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GCSE Chemistry · GCSEChapter 10 · Reactions of acids and making salts
GCSE · Chapter 10

Reactions of acids and making salts

By the end of this chapter you will be able to

  • Use universal indicator and the pH scale to classify solutions
  • Name a salt from the acid and the metal in it, and write word equations for neutralisation
  • Describe each step of making a pure, dry sample of a soluble salt
  • Explain the difference between strong and weak acids, and between strength and concentration
  • [H] Calculate a concentration from titration results, and write the ionic equation

You should already know

  • Ions and charges (Chapter 4)
  • Concentration in g/dm3 and moles (Chapters 8 and 9)

Where this leads

  • Electrolysis of solutions and products at electrodes (Chapter 11)
  • Quantitative analysis of substances (Chapter 17)

GCSE Chemistry. Content follows the GCSE (9-1) subject content for England (Edexcel and AQA). Content references: Use the pH scale and indicators to classify solutions as acidic, neutral or alkaline, Explain acids as sources of H+ ions and alkalis as sources of OH- ions, Describe neutralisation and name the salts made from acids and bases, Carry out the practical to prepare a pure, dry sample of a soluble salt, safely, [H] Write the ionic equation for neutralisation, and use titration to find a concentration.

Exercise P  Do you remember?

1
FWhat is the charge of a hydrogen ion, H+? Write the sign and number.
2
FWhich group are the alkali metals in? Write the number.
3
FWhat is the formula of copper oxide? Write the formula.
4
FWhat is the Mr of H2O? Write the number.
5
FWrite 10-3 as a decimal. Write the number.
10.1

The pH scale and indicators

GCSE
Use the pH scale and indicators to classify solutions as acidic, neutral or alkaline
Video lesson: The pH scale and indicatorsComing soon
Context. Ruth tests the water in a fish tank with universal indicator. The colour is green. “Is the water neutral?” she asks. The pH scale tells us how acidic or alkaline a solution is: green means pH 7, which is neutral.

The pH scale runs from 0 to 14. Solutions with a pH below 7 are acidic; pH 7 is neutral; solutions above 7 are alkaline. The lower the pH, the more acidic the solution. An indicator changes colour with the pH. Universal indicator shows a range of colours across the whole scale.

pH scale and universal indicator (simplified colours)01234567891011121314acidneutral (pH 7)alkali
The pH scale with the colours of universal indicator (simplified)
IndicatorIn acidIn alkaliNeutral
litmusredbluepurple
universal indicatorred to orangeblue to violetgreen
Colours of some indicators

Key ideas

  • pH below 7: acidic; pH 7: neutral; pH above 7: alkaline.
  • Universal indicator shows the pH by its colour, from red (acid) to violet (alkali).
  • Litmus is red in acid and blue in alkali.
  • pH is measured on a scale; each whole-number step is a tenfold change in H+ concentration.
Worked example 10.1.1
Universal indicator turns orange when added to a solution. What is the pH range of the solution, to the nearest number? Write the pH as one number.

Method. Find orange on the colour scale.

  1. Look. Orange is near the acid end of the scale, at about pH 3.
    pH 3
  2. Decide. The solution is acidic.
    acidic
  3. Write the answer.
    3

Check. Red is the strongest acid colour, around pH 1. ✓

Worked example 10.1.2
A solution turns litmus paper blue. Is the solution acidic, neutral or alkaline? Write the word.

Method. Recall what litmus does.

  1. Recall. Litmus turns blue in alkali.
    blue in alkali
  2. Decide. So the solution is alkaline.
    alkaline
  3. Write the answer.
    alkaline

Check. Litmus is red in acid. ✓

Worked example 10.1.3
A solution has pH 2. Is it more or less acidic than a solution of pH 5? Write the word.

Method. Compare the pH values.

  1. Compare. A lower pH means a more acidic solution.
    lower
  2. Decide. So pH 2 is more acidic than pH 5.
    more
  3. Write the answer.
    more

Check. Each pH step is a tenfold change. ✓

Watch out

Watch out: a lower pH means more acidic, not less. Do not read the scale backwards.

Exam tip

Exam tip. When you describe an indicator colour, give the colour and the pH range it suggests.

