a solution of weak acid of molarity 0.05 mol/dm3 is titrated against 0.1mol/dm3 NaOH, the pka = 3.67
what volume of acid would u use in ur titration?
The problem doesn't say the weak acid is monoprotic but it implies that it is by listing only one pKa.
molarity x volume = molarity x volume
0.05 x volume = 0.1 x volume
You need one of the volumes if you are to titrate to the end point. If the question is how much acid to use for the titration, I would think around 40 dm^3 of the acid because that will give about 20 cm^3 of the base and you want to keep the reading errors of the buret as low as possible. (The actual reading error is the same whether its 2 dm^3 or 20 dm^3 BUT the percent error is larger for the 2 dm^3 reading.)
To determine the volume of the weak acid needed for the titration, you need to use the concept of stoichiometry and the balanced chemical equation for the reaction between the weak acid and the sodium hydroxide (NaOH) solution.
Step 1: Write the balanced chemical equation:
For an acid-base reaction between the weak acid HA and NaOH, the balanced chemical equation would be:
HA + NaOH → H2O + NaA,
where HA represents the weak acid and NaA represents the sodium salt formed.
Step 2: Determine the stoichiometry of the reaction:
From the balanced chemical equation, you can see that one mole of HA reacts with one mole of NaOH to produce one mole of water (H2O) and one mole of NaA. Therefore, the stoichiometric ratio between the weak acid and NaOH is 1:1.
Step 3: Use the stoichiometry and concentration to find the required volume of the weak acid:
The equation for molarity is given as:
Molarity (M) = moles of solute / volume of solution (in liters).
Given:
Molarity of the weak acid (HA) = 0.05 mol/dm3,
Molarity of NaOH = 0.1 mol/dm3.
Since the stoichiometric ratio is 1:1, the number of moles of the weak acid (HA) will be equal to the number of moles of NaOH consumed during the titration.
Using the formula for molarity, we can rearrange the equation to solve for the volume of solution:
Volume of solution (in dm3) = moles of solute / molarity.
Let V be the volume of the weak acid solution required, and Moles be the number of moles of NaOH consumed during the titration.
Since Molarity = Moles / Volume,
we can rearrange the equation to solve for Moles:
Moles of NaOH = Molarity of NaOH * Volume of NaOH.
Since the stoichiometric ratio is 1:1,
Moles of HA = Moles of NaOH.
Therefore,
Moles of HA = Molarity of NaOH * Volume of NaOH.
Substituting the given values:
Moles of HA = (0.1 mol/dm3) * Volume of NaOH.
Now, we can find the volume of the weak acid solution required in dm3:
Volume of HA = Moles of HA / Molarity of HA.
Volume of HA = [(0.1 mol/dm3) * Volume of NaOH] / (0.05 mol/dm3).
Simplifying the equation:
Volume of HA = 2 * Volume of NaOH.
Therefore, to determine the volume of the weak acid solution needed for the titration, you would use twice the volume of the NaOH solution.