Hydroquinone for industrial use (4)

4.

Measure according to the method specified in GB/T617-2006

4.

4.

4.

4.

4.

4.

Weigh about 5.

4.

The mass fraction w _{3 of the} burning residue , the value is expressed in %, calculated according to formula (3):

Where:

m ₂ -the value of the mass of the crucible and residue after ignition, in grams (g);

m ₁ -the value of the mass of the crucible, in grams (g);

m—The value of the mass of the sample, in grams (g)

Take the arithmetic average of the two parallel determination results as the report result

4.

4.

Under weakly acidic conditions, the heavy metal (lead) ion in the sample reacts with sodium sulfide to generate lead sulfide

4.
8.
2 Reagents

4.
8.
2.
1 Hydrochloric acid solution: 1+3
.

4.
8.
2.
2 Hydrochloric acid solution: 1+99
.

4.
8.
2.
3 Ammonia solution: 1+9
.

4.
8.
2.
4 Sodium sulfide solution: Rinse a few crystals of sodium sulfide (Na ₂ S·9H ₂ O) with water, absorb the water with a paper towel, and dissolve 5.
0 g of this crystal with 100 mL of water
.

4.
8.
2.
5 Acetic acid-sodium acetate buffer solution: pH 4～5
.

4.
8.
2.
6 p-nitrophenol indicator solution: 2.
5g/L
.

4.
8.
2.
7 Lead (Pb) standard solution: 0.
01mg/mL
.
It is made by diluting 0.
1mg/mL lead (Pb) standard solution with water before use
.

4.
8.
3 Apparatus

Colorimetric tube: 50mL
.

4.
8.
4 Analysis steps

4.
8.
4.
1 Preparation of sample solution

Add 2mL hydrochloric acid solution (4.
8.
2.
1) to dissolve the residue A after ignition retained in 4.
7.
2, transfer quantitatively to a 25mL volumetric flask with water, dilute to the mark, and shake well
.

4.
8.
4.
2 Determination

Measure (5.
0±0.
05) mL sample solution and (2.
0±0.
05) mL lead (Pb) standard solution in two 50 mL beakers
.
Add 2 drops of p-nitrophenol indicator solution to each.
If the solution is colorless, add ammonia solution until the solution turns yellow, then add hydrochloric acid solution (4.
8.
2.
2) until the solution becomes colorless, and an excess of 1 mL is added.
Dilute to the mark with water in a 50ml.
volumetric flask and mix thoroughly
.
Measure (20.
0±0.
05) mL of the above two solutions in two colorimetric tubes
.
Add 10ml sodium sulfide solution to each of the two colorimetric tubes, dilute to 50ml with water, and mix well
.
The color produced by the sample solution should not be darker than the color produced by the lead (Pb) standard solution
.

Related links: Hydroquinone for industrial use (3)