the ka values at 25 degrees celsius are given below. I will use E as x10^ for si

Question

the ka values at 25 degrees celsius are given below. I will use E as x10^ for simplification

1.8E-5

7.6E-4

1.3E-3

1.4E-3

2.2E-2

which of the following acids has a ka = 2.2E-2

a) chloroethanoic acid

b) bromoethanoic acid

c) ethanoic acid

d) iodoethanoic acid

I'm kind of lost here with this one. I know that if a conjugate base of an acid has molecules in it with stronger elelectronegativities then it makes it a stronger acid thus a larger ka value. So that makes me believe that chlorooethanoic acid is correct because it has chlorine in it which is the most electronegative of the four. I would be overjoyed with an explanation with your answer. Thanks so much.

Explanation / Answer

Ka indicates strength of acid , higher is Ka the stronger is acid .

In given four options Ka of 2.2 E-2 is highest among all which means they asked for strongest acid among given options.

A strong acid is one which easily loses H+ and the conjugate base ion formed is stabilised.

Chloroethanoic acid is ClCH2COOH

now acid dissociation reaction is given by

ClCH2COOH (aq) <---> ClCH2COO-(aq) + H+ (aq)

now ClCH2COO-   is anion and is stabilised by strong electron withdrawing group Cl. Hence conjugate anion is most stabilised here compared to other acids where we have Br , I whcih are less electronegative. Electron withdrawing groups and more electronegative lemenst stabilise anions. Hence now based on these we can say Chloroethanoci acid is strongest among all

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