Chemical Changes | Edexcel GCSE Chemistry, Higher tier (1CH0)
Chemical Changes
- 271 questions
- 20 subtopics
- Paper 1
- Paper 1
Chemical Changes is examined in Paper 1, Chemistry 1.
It covers acids, alkalis and the pH scale, the indicators litmus, methyl orange and phenolphthalein, hydrogen ion concentration and the pH scale, investigating pH change when neutralising an acid, dilute and concentrated, weak and strong acids, bases and alkalis, reactions of acids, and testing for hydrogen and carbon dioxide, neutralisation and its ionic equation, preparing soluble salts from insoluble and soluble reactants, preparing pure, dry copper sulfate crystals, carrying out an acid-alkali titration, solubility rules, predicting precipitates and preparing an insoluble salt, electrolytes and what electrolysis is, movement of ions and predicting the products of molten electrolysis, electrolysis with inert electrodes, writing half equations, oxidation and reduction at the electrodes, electrolysis of copper sulfate solution and investigating the electrolysis of copper sulfate.
Sample questions from Chemical Changes
Answer each one closed book first, then open the answer.
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Acids, alkalis and the pH scale
Explain why hydrogen chloride only behaves as an acid once it has dissolved in water.
Show the answer
Only in solution does it release hydrogen ions, and these ions are what make a solution acidic. -
Hydrogen ion concentration and the pH scale
The hydrogen ion concentration of a solution of pH 5 is divided by ten. Give the new pH.
Show the answer
The new pH is 6. -
Bases and alkalis
Using the definition that a base reacts with an acid to give a salt and water only, explain why a metal carbonate does not fit that definition.
Show the answer
A metal carbonate also produces carbon dioxide, so a salt and water are not the only products. -
Neutralisation and its ionic equation
Name the substance formed when hydrogen ions and hydroxide ions react together.
Show the answer
Water is formed. -
Carrying out an acid-alkali titration
Describe how a pure, dry salt is made once the volume of acid needed to neutralise the alkali is known.
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The same volumes are mixed again with no indicator, and the solution is then evaporated and crystallised. -
Predicting precipitates and preparing an insoluble salt
Describe how the precipitate is separated from the mixture when an insoluble salt is prepared.
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The mixture is filtered, and the precipitate stays in the filter paper as the residue. -
Electrolysis with inert electrodes
Name the gas formed at the anode when concentrated sodium chloride solution is electrolysed with inert electrodes.
Show the answer
Chlorine is formed at the anode. -
Oxidation and reduction at the electrodes
State which of oxidation and reduction takes place at the anode during electrolysis.
Show the answer
Oxidation takes place at the anode.
The 20 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Acids, alkalis and the pH scale | The hydrogen ions released by acids and hydroxide ions released by alkalis, the ions in sodium hydroxide and sulfuric acid solutions, and the pH values of acidic, neutral and alkaline solutions. | 13 |
| Indicators: litmus, methyl orange and phenolphthalein | The colours of litmus, methyl orange and phenolphthalein in acidic and alkaline solutions, and why litmus is less useful than phenolphthalein for finding the exact point of neutralisation. | 8 |
| Hydrogen ion concentration and the pH scale | How hydrogen and hydroxide ion concentrations affect pH, the effect of adding water to acidic and alkaline solutions, and the tenfold change in hydrogen ion concentration for each unit change in pH. | 12 |
| Investigating pH change when neutralising an acid | The apparatus, variables and pH readings when calcium hydroxide is added to hydrochloric acid, how the pH rises and levels off, the equations, why stirring and small additions matter, and presenting the results in tables and graphs. | 19 |
| Dilute and concentrated, weak and strong acids | Concentrated and dilute solutions and their units, strong and weak acids as fully and partly dissociated, and why a weak acid has a higher pH and reacts more slowly than a strong acid of the same concentration. | 16 |
| Bases and alkalis | What bases and alkalis are, metal oxides and hydroxides as bases, why a metal carbonate does not fit the definition of a base, and why every alkali is a base but insoluble bases such as copper oxide are not alkalis. | 11 |
| Reactions of acids, and testing for hydrogen and carbon dioxide | The products when acids react with metals, metal oxides, hydroxides and carbonates, naming the salts and writing their equations, choosing the acid for a nitrate, and the tests for hydrogen and carbon dioxide. | 18 |
| Neutralisation and its ionic equation | What neutralisation is, how the pH changes as alkali is added, the products of neutralising sulfuric acid, how indigestion remedies work, and the ionic equation H⁺ + OH⁻ → H₂O that explains why water always forms. | 12 |
| Preparing soluble salts from insoluble and soluble reactants | Why an excess of insoluble solid is used and filtered off, crystallising the filtrate, and why a titration and a second indicator-free mixing are needed with a soluble base. | 13 |
| Preparing pure, dry copper sulfate crystals | Reacting excess copper oxide with warm dilute sulfuric acid, the equation and colour change, filtering off the excess, concentrating over a water bath without evaporating to dryness, and crystallising and drying the crystals. | 13 |
| Carrying out an acid-alkali titration | Using a pipette, burette and phenolphthalein, adding acid drop by drop near the end point, concordant results, making a pure salt, and accuracy, precision, repeatability, random and systematic errors and the uncertainty in a mean titre. | 19 |
| Solubility rules | The solubility of sodium, potassium and ammonium salts, nitrates, chlorides, sulfates, carbonates and hydroxides, the insoluble exceptions such as silver chloride and barium sulfate, and applying the rules to particular salts. | 9 |
| Predicting precipitates and preparing an insoluble salt | Predicting which mixed solutions give a precipitate, naming silver chloride, barium sulfate, copper hydroxide and lead sulfate, and mixing, filtering, washing and drying an insoluble salt. | 16 |
| Electrolytes and what electrolysis is | What an electrolyte is and why molten or dissolved ionic compounds conduct while solids do not, electrolysis as decomposition by electrical energy, why a direct current is used, and the electrodes. | 11 |
| Movement of ions and predicting the products of molten electrolysis | The cathode and anode, cations and anions and the electrodes they move to, and predicting the metal and non-metal products when molten compounds such as zinc chloride, potassium iodide and aluminium oxide are electrolysed. | 13 |
| Electrolysis with inert electrodes | The products at each electrode when copper chloride, concentrated sodium chloride and sodium sulfate solutions, acidified water and molten lead bromide are electrolysed, why hydrogen and oxygen form instead of sodium or a sulfur gas, and the tests for chlorine and oxygen. | 15 |
| Writing half equations | Half equations for copper, hydrogen, chlorine and oxygen at the electrodes, the electrolysis of molten lead bromide and sodium chloride, and why electrons sit on opposite sides at anode and cathode. | 9 |
| Oxidation and reduction at the electrodes | Oxidation and reduction as the loss and gain of electrons, deciding whether chloride, copper and lead ions are oxidised or reduced, why the two always happen together, and why reduction occurs at the cathode and oxidation at the anode. | 12 |
| Electrolysis of copper sulfate solution | How the anode loses mass and the cathode gains it when copper sulfate solution is electrolysed with copper electrodes, why the blue colour stays, and purifying copper with an impure anode, a pure cathode and copper sulfate electrolyte. | 9 |
| Investigating the electrolysis of copper sulfate | What is seen at graphite electrodes, weighing copper electrodes before and after, how current affects the mass of copper deposited and keeping the comparison fair, hypotheses and predictions, and straight-line graphs, direct proportion and gradients. | 23 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
Edexcel GCSE Chemistry, Higher tier Active Recall Guide
Every topic, not just this one. 1,857 questions with their answers.