Elements of the sea Flashcards
What is atom economy?
A measure of the efficiency of a reaction, calculated as (relative mass of desired product(s) ÷ relative mass of all reactants) × 100.
What does a high atom economy indicate?
Less waste is produced.
What happens during the electrolysis of a halide solution?
Halogen is released at the anode and hydrogen gas at the cathode.
What is the reaction at the anode for extracting bromine from brine?
2Br⁻(aq) → Br₂(aq) + 2e⁻.
What is the reaction at the cathode for extracting bromine from brine?
2H⁺(aq) + 2e⁻ → H₂(g).
Why must brine be concentrated during electrolysis?
If dilute, OH⁻ ions lose electrons, forming O₂ and water instead of halogen gas.
How are bromine and iodine displaced from brine?
By bubbling chlorine gas through the solution, as chlorine is more reactive.
What is electrolysis?
The use of electrical current to break down a compound into its elements.
What are the electrodes in electrolysis typically made of?
Inert substances like carbon or platinum.
What is the role of the anode and cathode in electrolysis?
Anode is positive, cathode is negative.
What happens to anions in electrolysis?
They move to the anode and lose electrons (oxidation).
What happens to cations in electrolysis?
They move to the cathode and gain electrons (reduction).
What determines whether a metal or hydrogen forms at the cathode in aqueous electrolysis?
If the metal is less reactive than hydrogen, the metal forms; otherwise, hydrogen gas forms.
What forms at the anode in aqueous electrolysis?
Oxygen gas from OH⁻ ions unless the solution contains concentrated halides, in which case halogen gas forms.
What is oxidation?
The loss of electrons.
What is reduction?
The gain of electrons.
What does OILRIG stand for?
Oxidation Is Loss, Reduction Is Gain.
What is an oxidising agent?
A substance that gains electrons and is reduced.
What is a reducing agent?
A substance that donates electrons and is oxidised.
What are redox reactions?
Reactions where oxidation and reduction occur simultaneously.
What is oxidation state?
The number of electrons an atom has gained or lost to form a bond or ion.
What is the oxidation state of oxygen in most compounds?
-2, except in peroxides (-1) or with fluorine (+2).
What is the oxidation state of hydrogen in most compounds?
+1, except in metal hydrides (-1).
What is the oxidation state of group 1 and group 2 elements?
+1 and +2, respectively.
How can you identify oxidation and reduction in a reaction?
Track changes in oxidation states; an increase indicates oxidation, a decrease indicates reduction.
What are iodine-thiosulfate titrations used for?
To determine the concentration of an oxidising agent.
What is the reaction between iodine and sodium thiosulfate?
I₂(aq) + 2S₂O₃²⁻(aq) → 2I⁻(aq) + S₄O₆²⁻(aq).
What is the indicator used in iodine-thiosulfate titrations?
Starch, turning blue-black in the presence of iodine.
What is the formula for atom economy?
(Relative mass of desired product ÷ Relative mass of all reactants) × 100.
What are the trends in halogen properties down group 7?
Higher melting/boiling points, less volatility, and decreased reactivity.
Why does fluorine have the highest reactivity among halogens?
Small atomic radius and strong attraction between nucleus and outer electrons.
What happens when chlorine reacts with potassium iodide solution?
Iodine is produced: Cl₂(aq) + 2I⁻(aq) → 2Cl⁻(aq) + I₂(aq).
What are the colours of aqueous halogens?
Chlorine: colourless, Bromine: orange, Iodine: brown.
What is the test for halide ions using silver nitrate?
Add silver nitrate after nitric acid. Ag⁺ reacts with halide ions to form precipitates.
What colours do silver halide precipitates show?
AgCl: white, AgBr: cream, AgI: yellow.
Which silver halide dissolves in dilute ammonia?
Silver chloride (AgCl).
What is the reaction at the cathode for aqueous ZnCl₂ electrolysis?
Zn²⁺(aq) + 2e⁻ → Zn(s).
What is dynamic equilibrium?
A state where the forward and reverse reactions occur at the same rate, keeping concentrations constant.
What does Kc indicate about equilibrium?
Kc > 1 means equilibrium favours products; Kc < 1 means it favours reactants.
What is the effect of increased pressure on gas equilibria?
Shifts equilibrium towards the side with fewer moles of gas.
What is the effect of increased temperature on equilibria?
Shifts equilibrium in the endothermic direction.
What is the preparation method for hydrogen halides?
React ionic halides with concentrated acids like phosphoric acid.
How do hydrogen halides react with water?
They dissociate to form strong acids, except HF, which only partially dissociates.
What is the use of chlorine in water treatment?
Kills bacteria and pathogens, sterilising the water.
What is the equilibrium constant formula?
Kc = [products]ᶜ × [products]ᵈ ÷ [reactants]ᵃ × [reactants]ᵇ.
What are the safety concerns when transporting chlorine?
Chlorine is toxic, corrosive, and an oxidising agent, requiring pressurised containers.
