Every time I try to submit it, it tells me to check my significant digits. Pleas

Question

Every time I try to submit it, it tells me to check my significant digits. Please help me. The pKa for A and B are given and the Ka for C is given. I have converted acid A and B pKa’s to Ka. And I have also converted acid C’a Ka to pKa. Are my answers wrong? Complete the following table, which lists information about the measured acid dissociation constants of three unknown weak acids Note: be sure each number you put in the table has the correct number of significant digits. pKa relative strength acid A 2.04 x 10 4.69 B 7.9 x 10 3.1 1 (strongest) 1.98 × 10 5.70 3 (weakest)

Explanation / Answer

when log of a number is taken, the number of digits after decimal is same as number of significant figure in number

for A:

Number of digits after decimal is 2. So, answer should have 2 significant figures

use:

pKa = -log Ka

4.69 = -log Ka

Ka = 2.0*10^-5

for B:

Number of digits after decimal is 1. So, answer should have 1 significant figures

use:

pKa = -log Ka

3.1 = -log Ka

Ka = 8*10^-4

for C:

Ka has 3 significant figures. So, pka will have 3 digits after decimal

use:

pKa = -log Ka

= -log (1.98*10^-6)

= 5.703

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