Last updated: June 22, 2019
Topic: Food
Sample donated:

Most nutrient or family merchandises contain chemicals, and some of them are able to destruct things and injury peoples wellness. The purpose for this experiment is calculate the concentration of the acid and base utilizing titration. The terminal point of a reaction should be observed after chemical solutions were assorted in a conelike flask.

An acid is a substance which can fade out in H2O solution, and alterations it is colour from colourless to red after litmus was added into it. Furthermore, acid can respond with metal and output H gas, and respond with bases to give salts ( Answers, 2010 ) . An Acid can donating proton in chemical reaction, such as, HCl. A base can move as proton receiving systems that turns litmus blue, and output salts after it react with acids. In add-on, it can give hydroxyl ions ( OH- ) when it dissolves in H2O ( Answers, 2010 ) .

Phenolphthalein index ( molecular equation: C20H14O4, figure 1 ) is a weak acid which is a common index for titration. The pH graduated table which phenolphthalein can alter coloring material is from 8.2-10.0, therefore, phenolphthalein can merely indicates alkalic as ruddy or tap coloring material ( Baike. Baidu, 2010 ) . Harmonizing to Lister et Al ( 2000 ) , the phenolphthalein is acidic and demands to bring forth H+ to alter coloring material.

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Figure 1 The Structure of Phenolphthalein ( T4j, 2010 )

Starch, is a natural food saccharide, which molecular equation is ( C6H10O5 ) N, composed of a great trade of glucose monosaccharide units, and occurs in most seeds ( Answer, 2010 ) . In this experiment, amylum was an index for ascertained I, and produced blue-black coloring material.

Syntel Laboratory Ltd ( 2008 ) suggests that, Sodium thiosulphate ( Na2S2O3 ) is used for neutralisation of iodine solution, which the chemical reaction is

2Na2S2O3 ( aq ) + I2 ( s ) & A ; acirc ; † ‘ Na2S4O6 ( aq ) + 2NaI ( s )

Bleach, is a common houseware with the chief constituent being calcium hypochlorite ( Ca ( ClO ) 2 ) and calcium chloride ( CaCl2 ) . Bleach is a sort of base.

Vinegar ( figure 2 ) is a common flavorer in day-to-day life. Lane ( 2010 ) stated that, contains ethanoic acid ( besides called acetic acid ) . The molecular expression of acetum is C2H4O2.

Figure 2 The Structure of Vinegar ( Chemistry, 2010 )

Harmonizing to Answers ( 2010 ) , Sodium hydrated oxide, which chemical equation is NaOH, is a white crystalline substance absorbs C dioxide ( CO2 ) and H2O easy from the air. The chemical equation of reacts with C dioxide is:

2NaOH ( aq ) + CO2 ( cubic decimeter ) & A ; acirc ; † ‘ Na2CO3 ( aq ) + H2O ( cubic decimeter )

The chemical equation of reacts with H2O is:

NaOH ( aq ) & A ; acirc ; † ‘ Na+ ( aq ) + OH- ( aq )

Sodium hydrated oxide is a strong base and able to destruct or fade out other substance easy.



Vinegar, bleach, NaOH ( 0.1M ) , Phenolphthalein Indicator, Na thiosulphate solution ( 0.1M ) , Potassium Iodine ( 1M ) , Sulphuric Acid ( dilute ) and Starch Indicator.


Test tubing ten 6, Funnel x 7, Beaker x 7, Burette x 4, conelike flask x 4, pipette and pipette filler.

Part A

A small NaOH ( 0.1M ) and a small acetum was put into 2 trial tubings used a dropping pipette. 1 bead of phenolphthalein index solution was dropped into each trial tubing, the solutions were observed.

A funnel was put in the top of a burette and NaOH ( 0.1M ) was poured. The NaOH bottle was placed under the burette and the NaOH was poured back into the bottle until the burette degree was 0.0cm3. The exact initial burette reading was written down.

25 cm3 of acetum was poured into the little beaker. 2.5cm3 acetum was put into the conelike flask utilizing a 5cm graduated pipette, the value was written down. 20cm3 of H2O was poured into the conelike flask. 4 beads of phenolphthalein index solution was added.