Exercise 10A  The pH scale and indicators

1
FWhat is the pH of a neutral solution? Write the number.
2
FIs a solution with pH 3 acidic, neutral or alkaline? Write the word.
3
FIs a solution with pH 11 acidic, neutral or alkaline? Write the word.
4
FWhat colour does litmus turn in an alkali? Write the colour.
5
FWhat colour does universal indicator turn in a neutral solution? Write the colour.
6
FWhich has the lower pH: a solution that is pink in universal indicator, or one that is blue? Write the colour.
7
FWhat does a pH of 7 mean for the concentration of H+ and OH- ions? Write one word: equal or unequal.
8
FName the indicator that can show the whole pH scale in colours. Write the name.
9
PSA solution is red in universal indicator. What is its approximate pH? Write the number.
10
PSA solution is purple in universal indicator. Is it acidic, neutral or alkaline? Write the word.
11
RExplain why a pH of 2 is more acidic than a pH of 4, in one sentence. Accept any sentence that says a lower pH means a higher concentration of H+ ions.
12
RA pupil says “universal indicator is green, so the solution is acidic.” Explain why this is wrong, in one sentence. Accept any sentence that says green means pH 7, which is neutral.
10.2

Acids, alkalis and their ions

GCSE
Explain acids as sources of H+ ions and alkalis as sources of OH- ions
Video lesson: Acids, alkalis and their ionsComing soon
Context. A pupil says that acids and alkalis are “opposites”. “What makes a solution acidic?” asks the teacher. The answer is in the ions the solution contains: acids release H+ ions, and alkalis release OH- ions.

An acid is a substance that produces H+ ions in aqueous solution. An alkali is a soluble base that produces OH- ions in aqueous solution. The more H+ ions a solution has, the lower its pH. A base is a substance that neutralises an acid; an alkali is a base that dissolves in water.

H<sup>+</sup>acid+OH<sup>-</sup>alkalireact
An acid gives H+ ions and an alkali gives OH- ions; they combine to make water

Key ideas

  • Acids produce H+ ions in water.
  • Alkalis produce OH- ions in water.
  • In neutralisation, H+ and OH- combine to form water: H+ + OH- -> H2O.
  • A base is any substance that neutralises an acid; an alkali is a soluble base.
Worked example 10.2.1
Which ion makes a solution acidic? Write the ion.

Method. Recall what acids produce.

  1. Recall. Acids produce hydrogen ions in water.
    hydrogen ions
  2. Write. The ion is H+.
    H+
  3. Write the answer.
    H+

Check. H+ is a proton. ✓

Worked example 10.2.2
Which ion makes a solution alkaline? Write the ion.

Method. Recall what alkalis produce.

  1. Recall. Alkalis produce hydroxide ions in water.
    hydroxide ions
  2. Write. The ion is OH-.
    OH-
  3. Write the answer.
    OH-

Check. OH- has a charge of -1. ✓

Worked example 10.2.3
[H] Write the ionic equation for neutralisation. Write it with H+ and OH-.

Method. H+ and OH- combine to form water.

  1. Reactants. H+ from the acid and OH- from the alkali.
    H+ and OH-
  2. Product. They combine to form water.
    H2O
  3. Write the answer.
    H+ + OH- -> H2O

Check. The charges balance: +1 - 1 = 0. ✓

Watch out

Watch out: an acid is not an acid because it has a lot of water in it. The acid property comes from the H+ ions it releases.

Exam tip

Exam tip. Use the words “H+ ions” and “OH- ions” in your answers about acids and alkalis.

Exercise 10B  Acids, alkalis and their ions

1
FWhich ion do acids produce in water? Write the ion.
2
FWhich ion do alkalis produce in water? Write the ion.
3
FWhat is the name of the substance that neutralises an acid? Write the word.
4
FIs an alkali a soluble base? Write yes or no.
5
FWhat do the H+ and OH- ions form in neutralisation? Write the formula.
6
FName the ion that makes a solution alkaline. Write the formula.
7
PSWhich ion is in both acids and water? Write the ion. (Hint: the same ion gives acids their property.)
8
PS[H] Write the ionic equation for neutralisation, with the state symbol for water as (l). Write the equation.
9
RExplain why a solution of an acid conducts electricity, in one sentence. Accept any sentence that says the H+ ions are free to move and carry charge.
10
RExplain why neutralisation happens when an acid meets an alkali, in one sentence. Accept any sentence that says H+ ions and OH- ions combine to form water.
11
RA pupil says “a solution with a lot of acid has a high pH.” Explain why this is wrong, in one sentence. Accept any sentence that says more acid gives more H+ ions, so the pH is lower.
10.3

Neutralisation and making salts

GCSE
Describe neutralisation and name the salts made from acids and bases
Video lesson: Neutralisation and making saltsComing soon
Context. A school chemist wants to make a salt from an acid and a base. “Which metal gives which salt?” asks a pupil. The name of the salt comes from the metal and the acid: sulfuric acid gives sulfates, hydrochloric acid gives chlorides, and nitric acid gives nitrates.

