Topic 3 - Acids, Chemical Changes & Electrolytic Processes Flashcards by Emma Jensen

A student carried out an investigation to determine the order of reactivity of 4 metals, W,X, Y and Z.
A piece of metal W was added to a test tube containing excess dilute hydrochloric acid.
This was repeated with the other metals, X, Y and Z.
In each case, the size of each piece of metal was the same.
The student recorded observations on each reaction for three minutes.
The observations obtained are shown below:

Metal W = bubbles formed quickly with some metal remaining after 3 minutes.
Metal X = a few bubbles were seen to form. The metal looked unchanged after 3 minutes.
Metal Y = bubbles formed quickly. After 3 minutes, all the metal had reacted.
Metal Z = bubbles formed quickly with no metal remaining after 3 minutes.

Least reactive → most reactive
X - W - Y - Z

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metal + sulfuric acid → metal sulfate + hydrogen
When metal Y reacts with dilute sulfuric acid, bubbles form quickly at first and then the
reaction stops.
Most of the solid metal remains.
Explain why the reaction between metal Y and excess dilute sulfuric acid stopped even though there was solid metal Y left. (2)

Metal sulphate is insoluble/coats the metal/forms a barrier (1)
Prevents further reaction of metal with acid (1)

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Explain the meaning of the term weak acid. (2)

Partially dissociated/ionised (1)
Concentration of H+ ions lower than expected (1)

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A titration is carried out to find the concentration of a solution of sodium hydroxide.
The sodium hydroxide solution is titrated with dilute sulfuric acid.
The available apparatus includes a burette, pipette, funnel, conical flask and an indicator.
State one safety precaution that must be taken when using sodium hydroxide solution and dilute sulfuric acid. (1)

Wear gloves to prevent contact with skin/safety (1)
Spectacles to prevent contact with eyes (1)

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The sodium hydroxide solution is made by dissolving 4.3 g of sodium hydroxide in water
and making the solution up to 250cm^3 with water.
Calculate the concentration of the solution in g dm^−3. (2)

1000cm^3 contains 4.3 x 1000/250 (1)
1dm^3 contains 17.1 (g/dm^3) (1)

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Write the balanced equation for the reaction of dilute sulfuric acid, H2SO4, with sodium
hydroxide. (2)

2NaOH + H2SO4 → Na2SO4 + 2H2O (2)

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

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. (2)

Acid: use measuring cylinder/pipette/burette (1)
Base: balance/scales/weigh out an amount (1)

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

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. (2)

Explain, in terms of the particles present, why the pH increases during the experiment. (2)

Starts colourless, ends pink/magenta (1)

Hydrogen ions react/are neutralised (1)
H+ concentration falls/OH- concentration rises (1)

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The reactivity of copper, magnesium and zinc was investigated.
Each metal was placed separately in dilute hydrochloric acid.
The amount of effervescence was observed. The same mass of metal was used in each experiment.
Which piece of apparatus should be used to find the mass of metal used? (1)

A a balance
B a pipette
C a stopwatch
D a thermometer

State 2 variables, apart from the mass of the metals, that should be controlled in this
investigation. (2)

Magnesium produces the most vigorous effervescence. Copper does not produce any.
Give the reason why copper does not produce any effervescence. (1)

Balance (1)

Same volume of acid (1)
Same concentration of acid (1)
Same size of metal pieces (1)
Same temperature (1)

Copper isn’t reacting/unreactive (1)

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The magnesium reacts with dilute hydrochloric acid to form magnesium chloride solution
and hydrogen gas.
Complete the equation for the reaction: (2)

Mg(s) + 2HCl(aq) → MgCl2(……..) + H2(……..)

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

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When burnt completely in air, butene forms carbon dioxide and water.
Balance the equation for this reaction: (2)
C4H8 + 6O2 → ……… CO2 + …….. H2O

C4H8 + 6O2 → 4CO2 + 4H2O (2)

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Describe the test to show that a gas is carbon dioxide. (2)

Bubble gas through limewater (1)
Limewater turns cloudy/milky (1)

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

Copper carbonate + sulfuric acid → copper sulfate + carbon dioxide + water

Complete the balanced equation for this reaction. (2)

CuCO3 + H2SO4 → CuSO4 + CO2 + H2O (2)

