Reactions of acids

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.

Sodium carbonate has the formula Na₂CO₃.

Sodium carbonate contains Na⁺ ions and CO₃^2– ions.

The atomic number of sodium is 11.

What is the electronic configuration of the Na⁺ ion?

Explain why solid sodium carbonate cannot conduct electricity but a solution of sodium carbonate can conduct electricity.

Calculate the percentage by mass of sodium in sodium carbonate, Na₂CO₃.

(relative atomic masses: C = 12, O = 16, Na = 23)

percentage by mass of sodium =_........

*(c) A student has three solids, A, B and C.

The solids are sodium carbonate, powdered zinc and copper oxide, but the student does not know which solid is which.

The student reacted each solid with dilute sulfuric acid.

Figure 9 shows the student’s observations and the results of tests on any gases produced.

Use the observations and results in Figure 9 to identify which solid is which.

Your answer should include

• how each test result helps you to identify the solid

• word equations to support your answer.

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 =_........

Figure 8 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 9.

Use the information in Figure 8 and in Figure 9 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 +_........

*(c) There are three common methods of obtaining metals from the Earth’s crust:

• mine the pure metal

• mine the metal ore and heat it with carbon

• mine the metal ore and electrolyse the molten compound.

The method used to obtain a metal is linked to its position in the reactivity series of metals.

Aluminium, gold, iron, and silver are some commonly used metals.

Use the reactivity series in Figure 8 to state and explain the method chosen to obtain each of these four metals.

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.

Crystals of copper sulfate are prepared by reacting copper oxide, a base, with dilute sulfuric acid.

Name the other product of this reaction.

During the experiment, a spatula measure of copper oxide, a black powder, is added to warm, dilute sulfuric acid in a beaker.

When the mixture is stirred, the black powder disappears and the mixture turns pale blue.

The student then adds more copper oxide until the maximum amount of copper sulfate is formed without wasting copper oxide.

Explain how the student knows when to stop adding copper oxide.

The reaction produces an aqueous solution of copper sulfate.

What is the best way to obtain crystals of copper sulfate from an aqueous solution?

When some water is removed from the aqueous solution of copper sulfate, crystals of copper sulfate are made.

Describe how the arrangement and movement of the particles change as crystals are formed from a solution.

In this reaction, copper oxide, CuO, forms copper sulfate, CuSO₄.

Explain, in terms of electrons, whether the copper in copper oxide has been oxidised, has been reduced, or has not been oxidised or reduced.

In another experiment, a copper sulfate solution with a concentration of 39.875 g dm^–3 is used.

Calculate the mass of copper sulfate dissolved in 0.300 dm³ of this solution.

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

Magnesium carbonate has the formula MgCO₃.

Magnesium carbonate contains Mg²⁺ and CO₃²⁻ ions.

The atomic number of magnesium is 12.

What is the electronic configuration of the Mg²⁺ ion?

Explain why solid magnesium carbonate cannot conduct electricity but solid magnesium can.

Calculate the percentage by mass of magnesium in magnesium carbonate, MgCO₃.

(relative atomic masses: C = 12.0, O = 16.0, Mg = 24.0)

percentage by mass of magnesium =_........

*(c) A student has two separate test tubes containing sulfuric acid.

The student adds a spatula measure of magnesium carbonate, MgCO₃, to the first test tube and a piece of magnesium to the second test tube.

Explain what the student would see in each test tube and the tests that they should carry out to identify the gases produced.

Your answer should include word equations for the reactions that would take place.

Magnesium carbonate has the formula MgCO₃.

Magnesium carbonate contains Mg²⁺ and CO₃²⁻ ions.

The atomic number of magnesium is 12.

What is the electronic configuration of the Mg²⁺ ion?

Explain why solid magnesium carbonate cannot conduct electricity but solid magnesium can.

Calculate the percentage by mass of magnesium in magnesium carbonate, MgCO₃.

(relative atomic masses: C = 12.0, O = 16.0, Mg = 24.0)

percentage by mass of magnesium =_........

Magnesium carbonate reacts with dilute hydrochloric acid. Water and carbon dioxide are two of the products of the reaction.

Complete the balanced equation for this reaction.

MgCO₃ + 2HCl _........ + H₂O + CO₂

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.

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.

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.

The word equation for the reaction between copper carbonate and dilute sulfuric acid is

copper sulfuric copper carbon

Complete the balanced equation for this reaction.

CuCO₃+_{........ ........} + CO₂+ H₂O

Calculate the relative formula mass of copper carbonate, CuCO₃. (relative atomic masses: C = 12.0, O = 16.0, Cu = 63.5)

relative formula mass of CuCO₃ =_........

What is the chemical test to show that a gas is carbon dioxide?

Figure 7 shows a conical flask containing dilute sulfuric acid. Copper carbonate is added to the acid in the flask. The copper carbonate is added one spatula measure at a time until the reaction has finished.

State two observations that would show the reaction has finished.

The word equation for the reaction between copper carbonate and dilute sulfuric acid is

copper sulfuric copper carbon

Complete the balanced equation for this reaction.

CuCO₃+_{........ ........} + CO₂+ H₂O

Calculate the relative formula mass of copper carbonate, CuCO₃. (relative atomic masses: C = 12.0, O = 16.0, Cu = 63.5)

relative formula mass of CuCO₃ =_........

What is the chemical test to show that a gas is carbon dioxide?

Figure 2 shows a conical flask containing dilute sulfuric acid. Copper carbonate is added to the acid in the flask. The copper carbonate is added one spatula measure at a time until the reaction has finished.

State two observations that would show the reaction has finished.

The electronic configuration of carbon is 2.4 The electronic configuration of oxygen is 2.6

Draw a dot and cross diagram for a molecule of carbon dioxide.

Show outer electrons only.

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