Question 27 1 pts A researcher needs to prepare a pH 5 buffer. What solutions wo

Question

Question 27 1 pts A researcher needs to prepare a pH 5 buffer. What solutions would be best? O 0.20 M lactic acid (K.-1.38 x 109 + 0.10 M hydrochloric acid 0.20 M propanoic acid (K.-1.3x 10%) + 0.10 M sodium hydroxide O 0.20 M ammonia (K.-1.8 x 10°) + 0.10 M ammonium chloride O 0.20 M boric acid (K, = 5.8 x 1010) + 0.10 M sodium borate Question 28 1 pts A buffer can maintain pH upon addition of small amounts of a strong base because O the strong base is balanced by the weak acid and conjugate base in the buffer. 0 the weak acid reacts with the strong base to make more conjugate base O the strong base has a different pH than the buffer. O small amounts of base do not drastically altve an aqueous solution's PH

Explanation / Answer

27)

A buffer is best if pH is same as pKa of acid
So,
pKa is 5

use:
pKa = -log Ka
5.0 = -log Ka
Ka = 1*10^-5

use:
Kb = Kw/Ka
Kw is dissociation constant of water whose value is 1.0*10^-14 at 25 oC
Kb = (1.0*10^-14)/Ka
Kb = (1.0*10^-14)/1*10^-5
Kb = 1*10^-9

So, we need to take a solution where Ka is 1*10^-5 or Kb is 1*10^-9

2nd option is closest

Answer: option 2

Only 1 question at a time please

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