1. Ravi Prapharsavat
IB chemistrySL2
September16,2010
Determine the acetic acid in commercial vinegar
Introduction:
The researchbeingconductedinthe labis to prove thatcommercial vinegarcontains five
percentof aceticacid, bytitrationmethod.Asaceticacidis an organiccompound,itreacts withbases
such as NaOHto form saltand water.
CH3COOH+ NaOH  NaCH3COO+H2O
The balancedchemical equationforneutralizationof aceticacidwithNaOH,andthe
equivalence pointof thisneutralizationreactioncanbe determine usingachemical indicatortosignal
the endpointsuch as Phenolphthalein.
The titrationmethodisthat a drop of a solution(substance,inthiscase NaOHand vinegar) to
anothersolution(substance,inthiscase VinegarandNaOHwithindicator) todeterminedthe
concentration. The dropscontinue until the titrationmeetsthe EndPoint,whichisthe suddenchange
ina physical property,suchasthe indicatorcolor(inthiscaseitturns pink).The standardizationisthen
use,wherebythe concentrationof areagentisdeterminebyreactionwithaknownquantityof a second
reagent.Therefore,accordingtothe theoryof titrationandacetic acidreactingwithNaOH,the
standardizationshouldgive apercentage of how muchaceticacid isinthe commercial vinegar.
Design:
Research Question:Prove thatcommercial vinegarcontained5% of aceticacid.
Control Variables:NaOH(constantamount),Vinegar(constantamount),andphenolphthalein(constant
drops)
DependentVariables:the amountusedbythe NaOH and vinegarsolutioninthe burret
Independent Variable: the constant amount and concentration of the solutions (NaOH, Phenolphthalein,
and vinegar)
Equipment:125 mL Erlenmeyerflasks,50mL beret,beretstandandclamp
Chemical:o.5 M. of NaOH, Phenolphthalein(chemical indicator),andcommercial vinegarclaimingto
contain5% acetic acid
Procedure:
 Pour20mL of vinegarintothe 125 mL Erlenmeyerflask
Equation:1

2.  Fill the burretwith50 mL of NaOH
solution
 Add4 dropsof the chemical
indicatortothe vinegarsolutionin
the Erlenmeyerflask
 Performthe titrationuntil the
vinegarandindicatorsolutionturns
and remainslightpink
 Recordthe final volume of NaOH
solutioninside of the burret
 Performthisexperimentation
anothertwotimes.
 Whenfinishthe trials,repeatitagain
three timesbut istime withvinegar
inthe burret
 Usingthe volume andthe molarities
of NaOH,and the volume anddensityof vinegar,the percentage of aceticacidwill be calculated
Data Collectionand Processing:
NaOH Reading
Trials Initial volume of NaOH
in Burret (mL) ±0.05
Final volume of NaOH
in Burret (mL) ±0.6
Volume of NaOH used
(initial volume-Final
volume) (mL) ± 0.6
1 50.0 13.5 36.5
2 50.0 14.5 35.5
3 50.0 15.8 34.2
Average 14.6 35.4
Vinegar Reading
Trials Initial volume of
Vinegarin Burret (mL)
±0.05
Final volume of Vinegar
in Burret (mL) ±1
Volume of Vinegar
used(initial volume-
Final volume) (mL) ± 1
1 50.0 28.1 31.1
2 50.0 29.0 33.2
3 50.0 30.2 32.1
Average 29.1 32.1
Table 1: indicate the NaOHsolutionasit comesto the endpoint,where the solutionusedinthe
Erlenmeyerflask.
Table 2: indicate the vinegarsolutionasitcomestothe endpoint,where the solutionusedinthe
Erlenmeyerflask.