An acid reacts with a base (a metal oxide, a metal hydroxide or a metal carbonate) to form a salt and water. This is neutralisation. Acids also react with some metals to form a salt and hydrogen. The name of the salt has two parts: the metal first, then the acid part (sulfate, chloride or nitrate).

BaseWord equation with an acidGives
metal oxidecopper oxide + sulfuric acid -> copper sulfate + watersalt and water
metal hydroxidesodium hydroxide + hydrochloric acid -> sodium chloride + watersalt and water
metal carbonatemagnesium carbonate + hydrochloric acid -> magnesium chloride + water + carbon dioxidesalt, water and carbon dioxide
metalmagnesium + hydrochloric acid -> magnesium chloride + hydrogensalt and hydrogen
Reactions of acids with bases and metals
AcidSalt ends withExample
sulfuric acid, H2SO4sulfatecopper sulfate
nitric acid, HNO3nitratepotassium nitrate
hydrochloric acid, HClchloridesodium chloride
Naming salts from the acid

Key ideas

  • Acid + metal oxide or hydroxide -> salt + water.
  • Acid + metal carbonate -> salt + water + carbon dioxide.
  • Acid + metal -> salt + hydrogen (metals above copper in the reactivity series).
  • Sulfuric acid gives sulfates; hydrochloric acid gives chlorides; nitric acid gives nitrates.
Worked example 10.3.1
Name the salt made when sulfuric acid reacts with copper oxide. Write the name.

Method. Use the metal and the acid part.

  1. Metal. The metal is copper.
    copper
  2. Acid. Sulfuric acid gives sulfate.
    sulfate
  3. Salt. So the salt is copper sulfate.
    copper sulfate
  4. Write the answer.
    copper sulfate

Check. The other products are water. ✓

Worked example 10.3.2
Write the word equation for hydrochloric acid reacting with sodium hydroxide. Write the products.

Method. Neutralisation gives a salt and water.

  1. Reactants. Hydrochloric acid and sodium hydroxide.
    acid + alkali
  2. Products. The salt is sodium chloride, and the other product is water.
    sodium chloride + water
  3. Write the answer.
    sodium chloride and water

Check. The salt is NaCl. ✓

Worked example 10.3.3
Name the gas made when magnesium carbonate reacts with hydrochloric acid, and the salt. Write the names, gas then salt.

Method. Carbonates give carbon dioxide and water as well as a salt.

  1. Gas. Carbon dioxide is released.
    carbon dioxide
  2. Salt. The salt is magnesium chloride.
    magnesium chloride
  3. Write the answer.
    carbon dioxide, magnesium chloride

Check. Water is also made. ✓

Watch out

Watch out: a salt is not an acid or an alkali. Its name is the metal followed by the acid part, so do not name it “copper acid”.

Exam tip

Exam tip. Write the metal first, then the acid part (sulfate, chloride, nitrate). Check the number of products: salt and water for oxides; salt, water and carbon dioxide for carbonates.

Exercise 10C  Neutralisation and making salts

1
FWhat is the name of the salt made from sulfuric acid? Write the ending.
2
FWhat is the name of the salt made from hydrochloric acid? Write the ending.
3
FWhat is the name of the salt made from nitric acid? Write the ending.
4
FName the salt made from sodium hydroxide and hydrochloric acid. Write the name.
5
FWrite the word equation: copper oxide + sulfuric acid -> ... Write the name of the salt formed.
6
FWhich other product, besides a salt, is made when a metal oxide reacts with an acid? Write the name.
7
FWhich gas is made when a metal carbonate reacts with an acid? Write the name.
8
FWhich gas is made when a metal reacts with dilute hydrochloric acid, for a metal above copper in the series? Write the name.
9
PSWrite the word equation for magnesium carbonate reacting with hydrochloric acid. Write the names of the products.
10
PSA pupil reacts zinc oxide with nitric acid. Name the salt. Write the name.
11
RExplain why a salt is made, not a new acid, when an acid neutralises a metal oxide, in one sentence. Accept any sentence that says the metal replaces the hydrogen ions of the acid.
12
RExplain why a carbonate gives off a gas when it reacts with acid, in one sentence. Accept any sentence that says the carbonate breaks down to give carbon dioxide.
10.4

Required practical: preparing a pure, dry sample of a soluble salt

GCSE
Carry out the practical to prepare a pure, dry sample of a soluble salt, safely
Video lesson: Required practical: preparing a pure, dry sample of a soluble saltComing soon
Context. A class wants to make crystals of copper sulfate to take home. “How do we make sure there is no black copper oxide left in the crystals?” asks a pupil. The method uses an excess of the insoluble base, then filters it off, so only the soluble salt is left.