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The scientist John Dalton lived over 200 years ago.
Another gas that Dalton investigated was chlorine.
Chlorine gas reacts with water.
The two products are a solution of hydrogen chloride and the substance HClO.
Complete the balanced equation for this reaction, including the three missing state symbols. (3)
……. (….)+ …….. (…..) ↔ …….(…..) + HClO (aq)

Cl2(g) + H2O(l) ↔️ HCl(aq) + HClO(aq) (3)

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An acid reacts with an alkali.
Give the name of this type of reaction. (1)

Neutralisation

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Describe what you would see when some copper carbonate powder is added to a
beaker of dilute sulfuric acid. (2)

Powder disappears (1)
Bubbles/fizzing (1)
Blue solution forms (1)

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Magnesium carbonate has the formula MgCO3.
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. (1)

MgCO3 + 2HCl → ……… + H2O + CO2

MgCO3 + 2HCl → MgCl2 + H2O + CO2

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The fertiliser ammonium phosphate was made by reacting ammonia solution with dilute
phosphoric acid.
In the first step, 25 cm3 of dilute phosphoric acid was placed in a beaker.
Give the name of a piece of apparatus that could be used to measure out the 25 cm3
dilute phosphoric acid. (1)

Complete the word equation for this reaction(1)

ammonia + ………………. → ……………….

Measuring cylinder (1)

ammonia + phosphoric acid → ammonium phosphate (1)

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Some ammonium phosphate solution was made.
Describe how pure, dry crystals of ammonium phosphate are obtained from the ammonium phosphate solution. (2)

Heat the solution/leave water to evaporate (1)
Then filter off/dry the crystals formed (1)

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Describe how a sample of pure, dry sodium chloride crystals can be obtained from the
filtrate. (3)

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The word equation for the reaction between copper carbonate and dilute sulfuric acid is:
Copper carbonate + sulfuric acid → copper sulfate + carbon dioxide + water

Copper carbonate is added to the acid in the flask. It’s added one spatula measure at a time until the reaction has finished.
State two observations that would show the reaction has finished. (2)

No more bubbles/fizzing (1)
No further change in colour (1)
Copper carbonate dissolves (1)

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Apparatus is used to electrolyse sodium sulfate solution using inert electrodes.
Hydrogen is produced at the negative electrode during electrolysis.

What is the name of gas X that forms at the positive electrode? (1)

Oxygen

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State what is meant by the term electrolysis. (2)

Electricity (1)
Decomposes/electrolytes ionic compounds (1)

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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.
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. (3)

Heat solution in evaporating basin (to cool) (1)
Cool and crystallise (1)
Dry ammonium sulphate crystals (between filter papers) (1)

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Magnesium carbonate has the formula MgCO3. A student has two separate test tubes with sulfuric acid. The student adds a spatula measure of magnesium carbonate, to the 1st test tube & a piece of magnesium to the 2nd 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. (6)

magnesium carbonate: • bubbles/fizzing/effervescence magnesium carbonate gets smaller/disappears • metal carbonate + acid — metal salt + carbon dioxide + water • magnesium carbonate + sulfuric acid — magnesium sulfate + carbon dioxide + water therefore, gas is carbon dioxide • test using limewater • limewater will turn cloudy magnesium • bubbles/fizzing/effervescence metal gets smaller/disappears gas is hydrogen • metal + acid — salt + hydrogen • test gas with a lit splint, it burns with a squeaky pop • magnesium + sulfuric acid — magnesium sulfate + hydrogen

Dilute hydrochloric acid is a strong acid. Explain why dilute hydrochloric acid is described as a strong acid. (2)

Fully dissociates (1) To form H+ ions (1)

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. (1)

pH 3

potassium hydroxide + hydrochloric acid → potassium chloride + water A student carried out a titration to find the exact volume of dilute hydrochloric acid that reacted with 25.0 cm3 of potassium hydroxide solution. There were 5 steps in the titration. The steps shown are not in the correct order: step J - pour the potassium hydroxide solution into a conical flask and add a few drops of indicator to this solution. step K - fill a burette with the dilute hydrochloric acid and record the initial reading from the burette. step L - use a measuring cylinder to obtain 25 cm3 of potassium hydroxide solution step M - take a final reading from the burette and calculate the volume of the dilute hydrochloric acid reacted. step N - run the dilute hydrochloric acid from the burette into the conical flask until the indicator changes colour A student was then asked to produce a pure sample of solid potassium chloride. After finding the volume of acid reacted in step M, the student added this volume of acid to a fresh 25.0 cm3 sample of the potassium hydroxide solution. This mixture was then evaporated. Explain why this new mixture was evaporated rather than the original mixture from the titration, to produce a pure sample of solid potassium chloride. (2) Suggest a reason why the actual yield was greater than the theoretical yield. (1)

