Industrial formaldehyde solution (2)

4 Test method

The reagents and water used in this standard, unless other requirements are specified, all use Grade 3 water that meets GB/T6682

The standard solutions, preparations and products used in this standard shall be prepared in accordance with GB/T601 and GB/T603 unless other requirements are indicated

4.

4.

Density meter: value of indexing 0.

4.

According to 2.

Take the arithmetic average of the two parallel determination results as the determination result, and the difference between the two parallel determination results shall not exceed 0.

4.

4.

Formaldehyde reacts with excess neutral sodium sulfite solution to generate sodium hydroxide , using thymolphthalein as an indicator, and titrating with a sulfuric acid standard titration solution

HCHO+Na ₂ SO ₃ +H ₂ O=H ₂ C(OH)SO ₃ Na+NaOH

4.

4.

4.

4.

4.
2.
3 Analysis steps

Add 50 mL of sodium sulfite solution and 3 drops of thymolphthalein indicator solution to a 250 mL conical flask , and neutralize with a sulfuric acid standard titration solution until the blue color just disappears
.
Weigh 1.
3～1.
5g of sample by weight reduction method, accurate to 0.
0002g, put it into the above-mentioned conical flask, titrate with sulfuric acid standard titration solution until the blue color just disappears as the end point
.

4.
2.
4 Expression of analysis results

The formaldehyde content X ₁ expressed by mass white fraction is calculated according to formula (1):

In the formula: V ₁ -the volume of the standard titration solution of sulfuric acid consumed in titration, mL;

c ₁ —The actual concentration of sulfuric acid standard titration solution, mol/L;

m ₁ —the mass of the sample, g;

0.
03003— The mass of formaldehyde in grams equivalent to 1.
00mL sulfuric acid standard titration solution [c(1/2H ₂ SO ₄ )=1.
000mol/L] .

Take the arithmetic mean of the two parallel determination results as the determination result
.
The difference between the two parallel determination results shall not exceed 0.
1%
.