Topic 4 Flashcards by Helen Fincham

What do the different colours mean on the pH scale? (3 marks)

Green (7) means neutral

The more red the indicator is (1-6) the more acidic the solution is

Conversely, the more blue or purple the indicator is (8-14) the more alkaline the solution is

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What is an indicator? (1 mark)

A dye that changes colour depending on how far above or below it is from a particular pH

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What is a neutralisation reaction? (2 marks)

A rection between acids and bases (alkali dissolved in water to form a solution)

Acid + base ⇒ salt + water

H⁺_(aq) + OH^-_(aq) ⇒ H₂O_(l)

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A student uses universal indicator or test the pH of some lemon juice. What colour would you expect the indicator to turn? (1 mark)

Red/orange

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The pH of an unknown solution is found to be 8. Is the solution acidic or alkaline? (1 mark)

Alkaline

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How do you set up titrations? (5 marks)

Using pipette and pipette filler, add a set volume of the alkali to a conical flask. Add two or three drops of indicator too
Use a funnel to fill a burette with some acid of known concentration. Make you do this below eye level so that you don’t end up spilling acid on yourself if you slip your hand
Using the burette, add the acid to the alkali a bit at a time, giving the conical flask a regular swirl. Go especially slowly when you think the end-point, which is the colour change, is about to be reached
The indicator changes colour when all the alkali has been neutralised (e.g. phenolphthalein is pink)
Record the final volume of avid in the burette and use it along with the initial reading to calculate the volume of avid used to neautralise the alkali

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How could you increase the accuracy of your titration? (3 marks)

Do several different consistent readings, labelling your first titration as a rough titration to get the approximate idea. Use the multiple readings to get a mean of your results (unless there are anomalous results, which you should ignore)

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Why is universal indicator used to estimate the pH of a solution? (1 mark)

Because it can turn a variety of colour, which all indicate a range of pH values

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How do you determine when the end-point of a titration has been reached? (1 mark)

The indicator will have changed colour

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Give two reasons why you should repeat a titration until you have consistent readings

To increase the accuracy of your result and spot any anomalous results

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What do acids produce as they ionise in water? (1 mark)

Hydrogen ions (H⁺ ions)

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Do weaker or stronger acids dissociate with more H⁺ ions and why? (2 marks)

Stronger acids because they ionise completely in water

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What is pH a measure of and how does it work? (2 marks)

pH is a measure of the concentration of H+ ions in the solution. For every decrease of 1 on of the pH scale, the concentration of H+ ions increases by a factor of 10

Factor H+ ion concentration changes by = 10^-x

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What is the difference between strong acid and concentrated acid? (2 marks)

Acid strength tells you what proportion of the acid molecules ionise in water

Concentration of an acid measure how much acid there is in a certain volume of water

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Name a strong acid (1 mark)

Sulfuric acid

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What are the formulae for how metal oxide, metal hydroxide and metal carbonate each react with acids? (3 marks)

Acid + metal oxide ⇒ salt + water

Acid + metal hydroxide ⇒ salt + water

Acid + metal carbonate ⇒ salt + water + carbon dioxide

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How do you make soluble salts using insoluble bases? (5 marks)

Pick the right acid (e.g. hydrochloric, sulfuric, nitric acid) and insoluble base (e.g. insoluble metal oxide, hydroxide, carbonate)
Gently warm the dilute acid using a Bunsen burner, then turn off the Bunsen burner
Add the insoluble base to the acid a bit at a time, until no more reacts Uou’ll know when all the acid hasbeen neutralised because, even after stirring, the excess solid will just sink to the bottom of the flask
Then filter out the excess solid to get the salt solution
Gently heat the solution using a water bath or an electric heater to evaporate some of the water, making pure and solid salt crystals. Stop heating it and leave the solution to cool down so crystals should form

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Calcium carbonate is added to hydrochloric acid. Write the word equation for the reaction that occurs ( 2marks)

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Hydrochloric acid + calcium carbonate ⇒ calcium chloride + water + carbon dioxide

What is the reactivity series? (1 marks)

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A list of metals in order of their reactivity towards other substances

Fill in the blanks:

For _____, their reactivity is determined by how easily they lose their _____ - forming _____ ions. The higher up the _____ _____ they are, the easier they form those ions

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Metals, electrons, positive, reactivity series

Place the following metals in order of most reactive to least reactive:

Calcium, Carbon, Copper, Hydrogen, Lithium, Magnesium, Iron, Sodium, Potasium, Zinc (3 marks)

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Potassium, Sodium, Lithium, Calcium, Magnesium, Carbon, Zinc, Iron, Hydrogen, Copper

How can you tell how reactive a metal is from putting it in acid? Give examples (3 marks)

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The more bubbles the metal gives off in the acid, the more reactive the metal is. Very reactive metals like potassium and sodium react explosively, however a metal like copper won’t react at all. Fairly reactive metals will react but not as violently as potassium or sodium

How else can you react the reactivity of a metal? (1 mark)

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The temperature change of the reaction with an acid or water over a set time period using mass and surface area of metal each time

Give the word equations that show a metal reacting with acid, and a metal reacting with water (2 marks)

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Acid + metal ⇒ salt + hydrogen

Metal + water ⇒ metal hydroxide + hydrogen

What are oxidation and reduction reactions? (2 marks)

Oxidation is gain of oxygen Reduction is the loss of oxygen

Give the balanced equation, including state symbols, for the reaction of sodium and water (3 marks)

2Na_(s) + 2H₂O_(l) ⇒ 2NaOH_(aq) + H_2(g)