Solution from titration contains an indicator (1) Indicator would contaminate salt/therefore 2nd solution used with no indicator (1) Not all the water had been evaporated off/the potassium chloride was still wet (1)

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 100 cm3 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. (1) Give an improvement to step 4 that would produce more accurate results. (1) What is the most likely change in pH during the experiment? (1) A from 1 to 7 B from 1 to 12 C from 7 to 12 D from 12 to 1 If some methyl orange indicator is added to the acid in step 2, the mixture changes colour during the experiment. State the colour change. (1)

Wear safety goggles/gloves (1) Measure mass of solid (1) From 1 to 12 (1) From red/pink to yellow (1)

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. (1) State and explain how the pH changes as the magnesium hydroxide is added to the dilute hydrochloric acid. (4)

pH meter/pH probe (1) Increase pH (1) Until pH is above 7 (1) H+ ions react with the OH- ions (1) So the hydrogen ion concentration is reduced (1)

The hydrogen ion concentration in a solution is decreased by a factor of 10. State how the pH of this solution changes. (1)

pH increases by 1

Determine wether each of these are soluble: (3) Ammonium chloride Lithium sulfate Magnesium carbonate

Ammonium chloride - soluble Lithium sulfate - soluble Magnesium carbonate - insoluble

Barium hydroxide reacts with dilute hydrochloric acid to form barium chloride and water. Barium hydroxide is corrosive. Give one precaution that the student should take when using barium hydroxide. (1)

Safety goggles/gloves

A student wanted to investigate how the pH of the mixture changes as barium hydroxide is added to dilute hydrochloric acid. Method: step 1 - measure out 50.0 cm3 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. (1) Describe how the pH of the mixture is determined when a drop of it is placed on the universal indicator paper. (2) 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. (2)

Burette/pipette (1) Observe colour produced on universal indicator paper (1) Compare to pH scale (1) Litmus paper only shows if the solution is acidic/alkaline (1) It doesn’t show how alkaline or acidic a solution is (1)

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. (1)

Phenolphthalein/methyl orange

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. (1)

It doesn’t show sharp colour change at end point

Hydrogen is given off when magnesium reacts with acid. The hydrogen is tested by collecting the gas in a test tube and igniting it. What is the safest way to ignite the gas? (1) A add fuel to the test tube B heat the test tube with a Bunsen burner C put a lighted splint at the open end of the test tube D put the test tube in an oven

put a lighted splint at the open end of the test tube

Sodium hydroxide solution was added to a solution of copper sulfate. A precipitate of copper hydroxide and a solution of sodium sulfate were formed. State what would be seen in the reaction. (1)

Solid forms/goes cloudy

Complete the balanced equation for the reaction by adding a number in front of NaOH. (1) ..........NaOH + CuSO4 → Cu(OH)2 + Na2SO4

2NaOH + CuSO4 → Cu(OH)2 + Na2SO4

Fertilisers contain compounds that promote plant growth. State the name of an element in these compounds that promotes plant growth. (1)

Phosphorus/potassium/nitrate

Potassium nitrate is present in some fertilisers. Potassium nitrate is formed by the reaction of potassium hydroxide solution with nitric acid. Complete the balanced equation for this reaction. (2) KOH + HNO3 → .............

KOH + HNO3 → KNO3 + H2O

Aluminium oxide reacts with hydrochloric acid to form a salt and water. State the name of the salt formed. (1)

Aluminium chloride

Nitric acid can be titrated with a solution of ammonia. State the type of reaction occurring when nitric acid reacts with ammonia. (1)

Neutralisation/exothermic

Copper carbonate + sulfuric acid → copper sulfate + carbon dioxide + water A conical flask contains 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 2 observations that would show the reaction has finished. (2)

No more bubbles/fizzing (1) No further change in colour (1) No more solid copper carbonate dissolves (1)

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. (1)

The acid is in excess (1) 1/10,000 (1)

During a reaction, the pH of a mixture changed from 2 to 6. By what factor has the concentration of the hydrogen ions in the mixture changed? (1)

