Chemistry, Third edition

LAND POLLUTION 421

Revision questions

22.1.A factory discharges waste containing lead ions

[Pb^2 (aq)] into a river at the rate of 10 ppm (mg dm^3 ) per

minute. Convert this rate to mol dm^3 min^1.

22.2.(i)Catalytic converters in car exhausts allow complete

oxidation of octane to occur at a low temperature. Write an

equation for this reaction.

(ii)A converter operates at 95% efficiency. How much CO 2 is

formed from the combustion of 200 g of octane?

22.3.The release of aluminium ions as a result of acid rain is

less significant in areas containing limestone rock. Why?

22.4.Carbon monoxide is a very poisonous gas. A flask of vol-

ume 1 dm^3 contains pure CO at a pressure of 1.5 atm at 298 K.

The flask is dropped and broken by a careless laboratory

worker and the gas is released into a small sealed room of

dimensions 5 m 5m 4 m which contains air at 1 atm pres-

sure and 298 K.

(i)Estimate the concentration of CO in the room in mg m^3.

(ii)Assuming that the concentration of CO is hazardous above

55 mg m^3 , will the laboratory worker be exposed to a

dangerous level of the gas?

22.5.The vapour of tetrahydrofuran (C 4 H 8 O), a solvent for

PVC, is detectable by odour alone at concentrations of

10 mg m^3 or above. What mass of the solvent would need to

be allowed to evaporate in a room of volume 100 m^3 in order to

achieve this concentration? (Assume no loss of vapour.)

22.6.A bottled water had the following analysis on its label:

Ca^2  80 ppm

Mg^2  15 ppm

K 4 ppm

Na 6 ppm

SO 42  85 ppm

(i)If the volume of the bottle was 1.25 L, how many grams of

Mg^2 did it contain?

(ii)What is the concentration of sulfate in the bottle, in units of

mol dm^3? (Remember that 1 L 1dm^3 .)

22.7.Acid pollution causes the pH of a lake to increase from

8.40 to 8.10. By how much has the [H+(aq)] increased?

22.8.It is often asked whether or not the depleted ozone layer

could be replenished artificially, by dumping ozone from high-

flying aircraft into the stratosphere. Assess the viability

of such an operation by estimating the mass of ozone (O 3 )

that would be needed to restore the ozone concentration in

the stratosphere from 1  10 ^11 mol dm^3 to 2  10 ^11

mol dm^3. Take the volume of the stratosphere as 1  1022 dm^3.

Assuming that it costs £200 to make and transport 1 kg of O 3

into the stratosphere, what would be the cost of the operation?

Extension material to support this unit is available on our website.

Paraquat, another herbicide, is quite water soluble and has been used to destroy

marijuana crops. Paraquat poisoning can occur by skin contact, inhalation or ingestion

and large doses of the poison can damage human vital organs with fatal consequences.

3. Fungicides

Organic compounds of mercury have been used as fungicides, which are used to check

the growth of fungi. The compounds break down in soil and this has had disastrous

consequences – many human deaths in Iraq (1971–1972) resulted from the population

eating bread made from grain that had been treated with methylmercury to prevent it

being destroyed by fungus. The methylmercury cation is an example of an organo-

metallicspecies; it contains an organic group (methyl) directly bonded to a metal:

CH 3 Hg

methylmercury cation