1. What is the PH of 0.350M CsF? 2. What is the PH of 1.50M N 2 H 5 I? 3. Which
ID: 894206 • Letter: 1
Question
1. What is the PH of 0.350M CsF?
2. What is the PH of 1.50M N2H5I?
3. Which of the following WOULD NOT be considered a buffer solution?
a. 0.1 M HC2H3O2 mixed with 0.1 M NaC2H3O2 in equal amounts.
b. 0.1 M NH3 mixed with 0.1 M NH4Cl in equal amounts.
c. 0.1 M HNO2 mixed with 0.1 M NaNO2 in equal amounts.
d. 0.1 M HNO3 mixed with 0.1 M NaNO3 in equal amounts.
e. All would be considered buffers
4. If the weak acid in a buffer system has pKa 10.5, in what pH range is the system a most effective buffer?
5. In the phosphate buffer system containing K2HPO4 and KH2PO4, what is the weak acid? What is its conjugate base?
Explanation / Answer
1. What is the PH of 0.350M CsF?
solution : it is the salt of weak acid HF and strong base CsOH. pH is more than 7 so here anion F- involve in the hydrolysis.
pKa of HF = 3.14
concentration of salt = C =0.350 M
pH = 7 + 1/2 [pKa + log C] ---------------------------------> formula
pH = 7 + 1/2 [3.14 + log 0.350]
pH = 8.34
2) What is the PH of 1.50M N2H5I?
N2H5I is the salt of weak base hydrazine N2H4 and strong acid HI
so pH < 7 . here N2H5+ involve in the hydrolysis
pKb of N2H4 = 6.07
pH = 7 - 1/2 [pKb + logC]
pH = 7 - 1/2 [6.07 + log 1.5]
pH = 3.88
3)
d. 0.1 M HNO3 mixed with 0.1 M NaNO3 in equal amounts.
it is not buffer . because HNO3 strong acid . a buffer is always mixture of weak acid and its conjugate base. but here HNO3 is strong acid . it cannot be buffer
4)
pH range of buffer always pKa + 1
so buffer range = 9.5 to 11.5
5) NaH2PO4 ---------------> weak acid
Na2HPO4 ----------------> conjugate base
explanation :
H2PO4- --------------------------> HPO4-2
weak acid conjugate base
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