Question

A one-litre flask is full of brown bromine vapour. The intensity of brown colour of vapour will not decreases appreciably on adding to the flask some
A. Pieces of marble
B. Animal charcoal powder
C. Carbon tetrachloride
D. Carbon disulphide

Answer 1

Hint: The colour of bromine vapour is brown because the colour of bromine itself is brown (\[B{{r}_{2}}\]). Now the colour of its vapour will not discharge when its bromine vapour does not react with any of the given compounds in the option. Bromine is a non-polar (non-polar covalent) molecule means its dipole moment is zero (because of the symmetrical arrangement of atoms). Always like molecules dissolve in like one so, bromine will dissolve in nonpolar molecules and discharge in colour of bromine will get noticed.

Complete Step by Step Answer:
Carbon disulphide whose molecular formula is \[C{{S}_{_{2}}}\]. Its arrangement is like both sulphide atoms (disulphide) are bonded with carbon opposite to each other. The maximum valence of carbon is four and sulphide valence is two so each two sulphides form one double bond with carbon and completes the valence of carbon and itself also. Now both double bonds will be at a maximum distance to avoid the repulsion factor and that will be at 180 degree. So, on both sides the carbon arrangement of sulphide is similar and thus, the net dipole moment is zero. So, carbon disulphide is non-polar and bromine can dissolve (non-polar), and discharge in colour will appear.

Similarly, carbon tetrachloride is nonpolar because of the symmetrical arrangement of all four chlorine atoms in the space around the carbon. This results in zero net dipole moment and non-polar character of carbon tetrachloride. So, bromine and carbon tetrachloride both are nonpolar and favour solubility with each other. Also, animal charcoal absolves the colour of bromine water and helps to decolorize bromine water.

The pieces of marble (let’s say CaCO₃) are ionic and not symmetrical or can say dipole moment is not zero because of this, marbles are somewhere polar due to this bromine vapour will not dissolve in it and thus, discharge of vapour will not take place.
This, the correct option is A.

Note: The animal charcoal is formed with the horn, blood, bones, etc. of animals. All charcoal has the property to absorb colour and also odour from substances (mostly liquid and gases) for purifying purposes. Charcoal is used for pure drinking water, sugar solution, and many others. So, when it is used with bromine water, it absorbs all the colour of bromine, and the brown colour of bromine will disappear.