The pH scale and neutralisation

This question is about ammonia.

Ammonia is a gas.

Suggest why the litmus paper used to test for ammonia gas has to be damp.

Ammonia can be made on an industrial scale using the Haber process.

The equation for the reaction is

The reaction can reach a dynamic equilibrium.

Explain what happens when the reaction reaches dynamic equilibrium.

Figure 4 shows the changes in percentage yield of ammonia at equilibrium as temperature increases, at a pressure of 300 atmospheres and at a pressure of 1000 atmospheres.

Which row of the table will give the highest percentage yield of ammonia at equilibrium?

In industry, a pressure of 200 atmospheres is used for the Haber process.

Using Figure 4, explain what happens to the position of dynamic equilibrium if the process is carried out at 100 atmospheres.

Ammonia can also be made by heating ammonium chloride.

A sample of solid ammonium chloride is heated in a boiling tube.

After a few minutes ammonium chloride, a white solid, is also seen at the top of the boiling tube, as shown in Figure 5.

Explain how ammonium chloride is formed at the top of the boiling tube.

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).

Ba(OH)₂(s) +_........ HCl(aq) BaCl₂(aq) + 2H₂O(l)

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 7 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.

pH of the mixture =_........

Figure 8 shows a hazard symbol on the container of barium hydroxide.

What is the meaning of the hazard symbol in Figure 8?

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).

Ba(OH)₂(s) +_........ HCl(aq) BaCl₂(aq) + 2H₂O(l)

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 1 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.

pH of the mixture =_........

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 7.

mass of calcium hydroxide added in grams

Figure 7

Using Figure 7, give the pH of the acid at the start of the experiment.

pH =_........

Using Figure 7, give the mass of calcium hydroxide required to make a neutral mixture.

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

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 1.

mass of calcium hydroxide added in grams

Figure 1

Using Figure 1, give the pH of the acid at the start of the experiment.

pH =_........

Using Figure 1, give the mass of calcium hydroxide required to make a neutral mixture.

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

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

Figure 2 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 3.

Use the information in Figure 2 and in Figure 3 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.

Mg +_........ HCl MgCl₂ +_........

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.

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

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 8 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 9 shows a hazard symbol placed on a container of barium hydroxide.

What is the meaning of the hazard symbol in Figure 9?

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 1 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.

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 1 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 1 that shows that the drinking water is neutral.

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

mass =_........ mg

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 4.

Give the name of the piece of apparatus labelled X.

The rod labelled Y in Figure 4 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.

_........ HCl H₂ + Cl₂

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 5.

Give the molecular formula and the empirical formula of ethene.

molecular formula_........

empirical formula_........

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 6.

Give the formula of the ion in Figure 6 that causes the hydrogen chloride solution to be acidic.

formula_........

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.

A sample of potable water contains impurities.

Why is this sample of water potable even though it contains impurities?

Waste water can be used to produce drinking water. The processes used include sedimentation, filtration and chlorination.

What is sedimentation?

State why the waste water is filtered.

State the reason for chlorination.

Some salts can be added to waste water to remove impurities. In an experiment, different masses of salt A were added to 1000cm³ samples of waste water. The experiment was repeated with salt B. The percentages of impurities removed from the waste water are shown in Figure 7.

mass of salt in mg per 1000cm³ water

Figure 7

It was concluded that the best way to purify 1000cm³ of the waste water is to add 100 mg of salt B.

Use the information about salt A and salt B in Figure 7 to evaluate this conclusion.

*(d) A sample of water was contaminated with a dissolved solid.

Devise a plan to separate pure water from this mixture, including a test to show that the water obtained is neutral.

You may use some or all of the apparatus shown in Figure 8 and any other laboratory apparatus.

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 1.

Give the molecular formula and the empirical formula of ethene.

molecular formula_........

empirical formula_........

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 2.

Give the formula of the ion in Figure 2 that causes the hydrogen chloride solution to be acidic.

formula_........

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.

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 =_........ g

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.

In the 19th century, Mendeleev arranged the elements known at the time to form his periodic table. Mendeleev’s periodic table is different from the modern periodic table.

State one difference between Mendeleev’s periodic table and the modern periodic table.

Aluminium oxide reacts with hydrochloric acid to form a salt and water.

State the name of the salt formed.

In this reaction aluminium oxide is a base.

State the type of reaction that takes place when an acid reacts with a base.

Gallium, Ga, is in the same group of the modern periodic table as aluminium.

The formula of aluminium oxide is Al₂O₃.

Predict the formula of gallium oxide.

Gallium oxide has a very high melting point. Gallium oxide does not conduct electricity when solid but does conduct electricity when molten.

What type of substance is gallium oxide?

Figure 5 shows the changes of state for gallium and the arrangement of particles in liquid gallium.

Complete the boxes for solid gallium and gaseous gallium by drawing the arrangement of the particles in each of these physical states.

Give the name of the change of state labelled Y in Figure 5.

Gallium metal is a conductor of electricity.

Explain how metals conduct electricity.

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.

pH =_........

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_........

base_........

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.

colour at start_........

colour at end_........

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 3.

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 3 supports the identification of each solid.

(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 6.

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

least reactive
most reactive

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.

_........ +_........ H⁺ _........ Al³⁺ +_........

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)

mass of hydrogen atom =_........ g