Acid-Base Titrations Pre-lab Questions (10 Points) Show calculations in space pr
ID: 1000714 • Letter: A
Question
Acid-Base Titrations
Pre-lab Questions (10 Points)
Show calculations in space provided or on a separate sheet of paper.
1. In an experiment, 39.26 mL of 0.1062 M NaOH solution was required to titrate 37.54 mL of unknown acetic acid solution to a phenolphthalein end point. Calculate the molarity of the acetic acid solution, and the percent (by weight) of acetic acid in the solution (assuming its density to be 1.00 g/mL).
________________________________ M ____________________________________%
2. What is the proper disposal of all chemicals in this experiment?
3. List some the hazards associated with sodium hydroxide.
Explanation / Answer
Let for NaOH solution,
M1 = 0.1062 M and V1 = 39.26 mL
And for Acetic acid AcOH solution,
M2 = ?, and V2 = 37.54 mL.
For monoacidic base and monobasic acid, At neutralization point,
Milimoles of H+ = Milimoles of HO–
Milimoles of acid = Milimoles of base
Milimoles of AcOH = Milimoles of NaOH
Milimoles of = Molarity x Volume in mL.
Hence we write,
M2 x V2 for AcOH = M1 x V1 for NaOH
M2 x 37.54 = 0.1062 x 39.26
M2 x 37.54 = 4.1694
M2 = 4.1694/37.54
M2 = 0.1111 M
Molarity of acetic acid solution is 0.1111 M.
Given that this acetic acid has density 1g/mL
It means, 1000 mL of 0.1111 M AcOH solution weigh 1000 g.
Let us calculate mass of AcOH dissolved in water to make 39.26 mL solution from molarity,
Molar mass of AcOH = 60.05 g/mol
Hence,
0.1111 M AcOH 0.1111 x 60.05 = 6.6716 g AcOH
% (w/w) AcOH = (Weight of AcOH/Total mass of AcOH) x 100
% (w/w) AcOH = 6.6716/1000 x 100
% (w/w) AcOH = 0.66716 = 0.66 %
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2) Disposal of Acid AcOH and Base NaOH
Neutralization
Procedures for neutralizing acids and bases are described in the following three sections.
General neutralization procedures:
Perform neutralizations carefully, as vapours and heat may be generated. Wear personal protective equipment including apron, gloves and goggles. A face shield in combination with safety goggles is recommended.
A face shield alone is not sufficient, safety goggles must be worn when using a face shield.
Keep containers cool during process, such as placing a beaker in a bucket with slushy ice.
Work slowly and Stir constantly.
After neutralization is complete, dispose of down drain connected to a
sewage system followed by 20 parts water to one part neutralized solution.
If no sewer system is available—dispose of in a burial pit as described in
section 2.1.
See annex for specific strengths of acids and bases.
Follow the specific neutralization procedures below for the acid or base.
i) Acid AcOH neutralization
a) While stirring, add acids diluted 1:10 by volume with water to large amounts of an ice water solution (1:10) of base such as sodium carbonate, calcium hydroxide/oxide (lime).
b) Lime is the preferred base if available. Lime forms less water soluble salts which are more safely and easily disposed of. we can use NaOH which also we want to be disposed.
When a pH of at least 5.5 to 9.0 is achieved, dispose of the solution down a drain connected to a sewage system (if available) followed by 20 parts water to one part neutralized solution
ii) )Base neutralization
a)Add the base to a large vessel containing water (1:10). Slowly add a dilute solution of hydrochloric acid or AcOH can also be used.
When a pH of at least 5.5 to 9.0 is achieved, dispose of the solution down a drain connected to a sewage system (if available) followed by 20 parts water to one part neutralized solution.
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3) Hazards of NaOH:
1) NaOH is corrosive, irritant, and permeator.
2) It’s dissolution in water is an exothermic reaction and hence it cause sever burns when comes in contact with skin, Tissue damage depends on length of contact and time.
3) Eye contact cause corneal damage or even blindness.
4) Over-exposure can produce lung damage, choking, unconsciousness or death. Inflammation of the eye is characterized by redness, watering, and itching.
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