A 1.00 liter solution contains 0.39 M nitrous acid and 0.51 M sodium nitrite . I

ID: 507750 • Letter: A

Question

A 1.00 liter solution contains 0.39 M nitrous acid and 0.51 M sodium nitrite.

If 0.130 moles of barium hydroxide are added to this system, indicate whether the following statements are true or false.

(Assume that the volume does not change upon the addition of barium hydroxide.)

_______TrueFalse A. The number of moles of HNO2 will decrease.

_______TrueFalse B. The number of moles of NO2- will remain the same.

_______TrueFalse C. The equilibrium concentration of H3O+ will increase.

_______TrueFalse D. The pH will increase.

_______TrueFalse E. The ratio of [HNO2] / [NO2-] will increase.

HNO2 - nitrous acid, NaNO2 --> sodium nitrite

this is a buffer, since weak acid + conjugate base are present

mol of acid = MV = 0.39

mol of conjugate = MV = 0.51

mol of OH- added = 2*0.13 = 0.26

after eraction

mol of acid = MV = 0.39-0.26 = 0.13

mol of conjugate = MV = 0.51+0.26 = 0.77

pH = pKa + log(NaNO2/HNO2)

A) HNO2 must decrese, since it reacts with the OH- from the base TRUE

B) NO2- must increase, since HNO2 +OH = H2O + NO2- is formed, this is FALSE

C) H3O+ will decreases, since OH- is added, more basic, so FALSE

d) pH must increase, since it becomes more basic, TRUE

e) the ration will decreases, since HNO2 decreases and NO2- increses, FALSE

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