106virang how can C,D both be true?
It is found that 0.1 M solution of three Na salts NaX,NaY,NaZ have pHs 7.0,9 and 11 respectively. Which of the following statement is/are correct ?
A. The solution which has pH 7,the conjugate and HX of X- ,must be strong.
B. The pKa of solutions NaY and NaZ are 5 and 9 respectively.
C. Acid HZ is weaker than HY.
D. Acid HY is weaker than HZ.
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12 Answers
11@ virang--pls c d options !! C and D can never be right together. :)
this q is a bit tricky but nice.
106pH of NaY = 9 while that of NaZ is 11.
So NaZ is more basic. this implies that HZ is weaker compared to HY.
NaX has pH =7 so the acid HX must be equally strong.
11ans given --- A,B,C
virang can u pls explain d option A a bit..and how u got ans A.
11I have studied that for PH 7 The conjugate acid and base both have to be strong
11yes asish C is surely right,,but m having prob wid A n B..have a try at them too..dont think ans given is wrong.
106virang:
Strong acid implies weak conjugate base and stron base implies weak conjugate acid...
This is true for all acids and bases
Take
HX + H2O --> H+ + X-
Keq = Ka = [H+][X-]/[HX]
for X- + H2O --> HX + OH-
Keq = Kb = [HX][OH-]/[X-]
multiplying
KaKb=Kw
So if the first reaction is faster, then the second one is slower
So stronger acid implies weaker conjugate base and vice-versa
24since these are salts of NaOH and HX/HY/HZ
=> st base/weak acid
now Kh=Kw/Ka
take - log both sides
=> pKh=pKw-pKa
For NaY
=> 9=14-pKa
=> pKa=5
For NaZ
pKa=3
i think option b) is wrong