what is purity?


what is purity?

What is purity? A measure of the net content of a substance.
The materials used in the lab or industry have some impurity.
They usually have different impurities.
Use purity or purity to indicate the net content of the material
Which follows the following relationship:
Mass of gross mass / Mass of pure matter = Degree of purity
Mass of gross mass / 100 * Mass of pure matter = Percent purity
For example, when we talk about sodium chloride 90% it means
If we divide this piece of salt into 100 parts, it is 90 parts pure sodium chloride and 10 parts are impurities.


Chemical formula: Na-OH

Molecular Weight: 40 CAS: 1310-73-2

RTECS: WB490000

Synonyms: Sodium hydroxide, caustic soda

Features: It is an odorless, white crystalline, transparent, non-volatile and highly corrosive.

Moisture absorbs air easily.


OSHA: 2 mg / m3

NIOSH: 2 mg / m3 / 15 min C; Group I Pesticide

ACGIH: 2 mg / m3 C

Materials and solutions required:

Sodium carbonate, with the original standard purity

Solution Acetate hydrochloric acid, 0.1 normal;

The basic standard is Sodium carbonate.

Hydrochloric acid, 0.01 normal; 10 ml of the acetic acid solution of hydrochloric acid 0.1 normal

Place in a 100 ml bottle of distilled water.

Distilled water is deionized, free of CO2, boiled then cooled with nitrogen.

Compressed Nitrogen

sodium hydroxide 50% (w / v);
50 g of caustic soda dissolved in distilled water

And the volume of 100 ml.

make a caustic soda stokes, 0.1 normal;
add 8 ml of 50% caustic soda to 1 liter CO2-free distilled water.

the practical standard solution of caustic soda, 0.01 normal;
10 ml solution of caustic soda stoke

Exert a 0.1% normal boil with 100 ml CO2-free distilled water

The standard buffer solution with pH 4 and 710-

Required equipment:

Sampler: 37 mm PTFE membrane filter with 1-micron pore size
(Millipore, Fluorophore or similar types).

With a celluloid support pad, with cassette in the filter holder.

Individual sampling pump with a discharge rate of 4-1 L / min,
with flexible interface pipes

pH meter with pH electrode and recorder

Titration container; balloons of 150 to 200 ml;

With a cover that has a hole for the PH electrode as well as the input and output N2

Magnetic stirrer

Glass rod, 5 mm in diameter and 10 cm in length,

To keep the filter below the liquid level in the titration vessel

Pipettes 5 and 10 ml

Balloons of 100 ml and 1 liter

A 50 ml burette with a grade of 0.1 ml



Calibrate individual sampler pumps.

Also, attach a sampler to the pump during calibration.

Perform sampling in a flow rate between 4-1 L / min for air volume flow of 70 to 1000 liters.

Do not allow more than 2 mg of total dust to be collected on the filter.


Transfer the sample filter to the titration container by tweezers.

Note that the surface on the filter is downward.

Due to the fact that during the analysis of the filter below the liquid level,

Place the glass rod end on the filter center to hold it.

Cover the titration container.

Add 5ml hydrochloric acid 0.01 in a titration vessel.

The titration vessel was placed in a magnetic stirrer and purified by N2 (0.1 L / min)


Let the titration container stay in the mixer for 15 minutes.

Calibration and quality control

Calibrate the pH gauge using buffer solutions (with pH equal to 4 and 7).

Adjust the amounts of 0.1% hydrochloric acid solution to sodium carbonate.

3 to 5 grams of standard sodium carbonate for 4 hours at 250 ˚C.

Then cool it in the desiccator.

Dissolve 2.5 g of sodium carbonate in 1 liter of CO2-free distilled water

And to obtain a sodium carbonate of 0.05 normal.

Transfer 5 ml of sodium carbonate solution 0.05 to the titration container

Start titration and continue until you reach PH 5.

Remove the PH electrodes and rinse it into the titration container.

To remove the dissolved CO2, add N2 to the contents of the titration container for 3 to 5 minutes.

Continue titration to the turning point.

Calculate the acidity of the hydrochloric acid solution by the following equation:

N_HCl = ((weighing g Na_2 CO_3) (titration in the case of use NaCl CO 2) / ((52.99)) used HCl ()

The practical Standard solution of caustic soda with the normal solution with the homogeneous hydrochloric acid solution.

Perform this according to step 2 of calibration, except that the hydrochloric acid solution is homogeneous

Alternate with sodium carbonate solution (Na2CO3) and a 0.1% normalized caustic soda solution with the normal hydrochloric acid solution.

Calculate the normality of the caustic soda titration using the following equation.

N1aOH = ((N-HCl) (mL HCl used)) / (mL NaOH used)

Prepare at least three spike checks in order to check the amount of recycling in the range for which the sample is intended.


The excess hydrochloric acid in the main sample, control and spike samples

Reverse titration with standardized (coherent) caustic soda.

Simultaneously clean up with nitrogen.

Look at the PH meter as you type.

Determine the end point (ml of caustic soda used normal 0.01)


Carbon dioxide in the air may

Reacts on the filter with alkali and forms carbonates

But it does not interfere with the titration.

Carbonates can cause positive interference.

Acid particles can neutralize the sample and have negative interactions


Calculate the concentration of caustic soda in the air using the following equation:

C = ((V_ (NaOH-b) -V_ (NaOH-S)) .N × 40 × 〖10〗 ^ 3) / V

In this regard:

C = concentration of caustic soda in mg / m3

The NaOH-b = volume of caustic soda in the titration of the control sample in milliliters

The NaOH-s = volume of caustic soda in the titration of the original sample in milliliters

N = Sodium nitride solution normalization

40 = Molecular weight of caustic soda

V = Sample volume of air in liters

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