.

Phosphoric acid is important in the production of fertilisers.

A few drops of litmus solution are added to a sample of dilute phosphoric acid.

What is the colour of the mixture formed?

State why litmus cannot be used to measure pH.

Phosphoric acid can react to form phosphate salts which are used in fertilisers.

Give two reasons why farmers use fertilisers on their fields.

An experiment was carried out to produce phosphoric acid.

The actual yield for the experiment was 18.62 g.

The theoretical yield for the experiment is 24.50 g.

Calculate the percentage yield of this experiment.

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

The equation for a reaction to make phosphoric acid, H₃PO₄, is

Calculate the atom economy for the production of phosphoric acid in this reaction.

(relative formula masses: Ca₅(PO₄)₃OH = 502, H₂SO₄ = 98, H₃PO₄ = 98, CaSO₄ = 136, H₂O=18)

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

The equation for a reaction to produce phosphoric acid is

Explain how the atom economy of the reaction can be increased.

A student was asked to find the volume of lithium hydroxide solution that would react exactly with 25.0 cm³ of dilute hydrochloric acid.

The student used the equipment in Figure 6 to carry out a rough titration and then a further three accurate titrations.

Which is the name of the piece of equipment labelled X in Figure 6?

Describe how the student should measure the 25.0 cm³ of dilute hydrochloric acid accurately into the conical flask.

Figure 7 shows the results of the student’s titrations.

Calculate the volume of lithium hydroxide solution added in the rough titration.

volume of lithium hydroxide solution =_........ ³

Calculate the mean volume of lithium hydroxide solution used in the accurate titrations.

mean volume of lithium hydroxide solution =_........ ³

Methyl orange indicator was added to dilute hydrochloric acid in the conical flask in the titration.

What colour change would be seen in the conical flask at the end point of the titration?

During the titration, lithium hydroxide solution, LiOH, reacts with dilute hydrochloric acid, HC l, to form lithium chloride, LiC l, and water.

Write the balanced equation for the reaction.

State the name of this type of reaction.

Barium hydroxide reacts with dilute hydrochloric acid to form barium chloride solution and water.

Complete the balanced equation for the reaction by adding a number in front of HC l (aq).

State what you would see during the reaction.

A student investigated how the pH of the mixture changed as barium hydroxide was added to dilute hydrochloric acid.

The student used this method.

step 1 measure out 50 cm3³ of dilute hydrochloric acid into a beaker using a measuring cylinder

step 2 use a glass rod to place a drop of the acid onto a piece of universal indicator paper and record the pH

step 3 add one spatula measure of barium hydroxide to the acid in the beaker and stir

step 4 use the glass rod to place a drop of the mixture onto a new piece of universal indicator paper and record the pH again

step 5 repeat steps 3 and 4 until there is no further change in the pH.

Name a piece of equipment that could be used to measure the pH of a substance more accurately than universal indicator paper.

Explain why, in step 3, the mixture was stirred after adding the barium hydroxide.

Figure 13 shows the student’s results.

Plot a graph of the pH of the mixture against the number of spatula measures of barium hydroxide.

Use the graph to find the pH of the mixture when 4.5 spatula measures of barium hydroxide are added.

Figure 14 shows a hazard symbol on the container of barium hydroxide.

What is the meaning of the hazard symbol in Figure 14?

The barium hydroxide was measured in spatulas.

State one way that the measuring of the barium hydroxide could be improved.

Barium hydroxide reacts with dilute hydrochloric acid to form barium chloride solution and water.

Complete the balanced equation for the reaction by adding a number in front of HC l (aq).

State what you would see during the reaction.

A student investigated how the pH of the mixture changed as barium hydroxide was added to dilute hydrochloric acid.

The student used this method.

step 1 measure out 50 cm3³ of dilute hydrochloric acid into a beaker using a measuring cylinder

step 2 use a glass rod to place a drop of the acid onto a piece of universal indicator paper and record the pH

step 3 add one spatula measure of barium hydroxide to the acid in the beaker and stir

step 4 use the glass rod to place a drop of the mixture onto a new piece of universal indicator paper and record the pH again

step 5 repeat steps 3 and 4 until there is no further change in the pH.

Name a piece of equipment that could be used to measure the pH of a substance more accurately than universal indicator paper.

Explain why, in step 3, the mixture was stirred after adding the barium hydroxide.

Figure 3 shows the student’s results.

Plot a graph of the pH of the mixture against the number of spatula measures of barium hydroxide.

Use the graph to find the pH of the mixture when 4.5 spatula measures of barium hydroxide are added.

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.

