Question

Calculate the molar concentration of the malonic acid if 38.17 mL of 0.315 M potassium hydroxide was required to neutralize 25.0 mL of malonic acid to a phenolphthalein end point.

Answer 1

The balanced reaction of the neutralization of malonic acid (C3H4O4) with potassium hydroxide (KOH) will be:

`C_3H_4O_4+2KO_{}H\rightarrow K_2C_3H_2O_4+2H_2O`

That is to say, to neutralize a mol of Malonic acid (C3H4O4) two moles of KOH are needed.

Now, we must determine the moles present in the KOH solution, they give us the molarity of the solution. Molarity represents the moles of solute in one liter of solution. So, the moles of KOH will be:

`\begin{gathered} Mo_{}lKOH=GivenVolume*\frac{0.315molKOH_{}}{1Lsolution} \\ Mo_{}lKOH=38.17mL*(1L)/(1000mL)*\frac{0.315molKOH_{}}{1Lsolution}=0.012molKOH \end{gathered}`

We will now find the moles of the acid present using the stoichiometry of the reaction. Two moles of KOH neutralize one mole of malonic acid.

`\begin{gathered} Mo_{}lC_3H_4O_4=GivenMolKOH*(1molC_3H_4O_4)/(2molKOH) \\ Mo_{}lC_3H_4O_4=0.012molKOH*(1molC_3H_4O_4)/(2molKOH)=0.006molC_3H_4O_4 \end{gathered}`

That means that in that 25 mL of malonic acid solution there was 0.006 mol of malonic acid.

Now we are going to calculate the molar concentration (molarity) of the initial solution of malonic acid before being neutralized. We have a volume of the solution of 25 mL, therefore the molarity will be:

`\begin{gathered} \text{Molarity}=\frac{\text{Moles of solute}}{L\text{ of solution}} \\ \text{Molarity}C_3H_4O_4=(0.006molC_3H_4O_4)/(25mL)*(1000mL)/(1L)=0.24M \end{gathered}`

So, the molar concentration of the malonic acid solution will be 0.24M