E) 4.24 7) If the pKa of HCHO2 is 3.74 and the pH of an HCHO2/NaCHO2 solution is
ID: 1042375 • Letter: E
Question
E) 4.24 7) If the pKa of HCHO2 is 3.74 and the pH of an HCHO2/NaCHO2 solution is 3.89, which of the following is TRUE? A) [HCHO21 [NaCHO2 B) [HCHO2]> [NaCHO2l D) [HCHO2]>>[NaCHO2 B) It is not possible to make a buffer of this pH from HCHO2 and NaCHO2. 8) Which of the following are TRUE A) A buffer is most resistant to pH change when [acid] - [conjugate base] B) An effective buffer has a [base)/[acid] ratio in the range of 10- 100. C) A buffer can not be destroyed by adding too much strong base. It can only be destroyed by adding too much strong acid. D) An effective buffer has very small absolute concentrations of acid and conjugate base. E) None of the above are true. 9) You wish to prepare an HC2H302 buffer with a pH of 424. If the pKa of is 4.74, what is the ratio of C2H302 /HC2H302 must you use? That is the ratio of base to acid A) 0.10 B) 0.32 C) 2.0 D) 2.8 E) 0.50 10) When titrating a weak monoprotic acid with NaOH at 25°C, the A) pH will be equal to 7 at the equivalence point B titration will require more moles of acid than base to reach the equivalence point. nH uill he egreater than 7 at the equivalence point. d to rrach the equivalence point.Explanation / Answer
Q-7 As we know pH = pka + log (salt / acid)
here pH > pka means log factor part is positive . this can be happan if [salt] > [acid]
so answer is C
Q-8 buffer is made to neglify the small change of addition of acid and base
but this does not means we added much acid or base
so answer is A . so log factor now zero and pH only depend on pka
E can also be option if concentration of acid or base added is not in small amounts
Q- 9 according to formula given in Q-7
assume the ratio be k
4.24 = 4.74 + log k
log k = -0.5
k = 0.316 = 0.32
anwer is B
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.