Question

Suppose, in your lab, you have run out of dilute Sulphuric acid. You require dilute $H_{2}S{O}_4$ for an important synthesis but only have concentrated Sulphuric acid, water and a glass beaker. How will you synthesize dilute $H_{2}S{O}_4$ ?

• A. By adding water slowly to the concentrated $H_{2}S{O}_4$ taken in a glass beaker and stirring continuously
• B. By adding concentrated $H_{2}S{O}_4$ to water taken in a beaker and stirring continuously
• C. Both a and b
• D. It is not feasible to prepare dilute dilute $H_{2}S{O}_4$ from concentrated $H_{2}S{O}_4$

Answer 1

The correct option is B

By adding concentrated $H_{2}S{O}_4$ to water taken in a beaker and stirring continuously

The question might look silly but it has tremendous implications. The dilution process is very exothermic. In fact, every step of the process to convert elemental Sulphur into Sulphuric acid is exothermic with the overall reaction evolving $535kJ.mo{l}^{-1}$

Which one do you think will be more violent – adding water to the acid or adding acid to the water?

It is the latter. Adding concentrated $H_{2}S{O}_4$ to water taken in a beaker slowly, while stirring throughout the process is the best way to obtain dilute $H_{2}S{O}_4$ . This offers a greater degree of control.