To make a pure, dry sample of a soluble salt, use an acid and an insoluble base such as copper oxide. The base is added in excess, so that all the acid is used up. The excess solid is removed by filtration. Then the solution is heated to evaporate some water, and left to crystallise, so crystals of the salt form as it cools. The crystals are dried on filter paper.

1. add excess copper oxide to warm dilute sulfuric acid2. filter off the excess solid3. heat the solution to evaporate some water4. leave to crystallise, then dry the crystals
The four steps of the practical

Try it (with your teacher). Practical: prepare copper sulfate crystals. Use dilute sulfuric acid and copper oxide only. Wear goggles and gloves, and keep the acid away from your skin and eyes. Warm the acid gently, using a water bath or a low flame under your teacher’s direction. Stop heating before the solution is dry, so that crystals can form as it cools. Do not heat the crystals strongly. Wash your hands when finished. Copper oxide and copper sulfate are harmful: put waste in the labelled container.

Key ideas

  • Use an excess of insoluble base so that all the acid is used up.
  • Filter to remove the excess solid base.
  • Evaporate some of the water, then leave the solution to crystallise.
  • Dry the crystals between filter paper; do not heat them strongly.
Worked example 10.4.1
Why is copper oxide added in excess? Write one reason.

Method. Think about the acid.

  1. Look. An excess of solid makes sure all the acid reacts.
    all acid used
  2. Conclude. So no acid is left in the salt solution.
    no acid left
  3. Write the answer.
    so that all the acid reacts

Check. The excess solid is removed by filtering. ✓

Worked example 10.4.2
Why is the solution filtered after the reaction? Write one reason.

Method. Think about what is in the mixture.

  1. Look. The mixture contains the salt solution and the excess solid.
    solid present
  2. Conclude. Filtering removes the solid, so only the salt solution passes through.
    solution passes
  3. Write the answer.
    to remove the excess insoluble copper oxide

Check. The filtrate is the salt solution. ✓

Worked example 10.4.3
Why is the solution heated only until some water has gone, not until it is dry? Write one reason.

Method. Think about the crystals.

  1. Look. Heating to dryness would give a solid mass, not crystals.
    dry
  2. Conclude. Crystals form as the solution cools, so stop when it is nearly saturated.
    crystals form
  3. Write the answer.
    so that crystals form as the solution cools

Check. Saturated means no more salt will dissolve. ✓

Watch out

Watch out: the excess copper oxide is not a mistake. It is there to use up all the acid. Filter it off; do not leave it in the crystals.

Exam tip

Exam tip. Name the four steps in order: excess, filter, evaporate, crystallise and dry. Give one reason for each.

Exercise 10D  Required practical: preparing a pure, dry sample of a soluble salt

1
FWhat is the first step in making copper sulfate from copper oxide and sulfuric acid? Write the words.
2
FWhich step removes the excess copper oxide? Write the word.
3
FWhat is the name for the solution left after filtering? Write the word.
4
FWhich process forms crystals as the solution cools? Write the word.
5
FWhat colour are copper sulfate crystals? Write the colour.
6
FWhich piece of safety equipment must be worn in the practical? Write the name. Accept goggles.
7
PSWhy must the crystals not be heated strongly? Write one reason.
8
PSWhy is excess copper oxide used, not just the exact amount needed? Write one reason.
9
RExplain why the solution is not evaporated to dryness, in one sentence. Accept any sentence that says crystals form as the solution cools, and drying to dryness may decompose the salt.
10
RA pupil says “we should filter the solution before adding the acid.” Explain why this is wrong, in one sentence. Accept any sentence that says the copper oxide must react with the acid first, and then the excess solid is filtered off.
10.5

Strong and weak acids, concentration and titration [H]

GCSE
Explain the difference between strong and weak acids, and between strength and concentration, [H] Use titration results to calculate a concentration
Video lesson: Strong and weak acids, concentration and titration [H]Coming soon
Context. A pupil says that a concentrated acid is always strong. “But my weak acid solution is concentrated,” says another pupil. Strength and concentration are different things, and titration is the method used to find a concentration precisely.

