CGP EXAM QUESTIONS: ES Flashcards by hubooshi Abduljhbar

Two carbon electrodes are placed into molten copper chloride and the power supply is turned on.

What would you see happening at the anode? Explain your answer.

At the anode, you would see bubbles of gas appearing
because chloride ions are losing electrons to form chlorine

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Two carbon electrodes are placed into molten copper chloride and the power supply is turned on.

What would you see happening at the cathode? Explain your answer.

At the cathode, you would see the elctrode being plated
because copper ions are gaining electrons to form copper metal

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A student carries out an electrolysis of dilute solution of magnesium chloride, MgCl₂_(aq)
Write the half-equation for the reaction that occurs at the cathode

2H⁺_(aq) + 2e^- –> H₂_(g)

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A student carries out an electrolysis of dilute solution of magnesium chloride, MgCl_2(aq)
Write the half-equation for the reaction that occurs at the anode

4OH^-_(aq) –> O₂_(g) + H₂O_(l) + 4e^-

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Chlorine gas is produced industrially from the electrolysis of sodium chloride solution

Name one natural source of sodium chloride

rock salt, sea water, brine

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What would you expect the student to see? Explain your answer.

The universal indicator would turn the solution blue/purple
The solution would be alkaline, because of the hydroxide ions left in solution

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Chlorine gas is produced industrially from the electrolysis of sodium chloride solution
A student carries out the electrolysis of concentrated sodium chloride solution. Once the electrolysis they add a few drops of universal indicator to the remaining solution.
Another student then carries out the electrolysis of dilute sodium chloride solution. They also add a few drops of universal indicator to the remaining solution after the electrolysis is complete.

How would the second’s students observations differ from those of the first student. Explain your answer

The universal indicator would turn the solution green
because hydrogen ions and hydroxide ions have been discharged, leaving a neutral solution of NaCl

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Chlorine gas is produced industrially from the electrolysis of sodium chloride solution
Chlorine gas can be used to displace iodine from brine

State why chlorine displaces iodine from a solution of iodide ions

Chlorine is more reactive than bromine

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Lead(II) sulfate(VI) can be made by reacting lead(II) oxide with sulfuric acid.

State the oxidation state of lead in lead(II) oxide

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Lead(II) sulfate(VI) can be made by reacting lead(II) oxide with sulfuric acid.

State the oxidation state of sulfur in lead(II) sulfate(VI)

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Chromium (Cr) can exist in a range of oxidation states.

Give the full name of the compound C₂O₃

chromium(III) oxide

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What is the formula of iron(II) nitrate(V)?

Fe(NO₃)₂

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The equation below shows the reaction of chlorine gas with iron(II) ions in solution:
Cl_2(g) + 2Fe²⁺_(aq) –> 2Cl^-_(aq) + 2Fe³⁺_(aq)

Write a half-equation to show the conversion of chlorine, Cl₂, into chloride ions, Cl^-

Cl_2(g) + 2e^- –> 2Cl^-_(aq)

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The equation below shows the reaction of chlorine gas with iron(II) ions in solution:
Cl_2(g) + 2Fe²⁺_(aq) –> 2Cl^-_(aq) + 2Fe³⁺_(aq)

Write a half-equation to show the conversion of iron(II) ions, Fe²⁺, into iron(III) ions, Fe³⁺

Fe²⁺_(aq) –> Fe³⁺_(aq) + e^-

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The equation below shows the reaction of chlorine gas with iron(II) ions in solution:
Cl_2(g) + 2Fe²⁺_(aq) –> 2Cl^-_(aq) + 2Fe³⁺_(aq)

In this reaction, which species is the reducing agent? Explain your answer

Iron(II) ions, Fe²⁺
because during the reaction they donate electrons/are oxidised

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Use oxidation states to balance this redox equation:
Ca_(s) + Al³⁺_(aq) –> Ca²⁺_(aq) + Al_(s)

3Ca_(s) + 2Al³⁺_(aq) –> 3Ca²⁺_(aq) + 2Al_(s)

10cm³ of potassium iodate(V) solution was reached with excess acidified potassium iodide solution. All of the resulting solution was titrated with 0.16 mol dm^-3 sodium thiosulfate solution.
If fully reacted with 20cm³ of the sodium thiosulfate solution

Balance the following ionic equation, showing how iodine is formed in the reaction between iodate(V) ions and iodide ions in acidic solution: IO₃^-_(aq) + I^-_(aq) + H⁺_(aq) –> I₂_(aq) + H₂O_(l)

IO₃^-_(aq) + 5I^-_(aq) + 6H⁺_(aq) –> 3I₂_(aq) + 3H₂O_(l)

How many moles of thiosulfate ions were there in 20 cm³ of the sodium thiosulfate solution?

