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Flashcards in Elements From the Sea Deck (43)
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[ES1] How is atom economy calculated?

atom economy = (molar mass of desired product / molar mass of all products) x 100


[ES1] What are the benefits of a high atom economy?

- Less waste is produced from the reaction, which makes it cheaper.

- The reaction requires less natural resources so it is more sustainable.


[ES2] What is electrolysis?

Electrolysis is the breaking down of a substance using electrical energy.


[ES2] How is electrolysis done in the lab?

Using the following setup:

Two non-reactive electrodes are connected to the power supply and places in the solution, the power is turned on and electrolysis starts.


[ES2] How does electrolysis work?

The cations (negative ions) are attracted to the cathode and are oxidised.

The anions (positive ions) are attracted to the anode and reduced.

The compound is therefore broken up as the two ions do not need each other to be stable.


[ES2] What is a half equation?

A half equation shows the reaction that happens at the one electrode in an electrolysis reaction.

(e.g. 2Cl⁻₍ₐᵩ₎ ⇒ Cl₂ ₍ᶢ₎ + 2e⁻ )


[ES2] What are the equations for the electrolysis of NaCl solution?

Half equations:
2Cl⁻₍ₐᵩ₎ ⇒ Cl₂ ₍ᶢ₎ + 2e⁻
2H⁺₍ₐᵩ₎ + 2e⁻ ⇒ H₂₍ᶢ₎

2Cl⁻₍ₐᵩ₎ + 2H⁺₍ₐᵩ₎ ⇒ Cl₂₍ᶢ₎ + H₂₍ᶢ₎


[ES2] What is an oxidising agent?

A substance that removes electrons from other substances by accepting electrons and getting reduces.


[ES2] What is a reducing agent?

A substance that donates electrons to other substances by getting oxidised.


[ES2] What does the Roman Numeral indicate in copper(I) sulfide?

The oxidation number of copper is +1.

We can, therefore, infer that the formula for the compound is Cu₂S.


[ES2] What does the Roman Numeral indicate in sodium chlorate(I)?

The oxidation number of chlorine is +1 in the compound.

The oxidation number of oxygen and sodium do not change very often so we can assume that they are -2 and +1 respectively.

We can, therefore, infer that the formula of the compound is NaClO.


[ES3] What does chlorine look like under standard conditions?

Chlorine is a pale green gas under standard conditions.


[ES3] What does bromine look like under standard conditions?

Bromine is a red-brown liquid under standard conditions.


[ES3] What does iodine look like under standard conditions?

Iodine is a violet solid under standard conditions.


[ES3] Why does the reactivity of halogens decrease down the group?

As we go down group 7 the number of electrons shells increase, this increases the shielding from the nucleus as well as the atomic radius.

Both of these factors decrease the nuclear attraction of outer electrons, making it harder for the halogen to gain electrons.


[ES3] Why does the volatility of halogens decrease down the group?

Halogens only have intermolecular induced di-di (london) forces between their molecules.

As we move down the group the number of electrons in the halogen molecule increases.

Thus the di-di forces between the molecules become stronger, taking more energy to break.


[ES3] Why are halogens more soluble in cyclohexane than water?

Halogen molester are non-polar, so they do not solve very well in polar solvent like water, but they will dissolve readily in non-polar solvents like cyclohexanes.


[ES3] What are the results of the halogens' reaction with Ag⁺ ions?

Chlorine: white precipitate.

Bromine: creme precipitate.

Iodine: yellow precipitate.


[ES3] What are the solubilities of silver halide precipitates in ammonia?

Silver chloride: soluble in dilute ammonia.

Silver bromide: soluble only in concentrated ammonia.

Silver iodide: insluble in dilute and concentraed ammonia.


[ES3] How do halogens react with halide ions?

Less reactive halide ions are displaced.

Chlorine will displace bromine and iodide ions.
Bromine will only display iodide ions.
And iodine will not displace halide ions,

(e.g. 2Br⁻₍ₐᵩ₎ + Cl₂₍ᶢ₎ ⇒ Br₂ ₍l₎ + 2Cl⁻₍ₐᵩ₎ )


[ES3] How are hydrogen halides prepared?

X = halogen

X⁻ + H₃PO₄ ⇒ HX + H₂PO₄⁻


[ES3] How does HBr react with H₂SO₄?

2HBr + H₂SO₄ → SO₂ + Br₂ + 2H₂O


[ES3] Why is HF a weaker acid than HCl?

The F⁻ ion forms ionic bonds with the H₃O⁺ ions in solution

Which means there is an equilibrium between the bound and unbound forms of the acid.

H₃O⁺F⁻ ⇌ H₃O⁺ + F⁻


[ES5] What are some uses of chlorine?

- Sterilisation of water.

- Bleaching for use in the paper or textile industry.


[ES5] What are some risks associated with the storage and transport of chlorine?

- Chlorine is extremely toxic and can cause irreversible lung damage and eye damage upon exposure.

- Some chlorine compounds, such as those made when exposed to water, and carcinogenic.


[ES4] When is a system in dynamic equilibrium?

- When the rate of forwarding reaction is equal to the rate of reverse reaction in a reversible reaction.

- When the concentration of reactants and products remain constant.


[ES4] What is K𝒸

- An equilibrium constant provides information about the position of equilibrium.

- The magnitude of the constant indicated whether there are more reactants or more products in an equilibrium system.


[ES4] What is K𝒸 for the following reaction?
aA + bB ⇌ cC + dD

K𝒸 = [C]ᶜ [D]ᵈ / [A]ᵃ [B]ᵇ


[ES4] What happens to the equilibrium position if the temperature is increased?

The endothermic reaction is favoured, increasing the equilibrium concentration of the products of that reaction.


[ES4] What happens to the equilibrium position if the temperature is decreased?

The exothermic reaction is favoured, increasing the equilibrium concentration of the products of that reaction.