Strength describes how far an acid ionises (releases H+ ions) in water: a strong acid ionises completely, a weak acid only partly. Concentration is the amount of acid in a given volume. A concentrated weak acid can still be weaker than a dilute strong acid.

In a titration, a solution of known concentration is used to find the concentration of another solution, by finding the volume that just neutralises it. An indicator shows the end point.

[H] Higher tier only. Titration: moles of acid or alkali are found from the concentration and the volume (moles = concentration x volume in dm3). The ratio from the balanced equation then gives the moles of the other reactant, and its concentration = moles / volume (dm3).

QuantityWorkingAnswer
moles of NaOH0.10 x 25.0 / 10000.0025 mol
moles of HCl (1 : 1)same as NaOH0.0025 mol
concentration of HCl0.0025 / (20.0 / 1000)0.125 mol/dm3
A worked titration: 25.0 cm3 of 0.10 mol/dm3 NaOH is neutralised by 20.0 cm3 of HCl

Key ideas

  • Strong acid: ionises completely. Weak acid: ionises only partly.
  • Concentration: the amount of acid per volume; strength: how much it ionises.
  • Titration uses a known concentration to find an unknown one.
  • [H] Use moles = concentration x volume (dm3) and the equation ratio.
Worked example 10.5.1
Hydrochloric acid is a strong acid. Is it the same as a concentrated solution of ethanoic acid? Write yes or no.

Method. Compare strength and concentration.

  1. Strength. Hydrochloric acid is a strong acid, which ionises completely.
    strong
  2. Concentration. A concentrated solution has a lot of acid per volume; ethanoic acid is weak.
    weak
  3. Decide. They are different properties, so the answer is no.
    no
  4. Write the answer.
    no

Check. Strength is about ionisation; concentration is about amount. ✓

Worked example 10.5.2
[H] 25.0 cm3 of 0.10 mol/dm3 NaOH is neutralised by 20.0 cm3 of HCl. What is the concentration of the HCl, in mol/dm3? Write the number.

Method. Find the moles of NaOH, then use the 1 : 1 ratio.

  1. Moles. moles of NaOH = 0.10 x 25.0 / 1000 = 0.0025 mol.
    0.0025
  2. Ratio. NaOH + HCl is 1 : 1, so 0.0025 mol HCl.
    0.0025 mol
  3. Concentration. concentration = 0.0025 / (20.0 / 1000) = 0.125 mol/dm3.
    0.125
  4. Write the answer.
    0.125

Check. 0.125 x 0.0200 = 0.0025 mol. ✓

Worked example 10.5.3
[H] Does a titration use a known or unknown concentration? Write the word.

Method. Recall how titration works.

  1. Recall. One solution has a known concentration, and it is used to find the unknown one.
    known
  2. Decide. So the known concentration is used.
    known
  3. Write the answer.
    known

Check. An indicator shows the end point. ✓

Watch out

Watch out: the acid strength is not the same as its concentration. Do not say a weak acid is “dilute” in place of “weak”.

Exam tip

Exam tip. In a titration calculation, write the moles first, then the ratio, then the concentration. Keep the volume in dm3.

Exercise 10E  Strong and weak acids, concentration and titration [H]

1
FIs hydrochloric acid a strong or weak acid? Write the word.
2
FIs ethanoic acid a strong or weak acid? Write the word.
3
FDoes a strong acid always have a high concentration? Write yes or no.
4
FWhat does the word “concentration” mean for an acid? Write the words.
5
FWhat is a titration used for? Write the words.
6
FWhat is the name of the point in a titration where the indicator changes colour? Write the words.
7
PS[H] How many moles of NaOH are in 25.0 cm3 of 0.10 mol/dm3 NaOH? Write the number.
8
PS[H] A titration uses 0.0025 mol NaOH to neutralise 20.0 cm3 of HCl. What is the concentration of the HCl? Write the number in mol/dm3.
9
PS[H] In a titration, 0.0025 mol H2SO4 reacts with NaOH in a 1 : 2 ratio. How many moles of NaOH react? Write the number.
10
PS[H] A 0.10 mol/dm3 solution of NaOH is used in a titration with 25.0 cm3. Find the moles of NaOH. Write the number.
11
R[H] Explain why a titration needs an indicator, in one sentence. Accept any sentence that says the indicator shows when the acid and alkali are exactly neutralised.
12
RExplain why a dilute solution of a strong acid can have the same pH as a concentrated solution of a weak acid, or not. Write one sentence. Accept any sentence that says pH depends on the H+ concentration, not on the acid name.