Number of moles of thiosulfate = 0.16 x (20/1000)
= 3.2 x 10^-3 moles

In the titration, iodine reacted with sodium thiosulfate according to this equation:
I_2(aq) + 2Na₂S₂O₃_(aq) –> 2NaI_(aq) + Na₂S₄O_6(aq)

Calculate the number of moles of iodine that reacted with the sodium thiosulfate solution

2 moles of thiosulfate reacts with 1 mole of iodine, so there were (3.2 x 10^-3)/2
= 1.6 x 10^-3 moles of iodine

How many moles of iodate(V) ions produce 1 mole of iodine from potassium iodide?

1/3 = 0.33 moles

10cm³of potassium iodate(V) solution was reached with excess acidified potassium iodide solution. All of the resulting solution was titrated with 0.16 mol dm^-3 sodium thiosulfate solution.
If fully reacted with 20cm³ of the sodium thiosulfate solution

What is the concentration of the potassium iodate(V) solution?
Give your answer to an appropriate number of significant figures

There must be (1.6 x 10^-3) x 0.33 = 5.3 x 10^-4 moles of iodate(V) solution
So concentration of potassium iodate(V) = 5.3 x 10^-4 moles x (1000/10) = 0.053 mol dm^-3
(to 2 s.f)

Astatine is a halogen. It can be found below iodine in Group 7 of the periodic table

Write an ionic equation for the reaction between iodine solution and sodium astatide (NaAt)
Which substance is oxidised?

I₂ + 2At^- –> 2I^- + At₂

(sodium) astatide

A student has a sample of an aqueous potassium halide solution. She knows it contains either chloride, bromide or iodide ions. The student adds a few drops of aqueous bromine solution to the test tube and a reaction takes place.

Which halide ion is present in the potassium halide solution?

(potassium) iodide

What colour will the aqueous solution in the test tube be after the reaction has finished?

brown

A student wants to make hydrogen iodide using sodium iodide. Which of these reagents should they use? ## Footnote **A)** Hydrochloric acid **B)** Ammonia **C)** Phosphoric acid **D)** Sulfuric acid

**C)** Phosphoric acid

A sample of hydrogen bromide gas is dissolved in water to form an aqueous solution State what you would see if universal indicator was added to the solution. Explain your answer.

The solution would turn red/pink because hydrogen bromide solution is strongly acidic

A sample of hydrogen bromide gas is dissolved in water to form an aqueous solution If sulfuric acid is added to the solution, the hydrogen bromide ions reduce the sulfuric acid to sulfur dioxide. Write a full, balanced equation for this reaction

2HBr + H₂SO₄ --\> Br₂ + SO₂ + 2H₂O

Industrially, chlorine can be produced by electrolysing sodium chloride solution Describe a test you could perform to confirm that a sample of a solution contained chloride ions. Include any observations that you would see if the result of the test was positive.

Add nitric acid to the sample. Then add silver nitrate solution. If the sample contains chloride ions, white precipitate will form

Industrially, chlorine can be produced by electrolysing sodium chloride solution Explain why chlorine needs to be handled and stored extremely carefully

chlorine is toxic and corrosive, so must be kept away from skin and eyes. Chlorine irritates the respiratory system, so must not be breathed in. Chlorine is a strong oxidising agent, so it must be kept away from flammable materials

Calculate the atom economy of this reaction. Methanol is the desired product CH₃Br + NaOH --\> CH₃OH + NaBr

% atom economy = (M_r of desired product/sum of M_r of all products) x 100% = (M_r (CH₃OH) / (M_r (CH₃OH) + M_r (NaBr)) x 100% = (12.0 + (3 x 1.0) + 16.0 + 1)/((12.0 + (3 x 1.0) + 16.0 + 1) + (23.0 +79.9)) x 100% = 32.0/(32.0 + 102.9) x 100% = **23.7%**

Dichromate(VI) ions and water were mixed together and allowed to reach equilibrium at a fixed temperature: Cr₂O₇^2-_(aq) + H₂O_(l) ⇌ 2CrO₄^2-_(aq) + 2H⁺_(aq) Write an expression for K_c for this reaction

K_c = ([CrO₄^2-]²[H⁺]²) / ([Cr₂O₇^2-][H₂O])

Dichromate(VI) ions and water were mixed together and allowed to reach equilibrium at a fixed temperature: Cr₂O₇^2-(_aq) + H₂O_(l) ⇌ 2CrO₄^2-_(aq) + 2H⁺_(aq) Calculate the value of the equilibrium constant at RTP, given that the equilibrium concentrations of the reactants and products are: [Cr₂O₇^2-] = 0.20 mol dm^-3 [H₂O] = 0.60 mol dm^-3 [CrO₄^2-] = 0.10 mol dm^-3 [H⁺] = 0.30 mol dm^-3

K_c = ([0.10]²[0.30]²) / ([0.20][0.60])

Dichromate(VI) ions and water were mixed together and allowed to reach equilibrium at a fixed temperature: Cr₂O₇^2-_(aq) + H₂O_(l) ⇌ 2CrO₄^2-_(aq) + 2H⁺_(aq) What would happen to the value of K_c if the concentration of water increased? Explain your answer

There would be no change as the concentrations of the other reagents would change to keep K_c constant