Final answer:
The student needs to add 7.5 ml of 1M KOH to 100 ml of 0.1M HCOOH to achieve a ratio of [HCOO^-] = 3[HCOOH]. None of the provided options (30ml, 60ml, 90ml, 120ml) are correct, suggesting a possible error in the question or the options.
Step-by-step explanation:
The student needs to create a buffer solution where the concentration of formate ion [HCOO-] is three times that of formic acid [HCOOH]. Initially, the student has 100 ml of 0.1M HCOOH. To reach the desired concentration ratio by neutralizing some of the formic acid with KOH, they should calculate how many moles of KOH are needed.
Since the existing formic acid solution contains 0.01 moles of formic acid (100 ml of 0.1 M solution), and they want [HCOO-] = 3[HCOOH], then by neutralization with KOH, we can set up the equation: [HCOOH] - x = 3x, where x is the number of moles of HCOOH that react with KOH to form HCOO-. Solving for x, we find that x = 7.5 mmol.
Since the student is using a 1M KOH solution, they would need 7.5 ml of it to obtain the desired ratio because 1 ml of 1 M solution contains 1 mmol of solute. Given the options provided, none directly match the calculated volume needed.
However, the closest correct amount that could be selected based on the options provided would be 10 ml which is not among the choices given, indicating a potential mistake in the question or the options provided.