In an experiment, powdered calcium hydroxide was added to dilute hydrochloric acid and the pH was measured.

The method used was

step 1 measure 200 cm3³ dilute hydrochloric acid into a beaker

step 2 aadd 0.1 g of powdered calcium hydroxide to the beaker

step 3 find the pH of the mixture

step 4 repeat steps 2 and 3 until the pH stops changing.

State what should be done after step 2 to make sure that any reaction is complete.

Complete the word equation for the reaction.

calcium hydroxide + hydrochloric acid _........

Which row of the table shows the state symbols for powdered calcium hydroxide and dilute hydrochloric acid in the balanced chemical equation?

The results of the experiment are shown in Figure 12.

mass of calcium hydroxide added in grams

Figure 12

Using Figure 12, give the pH of the acid at the start of the experiment.

Using Figure 12, give the mass of calcium hydroxide required to make a neutral mixture.

Explain why the pH starts at a low value and ends at a higher value.

State what should be used to measure the pH of the mixture in this experiment.

The calcium hydroxide used is corrosive to the eyes and an irritant to skin.

Using this information, state one safety precaution that should be taken during the experiment when using any corrosive substance.

In an experiment, powdered calcium hydroxide was added to dilute hydrochloric acid and the pH was measured.

The method used was

step 1 measure 200 cm3³ dilute hydrochloric acid into a beaker

step 2 aadd 0.1 g of powdered calcium hydroxide to the beaker

step 3 find the pH of the mixture

step 4 repeat steps 2 and 3 until the pH stops changing.

State what should be done after step 2 to make sure that any reaction is complete.

Complete the word equation for the reaction.

calcium hydroxide + hydrochloric acid _........

Which row of the table shows the state symbols for powdered calcium hydroxide and dilute hydrochloric acid in the balanced chemical equation?

The results of the experiment are shown in Figure 4.

mass of calcium hydroxide added in grams

Figure 4

Using Figure 4, give the pH of the acid at the start of the experiment.

Using Figure 4, give the mass of calcium hydroxide required to make a neutral mixture.

mass of calcium hydroxide =_........

Explain why the pH starts at a low value and ends at a higher value.

Figure 5 shows part of the reactivity series of metals.

Which metal reacts when added to cold water?

A student investigates the reactivity of four different metals.

The student adds an equal‑sized piece of each metal to separate test tubes containing dilute hydrochloric acid.

The student’s observations for zinc and copper are recorded in Figure 6.

Use the information in Figure 5 and in Figure 6 to predict the observations for the reactions of magnesium and of iron with dilute hydrochloric acid.

magnesium

iron

When metals react with acids, hydrogen gas is produced.

Describe the test to show that the gas is hydrogen.

When magnesium reacts with hydrochloric acid, magnesium chloride and hydrogen are formed.

Complete the balanced equation for the reaction.

An excess of magnesium is added to some dilute hydrochloric acid of pH 2. The mass of hydrogen gas produced is measured.

The experiment is repeated with excess magnesium but with the same volume of dilute hydrochloric acid of pH 1.

State how many times greater the concentration of hydrogen ions is in the acid of pH 1 than in the acid of pH 2.

With the acid of pH 2, the mass of hydrogen gas produced when the reaction is complete is 0.005 g.

Predict the mass of hydrogen gas produced in the reaction with acid of pH 1.

Titration is used to carry out some neutralisation reactions.

Ammonium nitrate can be made by neutralisation.

State the name of the two reactants that are neutralised to make the salt ammonium nitrate.

Ammonium nitrate is a fertiliser. Another fertiliser is ammonium phosphate.

Which elements are combined in ammonium phosphate?

Titrations involve aqueous solutions and the use of burettes.

Figure 8 shows readings on part of a burette at the start and at the end of a titration.

Calculate the volume of solution added from this burette.

Give your answer to a suitable number of decimal places.

A student carries out a titration four times.

The volumes from the student’s results table are shown in Figure 9.

Tick the volumes that should be used to calculate the mean volume.

Figure 10 shows the burette and flask prepared for use by the student. The burette is supported vertically by a clamp that is not shown in the diagram.

The student wrote a description of how they used the burette.

Give three improvements to the way that the student used the burette.

In a titration a student placed alkali in the flask.

By mistake a few drops of litmus and a few drops of phenolphthalein were added to the flask.

The student added acid to the flask until the mixture was acidic.

Predict the colour change that would be seen.

In a titration a student rinsed out the flask with distilled water and did not dry it.

They used the flask for titration, adding the solution from the burette until the indicator changed colour.

State the effect, if any, on the titre volume of using the wet flask rather than a dry flask.