Give balanced equations for the oxidation of magnesium to make magnesium oxide and the reduction of copper oxide to make copper (2 marks)

2Mg + O₂ ⇒ 2MgO 2CuO + C ⇒ 2Cu + CO₂

# Fill in the blanks: Metals higher than _____ in the reactivity series have to be extraced using \_\_\_\_\_, which is expensive Metals below it however can be extracted by _____ using carbon This is because _____ can only take the _____ away from metals which are _____ reactive than it (3 marks)

Carbon, electrolysis, reduction, carbon, oxygen, less

Write a balanced equation for the reduction of zinc oxidde, ZnO, by carbon, C (2 marks)

2ZnO + C ⇒ 2Zn + CO₂

A mining company tried to extract calcium from its ore by reduction with carbon. The process did not work. Explain why (1 mark)

Because calcium is more reactive than carbon, so the carbon couldn't displace the calcium in the ore

What is a redox reaction? (1 mark)

A reaction where both reduction and oxidation happen at the same time

What is a displacement reaction? (2 marks)

When a metal replaces another metal in a compound during a reaction. It only happens when the replacement metal is more reaction than the one being replaced

Write the half equations for the displacement of copper sulfate by iron (2 marks) Iron + copper sulfate ⇒ iron sulfate + copper Fe_(s) + CuSO_4(aq) ⇒ FeSO_4(aq) + Cu_(s)

Fe ⇒ Fe²⁺ + 2e^- Cu²⁺ + 2e^- ⇒ Cu

The equation for the reaction of zinc and iron sulfate is Zn_(s) + FeSO_4(aq) ⇒ ZnSO_4(aq) + Fe_(s) a) Write an ionic equation for the reaction (2 marks) b) State which species is being reduced and which is being oxidised (2 marks)

a) Zn_(s) + Fe²⁺_(aq) ⇒ Zn²⁺_(aq) + Fe_(s) b) Zn is being oxidised and Fe is being reduced

What happens during electrolysis? (6 marks)

An electrical current is passed through an electrolyte, where the ions move towards the electrode, which react, causing the compound to decompose. The positive ions in the electrolyte will move towards the cathode (-ve electrode) and gain electrodes, whereas the negative ions in the electrolyte move towards the anode (+ve electrode) and lose the electrons. Together they create a low of charge through the electrolyte as ions travel to the electrodes, gaining and losing electrodes, forming the uncharged element and discharging from the electrolyte

# Fill in the blanks: An ionic solid can't be ______ because the ions are in ______ posititions and can't move. However, the opposite is true of molten ionic ______ because the ions can move ______ and conduct ______ (5 marks)

Electrolysed, fixed, compounds, freely, electricity

When molten ionic liquids are broken up into their elements, positive metal ions are reduced to the element at the cathode, and negative non-metals are oxidised to the element at the anode. Show this in half equations (4 marks)

Pb²⁺ + 2e^- ⇒ 2Br^- ⇒ Br₂ + 2e^-

Why can you extract aluminium from its ore using electrolysis, and how? (4 marks)

When metals are too reactive to be reduced with carbon, electrolysis is used. This is the case for aluminium Aluminium has a very high melting temperature, so it's mixed with cryolite to lower the melting point, helping to extract it from the ore bauxite Because the molten mixture contains free ions, it conducts electricity, meaning the positive Al³⁺ ions are attracted to the megative electrode where they each pick up three electrons and turn into the neutral aluminium ions before sinking to the bottom of the electrolysis tank. The negative O^2- ions are attracted to the positive electrode where they each lose two electrons, combining with neutral oxygen atoms to form O₂ molecules

A student carries out electrolysis on the molten sodium chloride. What are produced at the cathode and anode? (2 marks)

At the cathode is the sodium atoms (Na) At the anode is the chlorine gas (Cl₂)

# Fill in the blanks: In \_\_\_\_\_\_solutions, as well as the ions from the ______ compound, there will be ______ ions and hydroxide ions from the water (3 marks)

Aqueous, ionic, hydrogen

When trying to discharge ions from water, what happens at the anode and cathode? (3 marks)

Anode: If OH^- ions and halide ions are present, molecules of chlorine, bromine or iodine will be formed. If no halide ions are present, then the OH^- ions are discharged and oxygen will be formed Cathode: If the metal ions form an elemental metal that is more reactive than hydrogen and H⁺ ions are present, hydrogen gas will be produced. However, if the metal ions form an elemental metal that is less reactive than hydrogen, a solid layer of the pure metal will be produced instead

What would both the half equations be for a solution of copper(II) sulfate (CuSO₄) during electrolysis? Explain why (4 marks)

Copper metal is less reactive than hydrogen, so at the cathode the, copper metal is produced and coats the electrode Cu²⁺ + 2e^- ⇒ Cu There aren't any halide ions present, so at the anode oxygen and water are produced. The oxygen can be seen as bubbles 4OH^- ⇒ O₂ + 2H₂O + 4e^-

Balance the following equations: H⁺ + e^- ⇒ H₂ Cl^- ⇒ Cl₂ + e^- (2 marks)

2H⁺ + 2e^- ⇒ H₂ 2Cl^- ⇒ Cl₂ + 2e^-

An aqueous solution of copper chloride, CuCl₂, is electolysed using einert electrodes. Give the half equations for the anode and cathode (2 marks)

Anode: 2Cl^- ⇒ Cl₂ + 2e^- Cathode: Cu²⁺+ 2e^- ⇒Cu

Topic 4 Flashcards

(44 cards)