1.In a titration, 50.0 mL of an acetic acid solution required 20.0 mL of a standard solution of
0.200 mol/L NaOH(aq). The concentration of the acetic acid solution is
a.
0.08 mol/L.
b.
0.50 mol/L.
c.
0.05 mol/L.
d.
1.0 mol/L.
e.
0.30 mol/L.
How do I solve this question?
To solve this question, you need to apply the concept of stoichiometry and the equation of the reaction between acetic acid (CH3COOH) and sodium hydroxide (NaOH).
The balanced equation for the reaction is:
CH3COOH(aq) + NaOH(aq) -> CH3COONa(aq) + H2O(l)
From the equation, we can see that the mole ratio between acetic acid and sodium hydroxide is 1:1. This means that the number of moles of acetic acid is equal to the number of moles of sodium hydroxide used in the reaction.
First, calculate the number of moles of sodium hydroxide used in the reaction using the formula:
moles of NaOH = concentration of NaOH x volume of NaOH
moles of NaOH = 0.200 mol/L x 0.020 L = 0.004 mol
Since the mole ratio is 1:1, the number of moles of acetic acid in the solution is also 0.004 mol.
Next, calculate the concentration of acetic acid using the formula:
concentration of acetic acid = moles of acetic acid / volume of acetic acid
concentration of acetic acid = 0.004 mol / 0.050 L = 0.08 mol/L
Therefore, the concentration of the acetic acid solution is 0.08 mol/L, which corresponds to option (a).
You do these titration questions one of two ways.
IF you know (and only if) that 1 mol acid = 1 mol base (as is true in this case), you may us mLacid x Macid = mLbase x M base. Substitue and solve for the one unnown.
If you don't know you have a 1:1 ratio, you MUST do it another way, as follows for this problem. You may want to try it both ways to see that you get the same answer both ways.
1. Write the equation. HAc is acetic acid . HAc + NaOH ==> NaAc + H2O
2. mols NaOH - M x L = ?
3. Using the coefficients in the balanced equation, convert mols NaOH to mols HAc. In this case mols HAc = mols NaOH. IF you had a titration of say H2SO4 and NaOH, then
H2SO4 + 2NaOH ==> Na2SO4 + 2H2O.
Here you would bet mols NaOH the same way (mols = M x L) but to convert to mols H2SO4, then mols H2SO4 = 1/2 mols NaOH.
4. Then, M HAc = mols HAc/L HAc = ?
Post your work if you get stuck.