3. Densityof Vinegar= 1.01 g/mL
Molarity of Vinegar=0.5 M
True value of CH3COOH= 5.00 %
Sample Calculation:
Uncertainties:
𝑈𝑛𝑐𝑒𝑟𝑡𝑎𝑖𝑛𝑡𝑖𝑒𝑠 =
𝑟𝑎𝑛𝑔𝑒
2
Example:
𝑈𝑛𝑐𝑒𝑟𝑡𝑎𝑖𝑛𝑡𝑖𝑒𝑠 𝑖𝑛 𝑡ℎ𝑒 "𝑓𝑖𝑛𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑣𝑖𝑛𝑒𝑔𝑎𝑟 𝑖𝑛 𝑏𝑢𝑟𝑟𝑒𝑡 =
30.2 − 28.1
2
= 1.0 (𝑡𝑜 1 𝑑. 𝑝)
Calculationof the percentage ofacetic acid incommercial vinegar:
𝑀𝑜𝑙𝑒𝑠 𝑜𝑓 𝑁𝑎𝑂𝐻 = 𝑉𝑜𝑙𝑢𝑚𝑒 × 𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦
= 35.4 × 0.5
𝑚𝑜𝑙
1000
= 0.0177 𝑚𝑜𝑙𝑒𝑠
𝑀𝑜𝑙𝑒𝑠 𝑜𝑓 𝑎𝑐𝑒𝑡𝑖𝑐 𝑎𝑐𝑖𝑑 = 0.0177 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑁𝑎𝑂𝐻 × (1 𝑚𝑜𝑙 𝑎𝑐𝑒𝑡𝑖𝑐 𝑎𝑐𝑖𝑑 ÷ 1 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻)
= 0.0177 × (
60.0𝑔
𝑚𝑜𝑙
)
= 1.062 𝑔𝑟𝑎𝑚𝑠
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑉𝑖𝑛𝑒𝑔𝑎𝑟 𝑠𝑎𝑚𝑝𝑙𝑒 = 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 × 𝑉𝑜𝑙𝑢𝑚𝑒
=
1.01𝑔
𝑚𝐿
× 32.1 𝑚𝐿
= 32.421 𝑔𝑟𝑎𝑚𝑠
% 𝑜𝑓 𝑎𝑐𝑒𝑡𝑖𝑐 𝑎𝑐𝑖𝑑 𝑖𝑛 𝑉𝑖𝑛𝑒𝑔𝑎𝑟 = (
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑎𝑐𝑒𝑡𝑖𝑐 𝑎𝑐𝑖𝑑
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑣𝑖𝑛𝑒𝑔𝑎𝑟
) × 100
= (
1.062𝑔
32.412𝑔
) × 100
= 3.3%

4. % 𝐸𝑟𝑟𝑜𝑟 =
𝑡𝑟𝑢𝑒 − 𝑜𝑏𝑠𝑒𝑟𝑣𝑒
𝑡𝑟𝑢𝑒
× 100
=
5.00−3.3
5.00
× 100
= 4.5% (𝑡𝑜 1 𝑑. 𝑝)
Conclusionand Evaluation:
The commercial vinegardoesnotcontained5% of acetic acidas it isstatedin the bottle,
howeveritispossible.The percentage of CH3COOHinthe sample vinegaris foundtobe 3.3%, however,
the label indicate thatits5.00%, whichgivesthe deviationof the experimental value fromthe true value
to be 1.7. By usingthe true value,a percentage errorwascalculatedtobe 4.5%; the experimental
percentage of CH3COOHinthe vinegarsample islowerthanthe true value.
There are two weaknessesthathave beenencounterinthisexperimentation.One possible error
that mightbe takento an account ishow the titration couldpastthe true equivalence pointof the
reaction.Bybeingaccurate in the color change will resultinalessNaOHor vinegarvalue used inthe
burret.Anotherweaknessthatisencounteredinthe experimentationis: the solutionissometimes
mixedwithwater,andthereforecauses the aceticacidas well asNaOHto be lessconcentrated;
resultinginreactingslower(turningpinkslower). The solutions,suchasthe vinegarand NaOH,are left
openon the table.Therefore the molecule evaporate,leacingitwithmostlywater,whichthe aceticacid
and NaOHwill become lessconcentrated.If the NaOHand the vinegarare new andthe lidsare close,
the resultmightindicate asmallervolume of NaOHused,whichincreasethe percentageof the acetic
acid.