Question
Question: When a substance ‘A’ reacts with water, it produces a combustible gas ‘B’ and a solution of substanc...
When a substance ‘A’ reacts with water, it produces a combustible gas ‘B’ and a solution of substance ‘C’ in water, while another substance ‘D’ reacts with solution of ‘C’ to produce the same gas B on warming while ‘D’ can produce gas ‘B’ on reaction with dilute H2SO4 at room temperature. ‘A’ imparts a deep golden yellow colour to a smokeless flame on Bunsen burner. Identify ‘A’, ‘B’, ‘C’ and ‘D’ respectively are
(A) K,H2,KOH,Al
(B) Na,H2,NaOH,Zn
(C) CaC2,C2H2,Ca(OH)2,Fe
(D) Ca,H2,Ca(OH)2,Sn
Solution
The solution to this type of question will only be obtained when we use the technique of hit and trial.
We need to see what is constant while the reaction propagates and try to fit the variable terms into the same to obtain some sensible content.
Complete step by step solution:
Considering all the options simultaneously and understanding the strategy, we can see,
1. ‘A’ reacts with water to give ‘B’ and ‘C’. This means water here is constant whereas, ‘A’, ‘B’ and ‘C’ are variables.
2. ‘B’ is a combustible gas.
3. Another substance ‘D’ reacts with ‘C’ to produce the same gas ‘B’ on warming.
4. Also ‘D’ can produce ‘B’ directly at room temperature on reaction with dil. H2SO4. Thus, dil. H2SO4 here is constant while ‘D’ and ‘B’ are variables.
5. ‘A’ imparts a deep golden yellow colour to a smokeless flame on Bunsen burner.
Considering point 5 as a specified hint.
K gives pale violet flame, Na gives intense yellow flame,CaC2 gives colourless flame whereas, Ca gives brick red flame while burning on Bunsen burner.
Thus,
Na reacts with water to give a combustible gas which is H2 and a solution of NaOH is formed.
When Zn reacts with NaOH solution, it produces the same gas i.e. H2 on warming. Also, Zn can produce H2 on reaction with dil. H2SO4 at room temperature.
Therefore,
A- Na, B- H2, C- NaOH, D- Zn.
Thus, option (B) Na,H2,NaOH,Zn is correct.
Note: All the reactions are feasible when we try every possible option. But we need to find a specific hint in the given question which is most vital and would be a key point to solve the problem.