A student wanted to find the volume of dilute hydrochloric acid that would react with 25.0 cm³ of lithium hydroxide solution.

They used the equipment in Figure 7 to carry out a rough titration and then a further two accurate titrations.

Suggest why the student carried out a rough titration before the two accurate titrations.

Figure 8 shows the results of the rough titration.

What was the volume of acid added in the rough titration?

Describe how the rough titration should be carried out once the dilute hydrochloric acid, lithium hydroxide solution and indicator are placed in the apparatus in Figure 7.

Which is the name of an indicator that is suitable to use in this titration?

During the titration the dilute hydrochloric acid, HC l, is reacting with the lithium hydroxide solution, LiOH.

Explain what type of reaction is taking place in the titration.

Barium hydroxide reacts with dilute hydrochloric acid to form barium chloride and water.

The equation for the reaction is

Which row of the table shows the correct state of each of the substances in the equation for the reaction?

Name a piece of equipment which could be used to measure out 50.0 cm³ of dilute hydrochloric acid more accurately than the measuring cylinder.

Describe how the pH of the mixture is determined when a drop of it is placed on the universal indicator paper.

In the method, universal indicator paper is used to determine the pH.

Explain why litmus paper would not be a suitable indicator to use in this experiment.

Figure 14 shows the student’s results.

On the grid opposite:

• Add suitable scales to the vertical and horizontal axes.

• Plot a graph of the pH of the mixture against the mass of barium hydroxide.

Figure 15 shows a hazard symbol placed on a container of barium hydroxide.

What is the meaning of the hazard symbol in Figure 15?

Barium hydroxide is also corrosive.

Give one precaution that the student should take when using barium hydroxide.

Barium hydroxide reacts with dilute hydrochloric acid to form barium chloride and water.

The equation for the reaction is

Which row of the table shows the correct state of each of the substances in the equation for the reaction?

A student wanted to investigate how the pH of the mixture changes as barium hydroxide is added to dilute hydrochloric acid.

They followed this method.

step 1 measure out 50.0 cm3³ of dilute hydrochloric acid into a beaker using a measuring cylinder step 2 use a glass rod to place a drop of the acid onto a piece of universal indicator paper and record the pH step 3 add 0.2 g of barium hydroxide to the acid in the beaker and stir step 4 use the glass rod to place a drop of the mixture onto a new piece of universal indicator paper and record the pH again step 5 repeat steps 3–4 until there is no further change in the pH.

Name a piece of equipment which could be used to measure out 50.0 cm³ of dilute hydrochloric acid more accurately than the measuring cylinder.

Describe how the pH of the mixture is determined when a drop of it is placed on the universal indicator paper.

In the method, universal indicator paper is used to determine the pH.

Explain why litmus paper would not be a suitable indicator to use in this experiment.

Figure 2 shows the student’s results.

On the grid opposite:

• Add suitable scales to the vertical and horizontal axes.

• Plot a graph of the pH of the mixture against the mass of barium hydroxide.

The volume of dilute sulfuric acid required to neutralise 25.0 cm³ of ammonia solution can be found by titration.

In the titration, a few drops of methyl orange indicator were added to the ammonia solution in a conical flask before adding the dilute sulfuric acid.

State the change in colour of the methyl orange at the end point when the ammonia solution has just been neutralised.

When the ammonia solution was neutralised by the dilute sulfuric acid, a solution of ammonium sulfate was formed.

Complete the balanced equation for the reaction between ammonia solution and sulfuric acid.

The titration was repeated to obtain a mean volume of dilute sulfuric acid required to neutralise the 25.0 cm³ of ammonia solution. The volumes of the two solutions were measured accurately.

Explain two other practical steps that should be used in the titration to ensure that an accurate titre volume is obtained.

The mean volume of dilute sulfuric acid required to neutralise the ammonia solution was determined from the results of the titration.

This volume of dilute sulfuric acid was added to 25.0 cm³ of ammonia solution in a conical flask.

Devise a plan to produce a sample of dry ammonium sulfate from the contents of the conical flask.

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.

Hydrochloric acid reacts with solid B. Solid B is an alkali.

A student carries out an experiment to see how the pH changes when different masses of solid B are added to dilute hydrochloric acid.

The student uses the following method.

step 1 use a measuring cylinder to measure out 100cm³ of dilute hydrochloric acid

step 2 pour the acid into a beaker

step 3 measure the pH with a pH probe

step 4 add half a spatula of solid B and stir

step 5 repeat steps 3 and 4 until the pH stops changing.

Give a safety precaution that should be taken during the experiment.

