Question

If you have 1000 mL of 0.1M formic acid and add 30 mmol of sodium hydroxide. What is the ratio of [formate]/[formic acid] in the final solution?

Answer 1

volume of HCOOH = 1000 ml = 1L

Moles of formic acid = M x V ( inL)   = 0.1 x 1 = 0.1 mol  

Moles of sodium hydorixde = 30 mmol = 0.03 mol = moles of OH-   ( since NaOH is strongly dissociative)

we have reaction   HCOOH + OH- <----> HCOO- (aq) + H2O (l)

Initially HCOOH moles = 0.1 , HCOO- moles = 0

after reacting with 0.03 mol of OH- , HCOOH moles = 0.1-0.03 = 0.07

[HCOOH] = moles / volume = 0.07 mol /1L = 0.07 M

moles of HCOO- formed = moles of OH- reacted = 0.03

[HCOO-] = 0.03/1 = 0.03L

now [HCOO-] /[HCOOH] = 0.03/0.07 = 0.4286