Water, acidified with sulfuric acid, is decomposed by electrolysis. The water is decomposed to produce hydrogen and oxygen. A sample of hydrogen is mixed with air and ignited. State what would happen. (1)

Squeaky pop/gas burns/water forms

Potassium carbonate reacts with dilute sulfuric acid to form potassium sulfate. Potassium sulfate contains potassium ions, K+, and sulfate ions. Write the formula of potassium sulfate. (1)

K2SO4

results obtained from an electrolysis experiment when copper sulfate solution was electrolysed for 10 minutes. Anode mass before 6.43, after 5.63 (-0.8) Cathode mass before 6.17, after 6.95 (+0.78) Explain, in terms of ions, the changes in mass of the two electrodes shown in the results. (3) The electrolysis was repeated using another pair of copper electrodes of the same masses. Explain a change that could be made to the electrolysis experiment to cause the mass of the cathode to increase by 2.34 g in 10 minutes.

At anode, copper atoms lose electrons (causing a decrease in mass) (1) Copper ions in solution move to cathode (1) At cathode, copper ions gain electrons (causing an increase in mass) (1) Mass of copper increased by 3 times/2.34➗0.78=3 (1) So need 3x more current/voltage flowing through solution (1)

This question is about electrolysis. A sample of molten potassium bromide is electrolysed. What are the two products formed? (1)

potassium and bromine

Molten lead bromide is electrolysed. The products of this electrolysis are (1)

lead and bromine

Apparatus is used to electrolyse sodium sulfate solution using inert electrodes. Hydrogen is produced at the negative electrode during electrolysis. What is the name of the gas that forms at the positive electrode? (1) A ammonia B oxygen C nitrogen D sulfur dioxide

Oxygen

A solution of copper sulfate in a beaker is electrolysed using copper electrodes. During the electrolysis, the anode gets smaller, the cathode gets larger and the solution remains the same shade of blue. Give the reason for each of these observations. (3)

the anode gets smaller = oxidation of copper atoms/ copper atoms become ions and go into solution (1) the cathode gets larger = reduction of copper ions/copper atoms formed from ions in solution (1) the solution remains the same shade of blue = same number of ions enter and leave the solution (1)

Before the electrolysis, the masses of the electrodes were determined. After the electrolysis, the electrodes were washed & dried & their masses re-determined. Figure 6 shows these masses and the resulting changes in masses of the electrodes. Explain these results. (4) Anode 11.27g to 10.42g - decreased by 0.85g Cathode 11.32g to 12.17g - increased by 0.85g

Anode lost copper and cathode gained copper (1) At anode copper atoms become copper ions (1) And lose 2 electrons (1) At cathode copper ions become copper atoms (1) And gain 2 electrons (1)

Molten zinc chloride is an electrolyte. Which products are formed at the anode and at the cathode when molten zinc chloride is electrolysed? (1)

Chloride at anode and zinc at cathode

Which of the following is the reason why molten zinc chloride is an electrolyte? (1) A it contains molecules that can move B it has a giant structure C it contains delocalised electrons D it contains ions that can move

it contains ions that can move

Calcium nitrate and calcium carbonate are both ionic compounds. Calcium nitrate mixed with water behaves as an electrolyte. Calcium carbonate mixed with water does not behave as an electrolyte. Explain, in terms of solubility and movement of ions, this difference in behaviour. (2)

Calcium nitrate is soluble/calcium carbonate isn’t (1) So ions free to move in solution but not in solid (1)

Impure copper can be purified using electrolysis. In this electrolysis: • the anode is made of impure copper • the cathode is made from pure copper • the electrolyte is copper sulfate solution. During the electrolysis three observations are made • the sizes of both the anode and the cathode change • a solid appears directly beneath the anode • the colour of the copper sulfate solution does not change. Explain all three observations. (6)

• copper atoms form copper ions at anode • (copper atoms are oxidised / lose electrons) • Cu Cu2+ + 2e • copper ions pass into solution • copper ions move to / are attracted by the cathode • cathode increases in size / gains mass • pink/ brown colour on the surface of the cathode • solid copper deposited on the cathode • (copper ions are reduced/gain electrons) • copper ions form copper atoms • Cu2- + 2e —> Cu • copper sulfate solution is blue colour • colour remains same since for every copper ion entering the solution at the anode, one is removed from the solution at the cathode • concentration of copper sulfate (solution) remains the same • solid is the insoluble impurities falling from the anode

