Experiment 5
CONCENTRATION OF ACIDS AND
PERCENTAGE OF ACETIC ACID IN VINEGAR
Purpose:
To determine the concentration or molarity (moles/ liter) of three acids
by neutralization with known amounts of sodium hydroxide (base).
To determine the percentage by mass of acetic acid in vinegar.
Introduction:
Acetic acid is produced by the bacterial oxidation of ethanol. Apple
cider is often the source of this ethanol. The process stops when the
concentration of acetic acid becomes large enough to prevent the
bacteria from continuing the oxidation of ethanol. The resulting solution
of acetic acid is called vinegar. In this experiment you will titrate the
acetic acid in a known mass of vinegar with sodium hydroxide solution
of a known concentration. The sodium hydroxide will neutralize the
acetic acid. Phenolphthalein is added to indicate the point at which the
acetic acid has been completely neutralized by the sodium hydroxide. A
knowledge of the concentration (moles per liter) and the volume (liters)
of the sodium hydroxide required to neutralize the acetic acid enables us
to calculate the number of moles of sodium hydroxide used. Since acetic
acid has one ionizable hydrogen atom per molecule, one mole of sodium
hydroxide will neutralize one mole of acetic acid. Hence, the number of
moles of acetic acid present in the vinegar can be obtained and used to
calculate the mass of acetic acid in the known mass of vinegar.
Experiment:
Pour enough vinegar in a beaker to cover the bottom. (10 – 15 g )
Record the mass of the vinegar.
Add 1 drop of phenolphthalein indicator solution to the flask.
Obtain about 100 cm3 of 1.00 M sodium hydroxide.
Fill the buret and fasten it to a ring stand with a buret clamp. Let some of the
sodium hydroxide solution run rapidly from the buret to expel all air
bubbles. Read the initial volume of the liquid at the level of the bottom of
the meniscus. The meniscus is the curved surface of the liquid.
Place the beaker under the buret. With continuous swirling of the flask to
ensure thorough mixing, run in the sodium hydroxide solution from the buret
until the color changes. (One drop will give you the change!) Read the final
volume of the liquid at the level of the bottom of the meniscus.
Repeat the above procedure for the other two acids.
V(NaOH)/V(Acid) = M(Acid)/M(NaOH)
M(NaOH) = 1.00moles/liter
(1) VINEGAR
NaOH + CH3COOH  NaCH3COO + H2O
Mass of Vinegar:
___________ grams (1gram = 0.001 Liters)
Volume of Vinegar:
____________liters
Initial reading of buret: _____________
Final reading of buret: _____________
Volume on NaOH used (Liters):____________
(2) Hydrochloric Acid
NaOH + HCl  NaCl + H2O
Volume of hydrochloric (HCl) acid:___________liters
Initial reading of buret:
___________
Final reading of buret:
___________
Volume on NaOH used (Liters): ___________ liters
(3) Sulfuric Acid
2NaOH + H2SO4  Na2SO4 + 2H2O
Volume of sulfuric (H2SO4) acid:_____________ liters
Initial reading of buret:
______________
Final reading of buret:
______________
Volume on NaOH used (Liters): ______________ liters
Lab Report: (To be passed in on a separate sheet.)
Purpose: What is this labs purpose?
Data Table:
Acid
Volume Acid
Volume NaOH
CH3COOH
HCl
H2SO4
(a) Determine the concentration of each of the acids.
(Molarity = moles / liter: Compare using the inverse ratio.)
(Note: For the concentration of H2SO4 double it. Why?)
(b) Determine the percent acid in each solution.
(Percent = mass of acid / mass of solution X 100)
(Sample calculations will be done in class.)