University Of Karachi

CHEMICAL PROCESS TECHNOLOGY

(Practical file)

Syed Saad AhmedB-0933040B.E 3rd Year

Chemical Engineering

Submitted To:Ma’am Khehkashan

CHEMICAL PROCESS TECHNOLOGY 2012

Experiment no. 1

OBJECT:

Preparation of Lead Chromate (PbCrO4) or Chrome Yellow

REAGENTS:

Lead acetate. Potassium chromate. Dilute acetic acid.

THEORY:

Lead chromate is insoluble in water and it is obtained by double decomposition method. It is also known as chrome yellow and used as a pigment. The lead is precipitated as chrome with potassium chromate solution, in a medium buffered with a mixture of acetic acid and lead acetate.

REACTIONS:

(CH 3COO )2Pb+K2CrO4⟶ PbCrO4+2CH 3COOK

PROCEDURE:

Take 5 gm of Lead Acetate and dissolve it in distilled water. Add about 1 ml of dilute Acetic Acid to avoid hydrolysis. Add to it a solution of 3 gm of Potassium chromate. A precipitate of Lead chromate will be formed, heat it to boiling. Wash the precipitate by decantation. Filter it and dry the residue in an oven.

CALCULATION:

Molecular weight of Lead acetate Pb (CH3COO)2 = 325.29 gram/moleMolecular weight of Potassium chromate K2CrO4 = 194.19 gram/moleMolecular weight of Lead chromate PbCrO4 = 323.20 gram/mole

Theoretical yield of PbCrO4:

1 mole Pb (CH3COO)2 produces = 1 mole of PbCrO4

325.29 grams Pb (CH3COO) produces = 323.20 gramsPbCrO4

1 gram Pb (CH3COO) produces =323.20/325.29 gramsPbCrO4

2 Prepared By: Syed Saad Ahmed |

CHEMICAL PROCESS TECHNOLOGY 2012

5 grams Pb (CH3COO) produces = (0.9935) × 5 gramsPbCrO4

5 grams Pb (CH3COO) produces = 4.97 gramsPbCrO4

Practical obtained yield:Practical yield is found to be = 4.33 grams

% yield= practical yieldtheoritical yield

×100

¿ 4.634.97

×100

¿86.9%

RESULTS:

Yield of Lead Chromate (PbCrO4) from this process is 86.9%.

DISCUSSION:

Lead chromate, or chrome yellow, as it is referred to in pigment chemistry is a yellowish crystalline substance or powder that is used as a pigment or coloring agent for ceramics, paints and certain printing.Disadvantage:Lead chromate is a highly toxic chemical and corrosive to lung tissues and implicated in lung cancers. In addition to lung cancers, severe asthmatic reactions can occur along with anemia and neurotoxic effects are also noted. The exposure danger is particularly high for pregnant women and young children. Ingestion of lead chromate causes abdominal pain, nausea and vomiting. After skin contact, dermatitis and ulcers of the skin are possible.Precautions: Nowadays use of lead chromate is banned in many applications like in paints, coloring agents, toys, rubber, printing fabrics etc. Use of lead compounds in domestic surface coatings has been eliminated in Australia. It is being used in industries for lining purpose where it is necessary. Acceptable and superior alternatives are being used instead of the toxic materials.

3 Prepared By: Syed Saad Ahmed |