Chapter summary

SkillMethod
pH scaleBelow 7 acidic; 7 neutral; above 7 alkaline. Universal indicator shows the scale.
Acids and alkalisAcids give H+ ions; alkalis give OH- ions.
NeutralisationAcid + base -> salt + water; H+ + OH- -> H2O.
SaltsMetal first; sulfate, chloride or nitrate depending on the acid.
Making a soluble saltExcess base, filter, evaporate, crystallise, dry.
Strength and concentrationStrength = how completely an acid ionises; concentration = amount per volume.
[H] TitrationMoles = concentration x volume (dm3); use the ratio, then divide by the volume.

Can you…?

  • I can use the pH scale and indicators to classify solutions
  • I can describe acids and alkalis by their ions
  • I can write word equations for neutralisation and name the salts
  • I can describe each step of making a pure, dry sample of a soluble salt, safely
  • I can explain strength and concentration, and describe titration
  • [H] I can calculate a concentration from titration results

Key terms

acid
a substance that produces H+ ions in aqueous solution
alkali
a soluble base that produces OH- ions in aqueous solution
base
a substance that neutralises an acid
neutralisation
the reaction of an acid with a base to form a salt and water
salt
the compound formed when the hydrogen of an acid is replaced by a metal
indicator
a substance that changes colour with pH
titration
a method of finding the concentration of one solution using another of known concentration
end point
the point in a titration where the indicator changes colour

Exercise 10Z  Check-up

1
Name the salt made from sulfuric acid and zinc oxide. Write the name.
2
What gas is made when calcium carbonate reacts with dilute acid? Write the name.
3
What is the pH of a neutral solution? Write the number.
4
What colour is litmus in an acid? Write the colour.
5
Write the ionic equation for neutralisation, using H+ and OH-. Write the product as the formula.
6
Name the salt made from nitric acid and potassium hydroxide. Write the name.
7
Why is the excess copper oxide filtered off? Write one reason.
8
What is the name of the process that removes water to form crystals from a solution? Write the word.
9
[H] What is the concentration of 0.0025 mol of HCl in 0.02 dm3? Write the number in mol/dm3.
10
Explain why magnesium carbonate reacts faster with acid than with water, in one sentence. Accept any answer that says the acid is needed; water does not neutralise the carbonate.

Total 20 marks. Allow about 20 minutes.

Exercise 10X  Exam-style questions

1
FName the salt made when hydrochloric acid reacts with copper oxide. Write the name.[1 mark]
2
FWrite the word equation for sulfuric acid reacting with sodium hydroxide. Write the products.[2 marks]
3
FWhat is the pH of a solution that turns universal indicator green? Write the number.[1 mark]
4
FDescribe the steps for making a pure, dry sample of copper sulfate from copper oxide and dilute sulfuric acid. Write three steps in order.[3 marks]
5
RExplain why an excess of copper oxide is used in the preparation of copper sulfate, in one sentence. Accept any sentence that says it makes sure all the acid reacts.[2 marks]
6
RExplain the difference between a strong acid and a concentrated acid, in one or two sentences. Accept any answer that says strength is how completely the acid ionises, and concentration is the amount per volume.[3 marks]
7
PS[H] 20.0 cm3 of 0.20 mol/dm3 NaOH is neutralised by 25.0 cm3 of HCl. Find the concentration of the HCl in mol/dm3. Write the number, to 3 significant figures.[3 marks]
8
PS[H] A titration of 25.0 cm3 of an acid with 0.10 mol/dm3 NaOH uses 25.0 cm3 of NaOH. What are the moles of NaOH used? Write the number.[2 marks]
9
FName the process that uses an indicator to show when an acid and an alkali are exactly neutralised. Write the word.[1 mark]
10
RExplain why neutralisation of an acid by a metal carbonate gives off a gas, in one sentence. Accept any sentence that says carbon dioxide is released when the carbonate reacts with the acid.[2 marks]
← Chapter 9: Concentration of solutionsChapter 11: Electrolysis and oxidation and reduction →

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