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Analytical Methods in Environmental Chemistry Questions and Answers

21.

Molar extinction coefficient of malondialdehyde at 532 nm is 0.155 \(\mathrm{M^{-1}cm^{-1}}\). The concentration of malondialdehyde in a solution which has absorbance of 0.31 in a 1 cm curette will be

Exam Year(s)

UGC NET - 2012,

Answer: D

By the Beer-Lambert law, \(A = \varepsilon\,c\,l\). With \(A = 0.31\), \(\varepsilon = 0.155\), \(l = 1\) cm:

\[ c = \frac{A}{\varepsilon\, l} = \frac{0.31}{0.155 \times 1} \]

\[ c = 2.0 \]

The concentration is 2.0 M in the units of the coefficient given in the question. The values 0.5 M, 1.0 M and 1.5 M do not satisfy the equation.

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22.

The molecular weight of DDT is 354.5. The quantity of DDT required to prepare one litre of 10 ppm DDT solution is

Exam Year(s)

UGC NET - 2012,

Answer: A

A 10 ppm solution in water means 10 mg of solute per litre, since 1 ppm is 1 mg per litre of dilute aqueous solution. The quantity of DDT needed for one litre is therefore 10 mg. The molecular weight (354.5) is not needed for a ppm solution, and 35.45 mg, 354.5 mg and 354.5 micrograms are the amounts for other concentrations.

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23.

Element contaminating the water body is determined and quantified by using one of the following methods :

Exam Year(s)

UGC NET - 2012,

Answer: D

A colorimeter, a spectrophotometer and an atomic absorption spectrometer can each be used to determine and quantify an element that contaminates a water body, with colour development or direct absorption of the atoms. So all the above is the answer.

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24.

In which type of chromatography four modes viz, Absorption, partition, Ion exchange and exclusion, are present ?

Exam Year(s)

UGC NET - 2012,

Answer: A

The key gives HPLC, which can be run in the four modes of adsorption, partition, ion exchange and exclusion. Liquid-liquid, ion-exchange and adsorption chromatography are each a single mode. So the type that includes all four modes is HPLC.

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25.

Which of the following techniques is most appropriate for determining crystalline structure of environmental samples ?

Exam Year(s)

UGC NET - 2012,

Answer: B

X-ray diffraction is the most appropriate technique for finding the crystalline structure of an environmental sample, since crystals diffract X-rays in a pattern that identifies the minerals present. Infrared, Raman and microspectrophotometry give information on bonds and composition and not on crystal structure. The answer is X-ray diffraction.

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26.

Match the entries in Group-I with the process parameters in Group-II :

Group-IGroup-II
(i) Clark electrode1. Dissolved Oxygen
(ii) Redox Probe2. pH
(iii) Load cell3. Liquid level
(iv) Diaphragm gauge4. Vessel pressure

Choose the correct code :
Codes :
(i) (ii) (iii) (iv)

Exam Year(s)

UGC NET - 2012,

Answer: A

The key gives the code 1 2 3 4: the Clark electrode measures dissolved oxygen, the redox probe is paired with pH, the load cell with liquid level (by weight) and the diaphragm gauge with vessel pressure. The other codes pair the Clark electrode with pH or the load cell with pressure, which is wrong. This explanation follows the official key.

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27.

Which one of the following is used to determine total organic matter by Walkley and Black method ?

Exam Year(s)

UGC NET - 2012,

Answer: C

The Walkley and Black method oxidises the organic carbon of a soil with potassium dichromate in the presence of concentrated sulphuric acid, and the unused dichromate is titrated. So the reagents are \(\mathrm{K_{2}Cr_{2}O_{7}}\) and \(\mathrm{H_{2}SO_{4}}\). Sodium thiosulphate is used in iodometric titrations, KOH and nitric acid are not the oxidant of this method.

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28.

Identify a sampling method which is not non-destructive.

Exam Year(s)

UGC NET - 2012,

Answer: A

Sub-surface coring removes a sample of soil, so it is a destructive method of sampling. Neutron probes, FTIR spectroscopy and time domain methods measure the property without removing a sample, so they are non-destructive. The question asks for the one that is not non-destructive, which is sub-surface coring.

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29.

During the determination of COD, sulphanilic acid is added, because

Exam Year(s)

UGC NET - 2013,

Answer: C

The keyed answer is that the added acid removes the nitrite interference in the COD test, which is the closest of the four statements.

Nitrite is oxidised by dichromate and would add to the measured oxygen demand, so a small amount of a sulphonic acid reagent (sulfamic acid in the standard method) is added to destroy it. The keyed wording says the nitrite is oxidised to nitrate, which is the intended point: the nitrite no longer consumes dichromate. Silver sulphate, not this acid, acts as the catalyst, and mercuric sulphate, not this acid, binds the chloride, so the other statements do not apply. The acid does not keep the mixture acidic (sulphuric acid does that) and does not react with ferrous ammonium sulphate, the titrant.

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30.

In a gas chromatography experiment, the retention factor (Rf ) values for pollutant 'A' and pollutant 'B' in a mixture of pollutants were 0.5 and 0.125, respectively. If the distance travelled by solvent front is 12 cms, the distance (in cms) travelled by pollutant 'A' and pollutant 'B' will be

Exam Year(s)

UGC NET - 2013,

Answer: A

The distance travelled by a pollutant is its Rf value multiplied by the distance travelled by the solvent front. For pollutant A this is \(0.5 \times 12 = 6\) cm, and for pollutant B it is \(0.125 \times 12 = 1.5\) cm.

\[ d = R_f \times 12 \]

So the distances are 6 and 1.5 cm, option A. Option C gives the Rf values instead of distances, option B uses 6 as 3 by an arithmetic slip, and option D swaps the two substances.

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