Chem 2A,B,C Experiments

Bài II
Phương pháp phân tích thể tích
(Volumetric analysis) (Chem 2A – p.25)


The Order and Main Guide Lines

EXP1. Standardizing the unknown base NaOH using the primary standard solution 0.1M KHP potassium acid phthalate (Do 3 times)
Using pipet to take 10 mL 0.1M KHP into into each of three clean 250 mL Erlenmeyer flasks.
Add three drops of phenolphthalein indicator to the first KHP solution
Drop slowly unknown NaOH solution from the buret into flask while stirring well until the color change form colorless to faint pink.
Note the volume of NaOH used from the buret.
Calculate the average volume of NaOH and then calculate the concentration of NaOH solution.
NOTE: KHP has the actual chemical formula KHC8H4O4, (MM = 204.23).


EXP2. Analysis of the Unknown Acetic Acid Solution CH3COOH (using secondary standard solution of sodium hydroxide NaOH known in Exp1.) (Do 3 times)
Using pipet to take 10 mL unkown CH3COOH solution into each of three clean 250 mL Erlenmeyer flasks.
Add three drops of phenolphthalein indicator to that CH3COOH solution.
Drop slowly NaOH solution from the buret into flask while stirring well until the color change from courless to faint pink.
Note the volume of NaOH used from the buret.
Calculate the average volume of NaOH and then calculate the concentration of CH3COOH solution.



EXP3. Standardizing the acid HCl using sodium hydroxide NaOH (known in Exp1.) (do 2 times).
Using pipet to take 5 mL unkown HCl solution into each of two clean 250 mL Erlenmeyer flasks add approximately 20 mL of deionized water to the flask to allow you to swirl the contents easily.
Add 2-3 drops of phenolphthalein indicator to the flask.
Rinse and fill a 30 mL buret with your standard NaOH solution (Exp1.) then drop slowly NaOH solution from the buret into flask while stirring well until the color change from courless to faint pink.
Record the final volume of base and their average volume. Calculate the actual concentration of your hydrochloric acid solution HCl.

EXP4.Antacid Analysis
Take one piece of antacid tablet from the bottle provided in the laboratory. Record the masses of the tablets in your notebook. Crush the antacid tablet using a mortar and pestle.
Quantitatively transfer the sample powder of antacid into the clean 250 mL Erlenmeyer flask then using pipet to take 10 mL (0.6N HCl and add more 25 mL H2O.
Next clamp the flask and heat the contents with a hot plate. Boil the solution for 5 minutes. The sample may not completely dissolve during this process due to the presence of "fillers", but any base will have reacted with the excess HCl. Using your pH indicator paper, check to be sure that all base has reacted, and that there is excess acid present. If the solution is not acidic, then accurately add another 25 mL of acid and boil for another 5 minutes.
Cool the solution to room temperature by carefully immersing the flask in a container of tap water. Add 5 drops of methyl orange indicator (MOXC) to the solution. Titrate the sample with your NaOH standard (known concentration in EXP1). The indicator MOXC goes from red (acid), through grey, to green (base). The grey color is the end-point. The end point is not as obvious as that of phenolphthalein.
Report the neutralization capacity (millimoles of HCl neutralized) of the antacid tablet you used. Calculate the mass and percentage of hydroxide or "equivalent hydroxide" per gram of antacid tablet.
Chem 2A,B,C Experiments
Bài III
Bài 3: Phương pháp trắc quang (Spectrophotometry)
(Chem 2A – p.35)


The Order and Main Guide Lines

In this experiment you will be performing a spectroscopic analysis of known and unknown compounds and mixtures. You will be using the GENESYSTM 20 to find the concentration of an unknown mixture of Bromothymol Blue (BTB) and Thymol Blue (TB).
Part I. Solution Preparation
Already have these solutions:
23.2 μM stock solution BTB in a pH 8.0 buffer
61.6 μM stock solution TB in a pH 8.0 buffer.
pH 8.0 buffer
Preparation of the 23.2 μM Bromothymol Blue Solution
Using 10 mL pipet and five 50 mL beakers
Beaker
1
2
3
4
5

BTB (mL)
25
20
15
10
5

Buffer (mL)
0
5
10
15
20

BTB Concentration







2. Preparation of the 61.6 μM Thymol Blue Solution
Using 10 mL pipet and five 50 mL beakers
Beaker
1
2
3
4
5

TB (mL)
25
20
15
10
5

Buffer (mL)
0
5
10
15
20

TB Concentration






3