Normalidade

Concentration units

1-Normality of solution:-

Is defined as the number of grams-equivalent weight of solute per one liter of solution .

Molarities of solution :-

A molar solution contains one gram molecular weights of solute dissolved in sufficient amount of solvent to give 1 liter of solution .

Formality :- is the number of grams formula weight of solute per liter of solution. used for partial dissolved solutes (such as acetic acid , oxalic acid etc…)

Preparation of 1% w/v Na2CO3 solution

Weigh 1 gm of sodium carbonate using a watch glass, transfer it into a beaker, then add 50 ml. of distilled water(mix using a stirrer )transfer the solution into a volumetric flask of 100 ml. add distilled water to the mark.

Mix the solution by inverting the flask 2-3 times to mix the component .

Q / prepare 0.3 % solution from 1% solution in 250 ml volumetric flask.

Preparation of 0.1N Na2CO3 solution

Weigh 1.325 gm of Na2CO3 (using a watch glass ) transfer it into a beaker. Add 100 ml of distilled water (using a stirrer to mix), after dissolving , transfer the solution into a volumetric flask of 250 ml then add water to the mark .

Q / From this solution prepare 0.05 N , and 0.02 N solution in 250 ml distill water ?

To prepare dilute solution from stock solution , this law must be used :-

Dilution law is :- (N x V)1 = (N x V)2

Where (1) refer to the concentrated solution and (2) refer to the diluted solution.

To find the normality of concentrated solutions (for liquid only) this law must be used:-

Or :

Q / prepare 2N solution in 250 ml volumetric flask from 5N of HCl stock solution .

Q / prepare 500 ml , 5N H2SO4 solution from original concentrated solution. .

Preparation of 0.1 M Na2CO3 solution in 250 ml D.W

Weight 2.65 gm of Na2CO3 , transfer it into a beaker. Add 100ml of D.W ( mix using a glass stirrer ).Transfer the solution into a 250 ml volumetric flask of, add water to the mark.

So : 1M Na2CO3 = 2N Na2CO3

part per million (PPm )

The concentration of very diluted solutions ,It’s the number of mg of salt dissolved in one liter solution.

Buffer solution

Any solution that contains both a weak acid and it’s weak base, has the ability to absorb small amounts of either a strong acid or strong base are added they are neutralized by the weak base , while small quantities of a strong base are neutralized by the weak acid, such solution are said to be buffer because they resist significant change in the PH .The PH value is determined by a PH meter.

Using of indicators in a PH estimation:-

Principle:-

A set of buffer solution of known PH is prepared form citric acid and disodium monohydrogen phosphate.

The color of the indicator in an unknown solution is compared with the color of indicator in these buffer solution , assuming that the concentration of the indicator in all solution is the same.

The buffer solution in which the color of the indicator is the same as color of the indicator in the unknown solution has the same PH as this solution.

Procedure :-

Fill one burette with citric acid solution 0.1 molar and a second burette with 0.2 molar disodium monohydrogen phosphate ( called solution A and B respectively) .

Use the following table in preparing a set of buffer solutions:-

No PH ml of solution A ml of solution B

1 4.2 5.86 4.14

2 4.4 5.59 4.41

3 4.6 5.33 4.68

4 4.8 5.07 4.93

5 5 4.85 5.15

6 5.2 4.64 5.36

7 5.4 4.43 5.58

8 5.6 4.2 5.8

9 5.8 3.96 6.03

10 6.0 3.69 6.32

The way to work is follows:-

1- Label

...