FlashRound Flashcards by Scarlett Davis

why, When using a chemical reactant to prepare a substance, is it desirable to have a high percentage yield?

this increases the amount of product formed

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why is a high percentage atom economy beneficial?

so that the maximum mass of reactants ends up in the desired product, minimising the amount of by-product

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give the symbol equation for the reaction between chlorine and water

Cl₂ + H₂O ⇄ HCl + HClO

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what type of reaction is the reaction between chlorine and water

disproportionation [Cl₂ is reduced to HCl (oxidation state change: 0 to -1)
Cl₂ is oxidised to HClO (hypochlorous acid) (oxidation state change: 0 to +1)]

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give the equation for the reaction between chlroine and water in bright sunlight?

2Cl2 + 2H2O -> 4H+ + 4Cl- + O2

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what colour will univeral indicator be in a solution of Cl2 and H2O?

it will first turn red due to the acidity of both reaction products (HClO and HCl) and then colourless as the HClO bleaches the colour

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what is the observation for a reaction between Cl2/Br2/Is and cold NaOH?

the colour of the halogen solution will fade to colourless

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give the equation for the reaction between chlorine and cold sodium hydroxide

Cl2(aq) + 2NaOh(aq) -> NaCl(aq) + NaClO(aq) + H2O(l)

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give the equation for the use of calcium oxide in flue gas desulphurisation

CaO(s) + 2H2O(l) + SO2(g) + 0.5O2 ⇒ CaSO4.2H2O(s)

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how does flue gas desulpharisation work?

Any gases produced by power stations are called flue gases
In desulphurisation, the acidic sulfur dioxide gas is neutralised by an alkali

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what are 2 compounds used in flue gas desulpharisation?

calcium oxide and calcium carbonate

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how is calcium oxide used in flue gas desulphurisation

A mixture of calcium oxide and water is sprayed into the flue gas which reacts to make solid calcium sulphate.

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how is calcium carbonate used in flue gas desulphurisation

The flue gas is passed through calcium carbonate, which produces solid calcium sulphate.

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give the equation for the use of calcium carbonaye in flue gas desulphurisation

CaCO3(s) + 0.5O2 + SO2 ⇒ CaSO4 + CO2

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how can the byproduct of flue gas desulphurisation be used

Solid calcium sulphate can be sold to make builders’ plaster

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how do catalytic converters work

Catalytic converters are designed to convert some of the more harmful gases present in car exhausts into less harmful ones

describe the structure of a catalytic converter

It has a honeycomb structure made of platinum and rhodium

why does a catalytic converter have a honeycomb structure

the honeycomb structure increases the effective surface area, increasing the reaction rate

what are 3 compounds removed by catalytic converters

nitrogen monoxide, carbon monoxide, unburnt hydrocarbons

give an equation for the removal of carbon monoxide using a catalytic converter

2CO + 2NO ⇒ N2 + 2CO2

give an equation for the removal of a hydrocarbon using a catalytic converter

C8H18 + 25NO ⇒ 8CO2 + 9H2O + 12.5N2

what is ozone?

a pale blue poisonous gas

where does ozone form?

the stratosphere

why is ozone essential to the survival of life on earth?

Acts as a barrier to harmful UV-B radiation; can cause skin cancer, cataracts, and plant leaf damage

how is ozone formed?

- ordinary, stable O2 is split into two by UV radiation into two oxygen atoms - one of the oxygen atoms combines with an oxygen molecule to form ozone - O2 ➡ 2O* - the quantity of ozone is maintained in a balance with oxygen, in equilibrium - O2 + O ⇌ O3

what can ozone be broken down by?

a reaction with chlorine radicals

what are Chlorofluorocarbons ?

Haloalkanes that contain both chlorine and fluorine

what were CFC's used in?

Historically used in coolants in refrigerators

why are CFC's damaging to the atmosphere?

They are damaging to the ozone layer as the breakdown of ozone can be caused be a single chlorine free-radical. This is becuase Cl* is regenerated in the final propagation step and causes a chain reaction in the decomposition of ozone

why are 'ozone-friendly' alternatives to CFC's biodegradable?

Ozone-friendly' alternatives break down rapidly in the lower atmospher as they are more reactive in comparison to CFC's

Explain why 1,1,1-trifluoroethane does not lead to the depletion of the ozone in the upper atmosphere

- 1,1,1-trifluoroethane does not contain Cl - C-F bonds are strong and do not break

what is the mechanism for the breakdown of ozone?

free radical substitution

outline the mechanism for the breakdown of ozone

- Initiation: production of a chlorine radical - CCl3F ⇒ Cl* + *CCl2F - Propagation: - Cl* + O3 ⇒ ClO* + O2 - ClO* + O3 ⇒ 2O2 + Cl*

why is the subsitution reaction between water and haloalkanes slow?

water is a poor nucleophile

how can you measure the rate of hydrolysis reactions of haloalkanes?

- add aqueous silver nitrate - the halide leaving group will combing with a silver ion to form a silver halide precipitate - the ppt only forms when the halide ion has left the haloalkane so the rate of formation of the ppt can be used to compare the reacticity of different haloalkanes

why do tertiary haloalkanes undergo a different mechanism of subsitutuiopn with hydroxide ions?

the tertiary acrbocation is stabilised by the alkyl groups around it which prevent the hydroxide ion from attacking the haloalkane in the same way as secondary and primary