- Information
- AI Chat
PAC PRAC 4
Physical Chemistry
University of Fort Hare
Related Studylists
Chem230Preview text
TITLE: The solubility of Benzoic acid in water.
AIM: To determine whether the benzoic acid is soluble in water.
THEORY OF THE EXPERIMENT Benzoic acid C 7 H 6 O 2 (or C 6 H 5 COOH), is a colourless crystalline solid and a simple aromatic it occurs naturally in many plants and it serves as an intermediate in the biosynthesis of many secondary metabolites
ln(K)=−∆H
o R (
1
T)+
∆So R
∆So = entropy, ∆Ho = enthalpy change The above equation also represent the straight line equation where the values can be
obtained from the straight line graph. y = mx + c where ln k is the y-intercept, ∆H
o R
=m gradient and T 1 = x-intercept
PROCEDURE Two spatulas that are about 5g of benzoic acid were transferred into 200ml distilled water in separate reaction flasks. The flasks were suspended in a water bath and shaken periodically to ensure maximum solubility of the benzoic acid. The solutions were allowed to reach thermal equilibrium with the bath temperature. Without removing the flasks from the water bath, 10ml samples were withdrawn from each flask, using a pipette fitted with a filter that prevents solid benzoic acid from being sucked up the pipette. The filter was removed before adjusting the level of solution in the pipette. The outside of the pipette was rinsed with a wash bottle. The 10ml samples were deposited into separate conical flasks and the insides were rinsed into the same flask. Fresh cotton wool was used with every sample that was withdrawn. The amount of benzoic acid was titrated with NaOH in each sample. Two more 10ml samples were withdrawn as before and were titrated as before. The temperature of the water bath was raised by 5°C intervals to 30°C , 35°C , 40°C , 45 °C , 50°C .The samples were withdrawn and titrated as outlined above. It was made sure that sufficient time was allowed for the solutions to reach thermal equilibrium at each bath temperature .In the event of the solution being
depleted ,more water and more benzoic acid were added,enough to make a saturated solution.
ANALYSIS OF DATA
1.
C(NaOH) = nv
n(NaOH) = C(NaOH) x V = (0/L)(0)
=0
Solubility at At 35OC S 1 = 0.04098mol/0 3 = 3 mol/dm
Solubility at 40OC S 2 = 0.04098mol/0 3 = 2 mol/dm 3
Solubility at 45OC S 3 = 0.04098mol/0 3 = 2/dm 3 Solubility at 50OC S 4 = 0.04098mol/0 3 = 1 mol/dm 3
- TEMPERATURE (°C ) S(mol/dm 3 ) ln S 1/T 35 3 mol/dm 3 1 0.
40 2 mol/dm 3 0 0. 45 2/dm 3 0 0. 50 1 mol/dm 3 0 0.
7.
Benzoic acid dissolves only slightly in cold water is that, even though the carboxylic acid group is polar, the bulk of the benzoic acid molecule is non-polar (water is polar). It is only the carboxylic group that is polar. In addition, there are no internal stabilizing structures that favour carboxylate, -COO(-), over carboxylic acid, -COOH. When not in the presence of water, two molecules of benzoic acid may form what is called a dimer. In this instance, one molecule hydrogen-bonds to the second molecule. Beyond hydrogen bond formation, full ionization can take place if there is some causative agent to force this. Bases can force ionization, but to a limited degree water produces ionization, according to the following reaction equation: CH5COOH + H2O → C6H5COO(-) + H3O(+) Ionization guarantees water-solubility, since water is a polar solvent. In addition to temperature changes, there are other ways to increase or decrease the water-solubility of benzoic acid. The addition of a strong acid decreases the ionization through the “common ion” effect. Increasing the pH increases ionization of the benzoic acid, perhaps leading to reaction.
- pH = -log(H+) H+ = 10-pH =10-2. = 1-
[C 6 H 5 COO-] = [H+] = 1-3 M Ka = ¿/ [C 5 H 5 COOH] Ka = (1 10
− 3 −x) 2 x (1 10 − 3 ) (1 10 − 3 +x) 3−x = 6
-
(6-5)(3-X) = 3-6 + 1-3X 1-4 – 6-5X = 3-6 + 1-3X 1-4 - 3-6 = 6-5X + 1-3X 1-4 = 1-3X X = 0. [C 6 H 5 COOH] =3 – X
= 3- 0.
= 2
9.
(a) The crystals of benzoic acid in solution was non spontaneous because benzoic acid dissociate very slowly. At different temperature the (from 25 to 50) the benzoic acid seemed not to dissolve completely in the solution. The concentration of benzoic acid in each solution was determined by titration with 0 NaOH. (b) Adding heat greatly increases solubility because some of the increased energy sufficiently lengthems the hydrogen bonds, so that ionization occurs. Ions are by definition of polar, so the general truism, like dissolve like, indicates the ions will then dissolve in water (c ) Our results gave us a straight line showing that In S is inversely proportional to 1/T however our results do not match with the theoretical values. We may have misread marking on the burette by looking at the measurement on the angle. If looking above, it seems like the volume is lower. If looking from below, the apparent volume is higher. Sometimes it is difficult to read volume at the level of meniscus we may have read a volume at the wrong sport for example taking reading at high section of the curve is an error. (d.) The experimental methods were good. All the apparatus was available and functioning perfectly. Every mixture was prepared well. There were no incoveniences whatsoever.
CONCLUSION
The conclusion from this experiment is that the experimental technique described for measuring the solubility of a solute in a liquid, at different temperatures, is perfectly suitable and easy to achieve. The results show that it is possible to obtain good results for solubility values, using simple procedures. The experimental values obtained for
SURNAME :CWAYI
INITIALS :H
STUDENT# :
COURSE CODE :PAC 224
PRACTICAL# :
TITLE : Solubility of
benzoic acid in water.
DUE DATE :20/09/
PAC PRAC 4
Course: Physical Chemistry
University: University of Fort Hare
This is a preview
Access to all documents
Get Unlimited Downloads
Improve your grades