Give an improvement to step 4 that would produce more accurate results.

What is the most likely change in pH during the experiment?

If some methyl orange indicator is added to the acid in step 2, the mixture changes colour during the experiment.

State the colour change.

colour at start in acid_........ colour at end_........

Concentrated hydrochloric acid can be broken down using electricity. The apparatus that can be used is shown in Figure 6.

Give the name of the piece of apparatus labelled X.

The rod labelled Y in Figure 6 is made of graphite.

What is the name of this piece of apparatus?

Give one reason why graphite is a suitable material to make Y.

Complete the balanced equation for the reaction that occurs.

The scientist John Dalton lived over 200 years ago.

John Dalton suggested an early model of atoms.

When Dalton first described atoms he said that

• all elements are made of atoms

• atoms are not formed of any smaller particles

• all atoms of the same element are identical.

Give two differences between Dalton’s model of atoms and today’s model of atoms.

Dalton also investigated different gases.

One of the gases that Dalton investigated was ethene.

The structure of one molecule of ethene is shown in Figure 8.

Give the molecular formula and the empirical formula of ethene.

Another gas that Dalton investigated was chlorine.

Chlorine gas reacts with water. The two products are a solution of hydrogen chloride and the substance HC l O.

Complete the balanced equation for this reaction, including the three missing state symbols.

Hydrogen chloride solution is acidic.

The formulae of four ions are shown in Figure 9.

Give the formula of the ion in Figure 9 that causes the hydrogen chloride solution to be acidic.

An acid reacts with an alkali.

Give the name of this type of reaction.

Describe what you would see when some copper carbonate powder is added to a beaker of dilute sulfuric acid.

The scientist John Dalton lived over 200 years ago.

John Dalton suggested an early model of atoms.

When Dalton first described atoms he said that

• all elements are made of atoms

• atoms are not formed of any smaller particles

• all atoms of the same element are identical.

Give two differences between Dalton’s model of atoms and today’s model of atoms.

Dalton also investigated different gases.

One of the gases that Dalton investigated was ethene.

The structure of one molecule of ethene is shown in Figure 2.

Give the molecular formula and the empirical formula of ethene.

Another gas that Dalton investigated was chlorine.

Chlorine gas reacts with water. The two products are a solution of hydrogen chloride and the substance HC l O.

Complete the balanced equation for this reaction, including the three missing state symbols.

Hydrogen chloride solution is acidic.

The formulae of four ions are shown in Figure 3.

Give the formula of the ion in Figure 3 that causes the hydrogen chloride solution to be acidic.

An acid reacts with an alkali.

Give the name of this type of reaction.

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 =_........

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 =_........

When solid sodium chloride is mixed with water, sodium chloride solution forms.

What name is given to the process of mixing a solid with water to form a solution?

Sodium reacts with hydrochloric acid to form sodium chloride and hydrogen.

Write the word equation for this reaction.

The hazard symbol shown in Figure 1 is used on containers of sodium.

What is the meaning of this hazard symbol?

Hydrogen has one electron in its electron shell. Figure 2 shows the incomplete dot and cross diagram of a hydrogen molecule.

Complete Figure 2 to show the electrons in the covalent bond between the two atoms of hydrogen.

The pH of a sodium chloride solution was measured.

State what could be used to measure the pH of a solution.

Sodium chloride solution is neutral.

Give the pH of this solution.

Dilute hydrochloric acid is a strong acid.

Explain why dilute hydrochloric acid is described as a strong acid.

1 cm³ of hydrochloric acid of pH 2 is made up to a volume of 10 cm³ with distilled water.

State the pH of the new solution.

Magnesium oxide reacts with dilute hydrochloric acid to produce magnesium chloride solution and water.

Write the ionic equation for this reaction.

In an experiment magnesium hydroxide powder is added in 0.1 g portions to 25 cm³ of dilute hydrochloric acid until the magnesium hydroxide is just in excess.

Universal indicator paper can be used to test the pH of the solution after each addition of magnesium hydroxide.

Give the name of an alternative piece of equipment that can be used to measure pH.

State and explain how the pH changes as the magnesium hydroxide is added to the dilute hydrochloric acid.

(a) X and Y are solutions of two different acids. The concentration of acid in each solution, in mol dm⁻³, is the same. Solution X has a pH of 3.40 and solution Y has a pH of 4.40.

State what could be used to measure these pH values of 3.40 and 4.40.

What is the concentration of hydrogen ions in solution X compared with that in solution Y ?

An experiment is planned to record the change in pH as a powdered base is added to 50 cm³ dilute hydrochloric acid.

