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Chemistry > Elements of the sea > Flashcards

Elements of the sea Flashcards

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1
Q

What is atom economy?

A

A measure of the efficiency of a reaction, calculated as (relative mass of desired product(s) ÷ relative mass of all reactants) × 100.

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2
Q

What does a high atom economy indicate?

A

Less waste is produced.

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3
Q

What happens during the electrolysis of a halide solution?

A

Halogen is released at the anode and hydrogen gas at the cathode.

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4
Q

What is the reaction at the anode for extracting bromine from brine?

A

2Br⁻(aq) → Br₂(aq) + 2e⁻.

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5
Q

What is the reaction at the cathode for extracting bromine from brine?

A

2H⁺(aq) + 2e⁻ → H₂(g).

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6
Q

Why must brine be concentrated during electrolysis?

A

If dilute, OH⁻ ions lose electrons, forming O₂ and water instead of halogen gas.

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7
Q

How are bromine and iodine displaced from brine?

A

By bubbling chlorine gas through the solution, as chlorine is more reactive.

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8
Q

What is electrolysis?

A

The use of electrical current to break down a compound into its elements.

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9
Q

What are the electrodes in electrolysis typically made of?

A

Inert substances like carbon or platinum.

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10
Q

What is the role of the anode and cathode in electrolysis?

A

Anode is positive, cathode is negative.

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11
Q

What happens to anions in electrolysis?

A

They move to the anode and lose electrons (oxidation).

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12
Q

What happens to cations in electrolysis?

A

They move to the cathode and gain electrons (reduction).

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13
Q

What determines whether a metal or hydrogen forms at the cathode in aqueous electrolysis?

A

If the metal is less reactive than hydrogen, the metal forms; otherwise, hydrogen gas forms.

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14
Q

What forms at the anode in aqueous electrolysis?

A

Oxygen gas from OH⁻ ions unless the solution contains concentrated halides, in which case halogen gas forms.

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15
Q

What is oxidation?

A

The loss of electrons.

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16
Q

What is reduction?

A

The gain of electrons.

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17
Q

What does OILRIG stand for?

A

Oxidation Is Loss, Reduction Is Gain.

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18
Q

What is an oxidising agent?

A

A substance that gains electrons and is reduced.

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19
Q

What is a reducing agent?

A

A substance that donates electrons and is oxidised.

20
Q

What are redox reactions?

A

Reactions where oxidation and reduction occur simultaneously.

21
Q

What is oxidation state?

A

The number of electrons an atom has gained or lost to form a bond or ion.

22
Q

What is the oxidation state of oxygen in most compounds?

A

-2, except in peroxides (-1) or with fluorine (+2).

23
Q

What is the oxidation state of hydrogen in most compounds?

A

+1, except in metal hydrides (-1).

24
Q

What is the oxidation state of group 1 and group 2 elements?

A

+1 and +2, respectively.

25
Q

How can you identify oxidation and reduction in a reaction?

A

Track changes in oxidation states; an increase indicates oxidation, a decrease indicates reduction.

26
Q

What are iodine-thiosulfate titrations used for?

A

To determine the concentration of an oxidising agent.

27
Q

What is the reaction between iodine and sodium thiosulfate?

A

I₂(aq) + 2S₂O₃²⁻(aq) → 2I⁻(aq) + S₄O₆²⁻(aq).

28
Q

What is the indicator used in iodine-thiosulfate titrations?

A

Starch, turning blue-black in the presence of iodine.

29
Q

What is the formula for atom economy?

A

(Relative mass of desired product ÷ Relative mass of all reactants) × 100.

30
Q

What are the trends in halogen properties down group 7?

A

Higher melting/boiling points, less volatility, and decreased reactivity.

31
Q

Why does fluorine have the highest reactivity among halogens?

A

Small atomic radius and strong attraction between nucleus and outer electrons.

32
Q

What happens when chlorine reacts with potassium iodide solution?

A

Iodine is produced: Cl₂(aq) + 2I⁻(aq) → 2Cl⁻(aq) + I₂(aq).

33
Q

What are the colours of aqueous halogens?

A

Chlorine: colourless, Bromine: orange, Iodine: brown.

34
Q

What is the test for halide ions using silver nitrate?

A

Add silver nitrate after nitric acid. Ag⁺ reacts with halide ions to form precipitates.

35
Q

What colours do silver halide precipitates show?

A

AgCl: white, AgBr: cream, AgI: yellow.

36
Q

Which silver halide dissolves in dilute ammonia?

A

Silver chloride (AgCl).

37
Q

What is the reaction at the cathode for aqueous ZnCl₂ electrolysis?

A

Zn²⁺(aq) + 2e⁻ → Zn(s).

38
Q

What is dynamic equilibrium?

A

A state where the forward and reverse reactions occur at the same rate, keeping concentrations constant.

39
Q

What does Kc indicate about equilibrium?

A

Kc > 1 means equilibrium favours products; Kc < 1 means it favours reactants.

40
Q

What is the effect of increased pressure on gas equilibria?

A

Shifts equilibrium towards the side with fewer moles of gas.

41
Q

What is the effect of increased temperature on equilibria?

A

Shifts equilibrium in the endothermic direction.

42
Q

What is the preparation method for hydrogen halides?

A

React ionic halides with concentrated acids like phosphoric acid.

43
Q

How do hydrogen halides react with water?

A

They dissociate to form strong acids, except HF, which only partially dissociates.

44
Q

What is the use of chlorine in water treatment?

A

Kills bacteria and pathogens, sterilising the water.

45
Q

What is the equilibrium constant formula?

A

Kc = [products]ᶜ × [products]ᵈ ÷ [reactants]ᵃ × [reactants]ᵇ.

46
Q

What are the safety concerns when transporting chlorine?

A

Chlorine is toxic, corrosive, and an oxidising agent, requiring pressurised containers.

Chemistry (8 decks)

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