The conelike flask was put under the burette and some white paper put under the flask to better visibleness. The NaOH ( 0.1M ) solution was added from the burette into the flask, which was shaken continuously to blend the solutions. 1 minute later, some coloring material was changed and was observation disappeared rapidly as the terminal point was neared. NaOH ( 0.1M ) was added easy. 1 bead was added at a clip when the terminal point was appeared. The concluding burette reading was written down. The stairss were repeated three times


The burette was washed and filled with Na thiosulphate solution used a funnel. The reading was recorded. The exact reading was written down. 2cm3 pipette of bleach solution was filled by pipette, and 1cm3 of bleach was transferred. The exact value transferred was written down. 10cm3 of the 1M K iodine solution and 10cm3 of dilute sulfuric acid was added to the conelike flask, I was produced. Sodium thiosulphate solution from the burette was added to the flask, and was swirled continuously. A few beads of amylum index solution were added merely before the terminal point, the coloring material of the solution was monitored. The thiosulphate solution was added dropwise, with thorough swirling. Finally, the terminal point of the titration was detected when the blue-black coloring material changed to colourless. The concluding burette reading was written down. The stairss were repeated one time.


Titrate of Vinegar

At the beginning of this experiment, after NaOH ( 0.1M ) was added into the flask, a violet coloring material appeared, enduring about 2 seconds, and so disappeared. After 10 cm 3 of NaOH ( 0.1M ) added into flask, the coloring material last thirster, approximately 6 seconds, and so disappeared. Finally, when the burette reading became 15.8 centimeter 3, the solution inside flask became violet.


Volume/cm 3

Trial 1

Trial 2

Trial 3

Initial burette reading




Final burette reading




Volume of NaOH ( aq ) for neutralization




Table 2 The information in Titration of Vinegar

Titration of bleach

At the beginning of this experiment, after sulfuric acid was added into the flask, no alteration was observed. Then, KI ( 0.1M ) was added into the flask, the solution turned to brown-yellow coloring material. Starch index was added into flask, the solution turned to blue-black coloring material from brown-yellow coloring material. Finally, as the thiosulphate solution was assorted with the solution, the solution faded to blanch yellow. After the terminal point was occurred, the solution was faded to colourless.


Volume/ cm 3

Trial 1

Trial 2

Initial burette reading



Final burette reading



Volume of NaS2O3



Table 4 Titration of Bleach



The computation of the concentration of ethanoic acid:

mole of NaOH = mole of CH3COOH

degree Celsius ( NaOH ) x V ( 18.55 – 6 ) cm3

0.1mole/l ten 12.55 ten 10-3dm3

degree Celsius ( CH3COOH ) = n ( CH3COOH ) / V ( CH3COOH )

= 1.255 ten 10-3 / 0.25 x 10-3

= 5.02 mol dm-3

( degree Celsius means concentration, 5 agencies volume )

Harmonizing to the information from consequence, the volume of NaOH ( 0.1M ) for neutralization in test 1 is 15.8 cm3, the information is test 2 is 12.55 cm3, in test 3 is 5.93 ; the informations in these tests was diminutions bit by bit. The ground may be because there are some chemical solutions remained in the flask, and influenced the informations.


The Na hypochlorite:

mole of S2O3-

3.4 cm3 x 0.1 mol/l x 10-3

= 3.4 ten 10-4 mol

& A ; acirc ; ?? mole of I2 = ClO-

3.4 ten 10-4/2 = 1.7 ten 10-4 mol

degree Celsiuss = n /v

=1.7 x 10-4/1 x 10-3

=0.17 mol dm3

Harmonizing to the procedure of test 2, the concentration of test 1 was calculated 0.16 mol dm3, and the concentration in test was calculated by the old computation, which every bit to 0.17 mol dm3. However, the normal concentration should be 0.5-0.8 mol dm3.

In add-on, because of the incorrect units transfer in these two experiments and the ill-defined conelike flasks, these two factors caused the consequence was different from the standard value, particularly in experiment B, the mistake had a big difference of the normal value. In following experiment, all units jobs should be avoid and preview it before the experiment ; nevertheless, the equipments which used in experiment should be clean carefully and by the running pat, which can avoid chemicals remain in the equipments.


In decision, these experiments show clearly that the provinces and the coloring material alterations during these two experiment after index was added into the conelike flask. Furthermore, the concentration of these two experiments were calculated by hundred = n/v.