Which of the following statements do you think is true when equal volumes of 1.0

Question

Which of the following statements do you think is true when equal volumes of 1.0M solutions in 1a (HCl(aq) mixed with NaOH(aq)) and 1b (NaHCO3(aq) mixed with NaOH(aq)) are mixed? Explain your reasoning.

(A) The heat corresponding to the two reactions will be equal in magnitude

(B) The amount of heat associated with the reaction in 1a is greater than the amount of heat associated with the reaction in 1b

(C) The amount of heat associated with the reaction in 1a is less than the amount of heat associated with the reaction in 1b.

Explanation / Answer

(B) The amount of heat associated with the reaction in 1a is greater than the amount of heat associated with the reaction in 1b

Reason:

In reaction (1a) both HCl and NaOH strong electrolytes which undergo complete ionisation. Hence during their neutralisation, more amount of heat is released.

But in reaction (1b), NaOH is strong base, where HCO3- is weak acid. Weak acids undergo only partial ionisation.So, some of the heat released during the neutrlisation, is utilised to ionise the weak acid. Hence net heat released in the reaction would be low.

HCO3- (aq.) + H2O (l) = H3O+ (aq.) + CO32- (aq.)

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