Pure `H_(2)S` is prepared by the action of concentrated `HCl` on

Options

A. `FeS_(2)`
B. `FeS`
C. `Sb_(2)S_(3)`
D. `Ag_(2)S`

Answer

3

Explanation

It occurs naturally in volcanic gases and in the water of certain springs it is formed when organic matter containing `S` undergo putrefaction. Traces of the gas can be deltected in the atmosphere in Industrial areas where coal burning the prevalent .It also occurs in crude coal gas from which it is carefully removed.Very small quantites of the gas are released from the bad eggs.
it is usually prepared in the labortary by the action of dilute hydrochloric acid on ferrous sulphide in a kipp's apparatus
`FeS(s)+2H^(+)(aq.)+2Cl^(-)(aq.) rarr H_(2)S(g)+Fe^(2+)(aq.)+2Cl^(-) (aq.)`
When the gas is required intermittently(as in salt analysis), a kipp generator is often used .Teh only reactions to which this device can be applied are those which involve a solid and a liquid and which donot required heating. Its use prevents waste and minimized the escape of gas into the laboratory. The gas is washed with water to remove `HCl` fumes and can be dried with `P_(4)O_(10)`
This method only gives a pure `H_(2)S` if the `FeS` is pure,which is rarely the case as the commerical material is made by melting sulpher with iron and usually contains some free iron. Since `FeS` always contain uncombined iron which reacts with the hydrochloric acid evolving hydrogen, `H_(2)S` gas is contaminated with free hydrogen. Pure hydrogen sulphide can be obtained by passing sulphur and hydrogen over pumice at `600^(@)C` or by warming antimony sulphide with consentrated hydrochloric acid
`Sb_(2)S_(3)(s)+6HCl (aq.) rarr 3H_(2)S(g) +2SbCl_(3)`.