The method suggested is

step 1 add dilute hydrochloric acid up to the 50 cm³ mark on a beaker

step 2 add one spatula of the base and stir

step 3 measure the pH of the mixture

step 4 repeat steps 2 and 3 until the pH stops changing.

State how you could change the method so that the amounts of dilute hydrochloric acid and of the base can be measured more accurately.

dilute hydrochloric acid_........

During the experiment the pH changes from 2 to 10. If phenolphthalein indicator is added at the beginning of the experiment, a colour change occurs as the base is added.

State the colour change that occurs.

Explain, in terms of the particles present, why the pH increases during the experiment.

*(c) Some properties of four solids, A, B, C and D, are shown in Figure 6.

The solids, in no particular order, are copper carbonate, copper oxide, magnesium metal and sodium hydroxide.

Identify the solids A, B, C and D, explaining how the information in Figure 6 supports the identification of each solid.

(a) Nitric acid can be titrated with a solution of ammonia.

State the type of reaction occurring when nitric acid reacts with ammonia.

What salt is formed in this reaction?

In one stage of the production of nitric acid, nitrogen oxide, NO, is reacted with oxygen to make nitrogen dioxide, NO₂.

Calculate the minimum volume of air, measured at room temperature and pressure, required to react with 1000 g nitrogen oxide to form nitrogen dioxide.

Assume that the air contains 20% oxygen by volume. (relative atomic masses: N = 14, O = 16 1 mol of gas occupies 24 dm³ at room temperature and pressure)

*(c) In another stage in the production of nitric acid, ammonia is reacted with oxygen to form nitrogen oxide and water.

Heat energy is given out when ammonia reacts with oxygen.

The conditions chosen for the reaction are

• excess air, rather than just the right amount

• a pressure of 10 atm, rather than atmospheric pressure

• a temperature of 900 °C, rather than room temperature.

Explain the effect of the conditions chosen on the equilibrium yield of nitrogen oxide and on the rate of attainment of equilibrium.

(a) A titration of sodium hydroxide solution with hydrochloric acid can be carried out as follows

1 a pipette is used to measure 25.00 cm³ of sodium hydroxide solution into a conical flask 2 a few drops of indicator are added to the sodium hydroxide solution 3 the burette is filled with hydrochloric acid 4 the hydrochloric acid is added to the sodium hydroxide solution until the indicator changes colour.

Describe how the pipette should be used to measure exactly 25.00 cm³ of sodium hydroxide solution into the conical flask.

The burette is first washed with water. It is then rinsed with some of the acid before it is filled with the acid to begin the titration.

Explain why the burette is rinsed with the acid.

Universal indicator solution is not a suitable indicator for an acid-alkali titration.

Give the name of an indicator that is suitable for use in the titration of sodium hydroxide solution with hydrochloric acid.

Universal indicator goes through a series of gradual colour changes as the pH changes in a solution.

Give a reason why universal indicator is not a suitable indicator to use in an acid-alkali titration.

Figure 3 shows some titration results obtained from an experiment in which an alkali is titrated with an acid.

Calculate the accurate volume of acid reacting with the alkali.

accurate volume of acid reacting_........

(a) A student placed a piece of metal P in a test tube containing excess dilute sulfuric acid. The student repeated this with three other metals, Q, R and S. All the pieces of all four metals were the same size.

The student recorded the observations until each metal had reacted with the acid for two minutes. The observations are shown in Figure 9.

Use this information to put the four metals in order of reactivity from the least reactive to the most reactive.

least reactive
most reactive

Complete the diagram below to show how the student could add to the apparatus to measure the volume of gas produced in the two minutes.

When iron reacts with copper sulfate solution, solid copper is formed.

Two possible equations for this reaction are

A CuSO₄ + Fe Cu + FeSO₄ B 3CuSO₄ + 2Fe 3Cu + Fe₂(SO₄)₃

It was found that 10.00 g of iron powder reacted with excess copper sulfate solution to produce 11.34 g of copper.

Carry out a calculation to decide which equation, A or B, represents the reaction taking place. (relative atomic masses: Fe = 56.0, Cu = 63.5)

Acid solutions contain hydrogen ions.

Aluminium reacts with dilute hydrochloric acid to form a solution containing aluminium ions, Al³⁺.

Complete the balanced ionic equation for this reaction.

The hydrogen ion concentration in a solution is decreased by a factor of 10.

State how the pH of this solution changes.

Calculate the mass, in g, of a hydrogen atom, using the data below. (relative atomic mass: H = 1.00; Avogadro constant = 6.02 × 10²³)

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