You're performing a titration of some acetic acid. You have reason to doubt that the grocery store is selling you vinegar at the concentration listed on the label. The label says the contents are 2.00M acetic acid. You begin performing the titration on 5mL of the acetic acid sample with 0.42M NaOH. You perform the titration and find that your indicator (phenolphthalein) turns the slightest shade of pink and determine you've added 45.7mL of the 0.42M NaOH.
What is the concentration of the acetic acid purchased from the grocery?
Acetic acid is CH3COOH which I will write as HAc. The titration equation is
HAc + NaOH ==> NaAc + H2O
mols NaOH used = M x L = 0.42 M x 0.0457 = 0.0192
mols HAc titrated = 0.0192
M HAc = mols HAc/mL HAc = 0.0192/0.005 L = 3.84 M
I'd say you got your money's worth.
Well, it looks like the grocery store might be trying to pull a fast one on you with their acetic acid! Let's break it down and figure out the actual concentration.
In the titration, you added 45.7 mL of 0.42 M NaOH to neutralize the acetic acid. This means that the moles of acetic acid and moles of NaOH must be equal, according to the balanced chemical equation.
Thus, we can set up the following equation:
Moles of acetic acid = Moles of NaOH
2.00 M (unknown volume of acetic acid) = 0.42 M x 0.0457 L
Now we can solve for the unknown concentration of acetic acid by rearranging the equation:
Unknown volume of acetic acid = (0.42 M x 0.0457 L) / 2.00 M
Plugging in the values, we find:
Unknown volume of acetic acid = (0.018414) / 2.00
Unknown volume of acetic acid = 0.00921 L
Since you measured 5 mL of the acetic acid sample, we can convert that to liters:
5 mL = 0.005 L
Now we have the volume of the acetic acid and can calculate its concentration using the equation:
Concentration = moles/volume
Concentration = 0.018414 moles / 0.005 L
Concentration = 3.68 M
So it appears that the actual concentration of the acetic acid you purchased from the grocery store is approximately 3.68 M, not 2.00 M as stated on the label. Looks like they've been playing a sneaky vinegar trick on you!
To determine the concentration of the acetic acid purchased from the grocery, you can use the equation:
M1V1 = M2V2
Where:
M1 = concentration of acetic acid (unknown)
V1 = volume of acetic acid (5 mL)
M2 = concentration of NaOH (0.42 M)
V2 = volume of NaOH used (45.7 mL)
Rearranging the equation, we have:
M1 = (M2 * V2) / V1
Substituting the values we have:
M1 = (0.42 M * 45.7 mL) / 5 mL
M1 = 3.834 M
Therefore, the concentration of the acetic acid purchased from the grocery store is approximately 3.834 M.
To find the concentration of the acetic acid purchased from the grocery store, you can use the concept of stoichiometry in the titration reaction.
The balanced chemical equation for the reaction between acetic acid (CH3COOH) and sodium hydroxide (NaOH) is:
CH3COOH + NaOH → CH3COONa + H2O
From the equation, we can see that the mole ratio between acetic acid and sodium hydroxide is 1:1.
Given:
- Volume of acetic acid sample = 5 mL
- Concentration of NaOH = 0.42 M
- Volume of NaOH used for titration = 45.7 mL = 0.0457 L
Now, let's calculate the number of moles of NaOH used (nNaOH):
nNaOH = concentration of NaOH × volume of NaOH used
= 0.42 M × 0.0457 L
≈ 0.019314 moles
Since the mole ratio between acetic acid and NaOH is 1:1, the number of moles of acetic acid (nCH3COOH) used is also 0.019314 moles.
Now, let's calculate the concentration of acetic acid using the number of moles and volume of the acetic acid sample:
nCH3COOH = concentration of CH3COOH × volume of acetic acid
0.019314 moles = concentration of CH3COOH × 0.005 L
Solving for the concentration of acetic acid:
concentration of CH3COOH = (0.019314 moles) / (0.005 L)
≈ 3.863 M
Therefore, the concentration of the acetic acid purchased from the grocery store is approximately 3.863 M, which is different from the labeled concentration of 2.00 M.