Before the electrolysis is carried out, the mass of each electrode is determined. Explain what should be done to the copper electrodes before their masses are determined. (2)

Electrodes cleaned (with emery paper) (1) To remove grease/surface oxide/impurities (1)

When sodium sulfate solution is electrolysed, using inert electrodes, hydrogen is formed at the cathode. Write the half equation for the formation of hydrogen gas, H2, from hydrogen ions, H+. (2)

2H+ + 2e- → H2

Complete the balanced equation for the reaction that occurs. (1) ........................... HCl → H2 + Cl2

2HCl → H2 + Cl2

In the electrolysis of sodium chloride solution, bubbles of a colourless gas form at the cathode. This gas, when mixed with air, burns with a squeaky pop. Identify this gas. (1) Explain how this gas is formed at the cathode. (2)

Hydrogen (1) Hydrogen ions attracted to cathode (1) 2 hydrogen ions gain 2 electrons (1)

Apparatus is used to electrolyse sodium sulfate solution using inert electrodes. The gases given off at the electrodes are collected in test-tubes. However, the actual volume of gases cannot be measured using these test-tubes. Suggest what apparatus could be used in place of the test-tubes to measure the volume of gases given off. (1) State what could be added into the circuit to show a current is flowing during electrolysis. (1)

Measuring cylinder (1) Light bulb/ammeter (1)

When molten zinc chloride is electrolysed, zinc ions, Zn2+, form zinc atoms. Write the half equation for this reaction. (2)

Zn2+ + 2e- → Zn (2)

Electrolysis is also used to produce chlorine on a large scale. Name a raw material that can be electrolysed to produce chlorine. (1)

Seawater/sodium chloride solution/salt/brine

Acids are neutralised by metal hydroxides to form (1) A salt only B salt and hydrogen only C salt and oxygen only D salt and water only

salt and water only

Acids can be neutralised by metal carbonates. Dilute sulfuric acid is neutralised by copper carbonate as shown in the word equation. Copper carbonate is a green powder. Describe what you would see when copper carbonate powder is added to dilute sulfuric acid. (2) copper carbonate + sulfuric acid → copper sulfate + carbon dioxide + water

Green solid disappears/dissolves (1) Effervescence/bubbles of colourless gas given off (1) Blue solution forms (1)

Magnesium carbonate reacts with dilute nitric acid. Give the names of the products formed in this reaction. (2)

Magnesium nitrate, water and carbon dioxide

Zinc oxide, ZnO, reacts with dilute hydrochloric acid to form zinc chloride, ZnCl2, and water. This reaction is an example of (1) A combustion B thermal decomposition C neutralisation D oxidation

Neutralisation

Write the balanced equation for the reaction between zinc oxide and dilute hydrochloric acid. (3)

ZnO + 2HCl → ZnCl2 + H2O

Electrolysis of hydrochloric acid can produce hydrogen and chlorine. The apparatus for the electrolysis is - hydrochloric acid - 2 carbon rods - a suitable container for the electrolysis reaction - a suitable source of electricity - test tubes Describe how the apparatus can be used to electrolyse hydrochloric acid and how the gases produced can be tested to show that they are hydrogen and chlorine. (6)

experiment set up: • hydrochloric acid in container • carbon rods in acid • attach rods to electrical supply • d.c. supply(or reference to positive & negative) • test tubes to collect gases test hydrogen: • lighted splint • squeaky pop (with air)/burns test chlorine: • (damp blue) litmus paper • (turns red then) bleaches/white

Which of the following pairs of substances contains one substance that is soluble in water and one that is insoluble in water? (1) A aluminium nitrate and lead sulfate B ammonium chloride and copper sulfate C copper hydroxide and lead sulfate D sodium hydroxide and potassium nitrate

aluminium nitrate and lead sulfate

Barium chloride solution is used to test for the presence of sulfate ions in a solution. When sulfate ions are present, insoluble barium sulfate is formed. Describe the appearance of barium sulfate. (1)

White precipitate/solid

Complete the balanced equation for the reaction between barium chloride and potassium sulfate. (2) BaCl2 + K2SO4 →

BaCl2 + K2SO4 → BaSO4 + 2KCl

Which state symbol is used for NaCl (1)

