complete the following table, which lists information about the measured acid dissociation constants of…
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. acid ka pka relative strength a 4.4×10^(-8) (choose one) b 1.15×10^(-8) (choose one) c 5.6 (choose one)
Answer
Explanation:
Step1: Recall the formula for $pK_a$
$pK_a = -\log_{10}(K_a)$
Step2: Calculate $pK_a$ for acid A
$pK_a(A)=-\log_{10}(4.4\times 10^{-8})$ $pK_a(A)= 7.36$ (rounded to two decimal - places for significant - digit rules as 4.4 has two significant digits)
Step3: Calculate $pK_a$ for acid B
$pK_a(B)=-\log_{10}(1.15\times 10^{-8})$ $pK_a(B)= 7.94$ (rounded to two decimal - places as 1.15 has three significant digits)
Step4: Recall the relationship between $K_a$ and $pK_a$ to find $K_a$ for acid C
$pK_a = -\log_{10}(K_a)$, so $K_a = 10^{-pK_a}$ $K_a(C)=10^{-5.6}=2.5\times 10^{-6}$ (rounded to two significant digits)
Step5: Determine relative strength
The larger the $K_a$, the stronger the acid. Since $K_a(C)=2.5\times 10^{-6}$, $K_a(A) = 4.4\times 10^{-8}$, $K_a(B)=1.15\times 10^{-8}$, the order of acid strength is $C > A > B$.
Answer:
| acid | $K_a$ | $pK_a$ | relative strength |
|---|---|---|---|
| A | $4.4\times 10^{-8}$ | 7.36 | weaker than C, stronger than B |
| B | $1.15\times 10^{-8}$ | 7.94 | weakest |
| C | $2.5\times 10^{-6}$ | 5.6 | strongest |