MHT CET 2016 :: Chemistry :: General questions

• Chemistry - General questions

Name the reagent that is used in leaching of gold

Answer:

Explanation:

Leaching involves the treatment  of the ore with a suitable reagent so as to make it soluble while impurities remain insoluble .Leaching of gold is done with the help of their dissolution in NACN or KCN or Cu with the help of H⁺or Fe scrap

 $4Au(s)+8CN^{-}+O_{2}(g)+2H_{2}O\rightarrow 4[Au(CN)_{2}]^{-}+4OH^{-}$

How many Faradays of electricity are required to deposit 10 g of calcium from molten calcium chloride using inert electrodes? (Molar mass of calcium=40g $mol^{-1}$)

Answer:

Explanation:

Relationship  obtained on combining Faraday's first and second laws.

$W=ZQ=\frac{E}{F}\times Q= \frac{Q}{F}\times E= \frac{Q}{F}\times \frac{N}{z}$

$=\frac{l\times t}{F}\times \frac{M}{z}$

 Here, Z= electrochemical equivalent

Q= quantity of electricity passed

M= atomic mass

z= valency of the metal

 F= one Faraday or 96500 C

Given, weight  of calcium that has to be deposited=10 g

 z of the metal ion=2

 Molecular mass of calcium =40 g mol^-1

 $W=\frac{l. T}{F}\times \frac{M}{z}; 10=\frac{l. T}{F}\times \frac{40}{2}$

$=\frac{10\times2}{40}F=IT\Rightarrow 0.5F=l.T$

Select correct statement  for thermoplastic polymer

Answer:

Explanation:

Thermoplastic polymers are linear or slightly branched polymers in which the intermolecular focus of attraction are intermediate between elastomers and fibres. These polymers soften on heating and become rigid on cooling. The process of softening, moulding and cooling can be repeated as often as desired. It is  not a cross-linked polymer

The equation that represents general  van’t Hoff equation  is

Answer:

Explanation:

 The equation that represents van't Hoff general equation $\pi =\frac{n}{V}RT$

 This equation was obtained by combining three laws.

  (i)    Boyle-van't Hoff law $\Rightarrow$  $\pi \propto C$

 If V litres of solution contains n moles of solute,

 then C=$\frac{n}{V}$

Then, $\pi V$ = constant

(ii)     Charles'-van't Hoff law $\Rightarrow$  $\pi \propto T$

$\frac{\pi}{T}$= Constant

(iii)  Avogadro- van't Hoff law $\Rightarrow$   $\pi \propto n$

where, n= number of moles of solute  per litre of solution

If 'n' represents total number of asymmetric  carbon atoms in a compound, then the possible number of optical isomers of the compound is 

Answer:

Explanation:

The number  of optical isomers depends upon the number of asymmetric  centres.If n represents total number of asymmetric  carbon atoms in a compund then possible number of optical isomers of the compound is $2^{n}$

• Chemistry - General questions