Chem Formal Lab

Topics: Sodium hydroxide, Acetic acid, Base Pages: 5 (1250 words) Published: January 6, 2009
Ghazali Ahmad

Dec. 1 2008



The Concentration of Acetic Acid in Vinegar Lab

The lab I have done is the Concentration of Acetic Acid Lab. In this lab we find the concentration of the acetic acid in the 10 ml of vinegar I had. This kind of lab is called a titration. A titration can be defined as a procedure used to accurately determine the concentration of an unknown solution. Vinegar is an acid, which means that in a chemical reaction it will donate its hydrogen ion. A base is the chemical (or element) that accepts the hydrogen. Acids also have a low pH. Bases have a higher pH. pH is basically a scale that measures the hydrogen ion concentration. To tell when the reaction between the vinegar and the sodium hydroxide, known as a neutralization reaction, has occurred and the solution is now neutral we use indicators. A neutralization reaction is a reaction between an acid and a base. When the acid and base chemically react with each other they always create salt and water. In this case the salt formed is sodium acetate. An indicator is a weak acid or base that changes colour when you have added the precise number of moles that is needed to react completely react the reagent in the flask and the solution in the burette. At the point of the colour change it is assumed that you have reached the “stoichiometric point”. The stoichiometric point is a theoretical point where you have added just enough of the solution to react with the solution in the flask.

Purpose: To determine if Allen’s vinegar or No Name vinegar has a greater concentration of acetic acid. Hypothesis: If we test both of the types of vinegar than we will find that the Allen’s vinegar has the greater concentration because the No name brand is cheaper and to minimize their cost they will use less acetic acid in their solutions and more water. Materials:

suction bulb
retort stand
burette clamp
3 beakers (250ml)
meniscus reader
sheet of white paper
table vinegar (Allen's)
pickling vinegar
sodium hydroxide solution (0.5M)
dropper bottle containing phenolphthalein

Refer to handout


Burette Readings for the Titration of Acetic Acid

Trial 1
Trail 2
Trail 3

25.8 ml
45.55 ml
36.15 ml

5.50 ml
25.80 ml
17.53 ml

Volume added
20.30 ml
19.75 ml
18.62 ml

The trend in this table is that it takes about 20 ml of sodium hydroxide to neutralize the acetic acid. Analysis/ Discussion:
The average of my two closest burette readings is 20.03 ml. I got this number by adding the “volume added” from trials one and two (because they have a difference of 0.55 unlike the third which has a minimum difference of 1.33), which were 20.30 and 19.75 and then dividing by 2. The total volume added was 40.05 ml and dividing it buy two I got 20.03 ml. mathematically this is what it looks like: 20.30 + 19.75 / 2 = avg

40.05 / 2 = avg
20.03 = avg
The chemical equation for the reaction of acetic acid and sodium hydroxide is HC2H3O2 + NaOH ------> NaC2H3O2 + H2O The concentration of acetic acid in the vinegar sample is 0.978 mol/L. I got this by first finding out the moles of sodium hydroxide. I used the concentration of the sodium hydroxide and the volume and multiplied them. It was a 0.5 mol/L solution and I used 20.03 ml (on average) which is 0.02003 L. The product is 0.01. Now I used that and multiplied it by one mol of acetic acid for every mole of sodium hydroxide. I further went on to divide the moles of acetic acid and I divided it by the volume of the vinegar I used, 10 ml (0.01 L). The answer I got from that was the number of moles in every 10 ml of vinegar which was 1 mol/L of acetic acid.

The molar mass of acetic acid is just addition of all of the elements in it. Its molecular formula is HC2H3O2 . There are four hydrogen atoms, two carbon atoms and three oxygen atoms....
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