(Aq)

Write the ionic equation for: (2) HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

H+ + OH- → H2O

When sodium hydroxide solution is titrated with dilute hydrochloric acid, an acid-base indicator is used. The hydrochloric acid is added from a burette to the sodium hydroxide solution in a conical flask. At the end point the indicator changes colour. State the colour change if methyl orange/phenolpthalein indicator were used. (2)

Methyl orange: yellow to orange/pink/red (1) Phenolphthalein: magenta/pink to colourless (1)

A sample of molten potassium bromide is electrolysed. What are the two products formed? (1) A hydrogen and oxygen B hydrogen and bromine C potassium and oxygen D potassium and bromine

potassium and bromine

Describe the test to show that a gas is chlorine. (2)

Damp red litmus paper (1) Turns red and then bleaches/goes white (1)

A reaction produces silver chloride as a precipitate. In an equation this would be shown as (1) A AgCl(aq) B AgCl(g) C AgCl(l) D AgCl(s)

AgCl(s)

Apparatus is used to investigate the mass of the reactants and the mass of products in this reaction. The total mass of this apparatus was measured. The flask was shaken to allow the silver nitrate solution and dilute hydrochloric acid to react. After the reaction the total mass of the apparatus was measured again. State how the total mass of the apparatus after the reaction will compare with the total mass of the apparatus before the reaction. (1)

No change

The ions in sodium chloride solution are sodium ions, Na+ chloride ions Cl, – hydrogen ions H, + hydroxide ions, OH– Sodium chloride solution is electrolysed using a direct electric current. Which of these ions will be attracted to the cathode during the electrolysis of sodium chloride solution? (1) A H+ ions only B H+ and Na+ ions C Cl– ions only D Cl– and OH– ions

H+ and Na+ ions

Chlorine is one of the products of the electrolysis. The half-equation for the production of chlorine is: 2Cl– → Cl2 + 2e Explain how the half-equation shows that chloride ions are oxidised. (2)

Electrons (1) have been lost (1:

Suggest why the solution remaining at the end of an electrolysis is alkaline. (1)

Contains excess hydroxide ions (1) Sodium and hydroxide ions remain (1) It’s sodium hydroxide (1) Hydrogen ions have been removed (at cathode) (1)

The electrolysis of sodium chloride solution does not produce metallic sodium. State what change you would make to the electrolyte to obtain metallic sodium. (1)

Use molten/liqid electrolyte/sodium chloride

When copper sulfate solution is electrolysed using inert electrodes, oxygen is formed at the positively charged anode. Explain how the oxygen is formed from ions in the solution. (2)

Hydroxide ions from water (1) Ions lose electrons/oxidised (1)

Duralumin is an alloy of aluminium and copper. The radii of the aluminium and copper atoms are shown: aluminium = 1.43 × 10^−12 copper = 1.27 × 10^−12 Explain why copper added to aluminium to form the alloy makes the alloy stronger than pure aluminium. (2)

Aluminium and copper have different sized atoms (1) And so this prevents the layers of metal ions from sliding over each other (1)

Which material is most suitable to make the electrodes for the electrolysis of a dilute acid? (1) A zinc B sulfur C iron D graphite

graphite

When a solution of sodium sulfate, Na2SO4, is electrolysed, the products formed at the electrodes are hydrogen and oxygen. Explain the formation of the products at the electrodes. (4)

Hydrogen and sodium ions attracted to cathode, hydroxide and sulfate ions attracted to anode (1) Because the ions are attracted to the oppositely charged electrode (1) 2 hydrogen ions (1)

Copper is purified by the electrolysis of copper sulfate solution using an impure copper anode and a pure copper cathode. Write the half-equation for the formation of a copper atom from a copper ion. (2)

Cu2+ + 2e- → Cu (2)

Water can be decomposed by electrolysis. Hydrogen and oxygen are formed. Write the balanced equation for water decomposing to form hydrogen and oxygen. (3)

2H2O → 2H2 + O2 (3)

Seawater can also be decomposed using electrolysis. Seawater is sodium chloride solution. When this is decomposed one product is a toxic gas. The toxic gas produced is: (1) A hydrogen B chlorine C oxygen D carbon monoxide Give a safety precaution that should be taken when collecting this toxic gas. (1)

Carbon monoxide (1) Use a fume cupboard/open all the windows/ventilation/wear a gas mask