Question 17. Identify the correctly matched conjugate acid-base pair from this r

Question

Question 17. Identify the correctly matched conjugate acid-base pair from this reaction. H_2 0(l) + HP0^2- _4 (a q ) implies H_2PO^- _4(a q) + OH^-(a q) HPO^2- _4 is an acid and H_2 PO^- _4 is its conjugate base. H^2O is an acid and OH^- is its conjugate base. HPO_4 ^2- is an acid and H_2O is its conjugate base. H_2O is an acid and HPO_4^2-is its conjugate base. HPO_4 ^2- is an acid and OH^- is its conjugate base. A buffer made from equal amounts of nitrous acid and nitrite ion (HNO_2, NO_2) has a buffer capacity of 0.050 mol/L. If 0.035 mol of HCI is added to 150 m L of the buffer solution, what will happen to the pH? (Assume the total buffer + acid volume is still close to 150 m L) The pH will be slightly more basic. The pH will be slightly more acidic. The pH will remain exactly the same. The pH will become very acidic. The pH will become very basic.

Explanation / Answer

17

if this is an acidic buffer, i.e., a buffer made from a weak acid

then

adddition of H+ ions, in this case from HCl

will shift:

H+ + NO2- ---> HNO2

[HNO2] = increases

[NO2-] = decreases

according to henderson /buffer equation

pH = pKa + log([NO-2]/[HNO2])

then

log decreases, becomes negative, so pH decreases

it becomes more acidic

choose B

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