Volumetric Analysis

Concentration of solution:

Gram per litre

The weight of solute in gram present in 1 litre of a solution is called gram per litre.
If V cc of a solution contains W gm of solute
1 cc of a solution contains W/V gm of solute
1000 cc of a solution contains (W/V) 1000
So,

Gram\ per\ litre = \frac{W}{V} \times 1000

Normality

The number of gram equivalent of solute present in 1 litre of a solution is called normality.
49 gm of H₂SO₄ in 1000 cc gives 1N solution
98 gm of H₂SO₄ in 1000 cc gives 2N solution.
So,

\begin{align*} Normality &= \frac{Gram\ per\ litre}{eq.\ wt}\\ &= \frac{W}{V} \times \frac{1000}{eq.\ wt} \end{align*}

Molarity

The number of moles of solute present in 1 litre of a solution is called normality.
98 gm of H₂SO₄ in 1000 cc gives 1M solution
49 gm of H₂SO₄ in 1000 cc gives M/2 solution.
So,

\begin{align*} Molarity &= \frac{Gram\ per\ litre}{mol.\ wt}\\ &= \frac{W}{V} \times \frac{1000}{mol.\ wt} \end{align*}

Percentage strength

The weight of solute in gram present in 100 cc of a solution is called percentage strength. 10% solution implies 100 cc solution contains 10 gm of solute
If V cc solution contains W gm of solute
1cc solution contains W/V gm of solute
100cc solution contains (W/V) 100 gm of solute.
So,

Percentage\ strength = \frac{W}{V} \times 100

Molality

The number of moles of solute dissolved in 1 kg of a solvent is called molality.
So,

\begin{align*} Molality &= \frac{Mass\ of\ solute}{Mass\ of\ solvent}\\ &= \frac{W \times 1000}{M \times W_{sol}(gm)} \end{align*}

Parts per million (ppm)

It is defined as the mass of solute present in one million parts (10⁶) by the weight of the solution.

Part\ per\ million = \frac{Mass\ of\ solute}{Mass\ of\ solution} \times 10^{6}

Parts per billion

It is defined as the mass of solute present in one million parts (10⁹) by weight of the solution.

Part\ per\ billion = \frac{Mass\ of\ solute}{Mass\ of\ solution} \times 10^{9}

Relation between normality and molarity

\begin{align*} Normality &= \frac{W}{V} \times \frac{1000}{Eq.\ wt.}\ --(i)\\ Molarity &= \frac{W}{V} \times \frac{1000}{Mol.\ wt.}\ --(ii)\\ & Dividing\ eqn\ (i)\ by\ (ii),\ we\ get,\\ \frac{Normality}{Molarity} &= \frac{Mol.\ wt.}{Eq.\ wt.} \end{align*}

For monobasic acid (HCl) or monoacidic base (NaOH)
Molecular weight = Equivalent weight
So, Molarity = Normality

For dibasic acid (H₂SO₄) or diacidic acid [Ca(OH)₂]:
Molecular weight = 2 x equivalent weight
Molarity = Normality/2

In General:
For an acid of basicity ‘n’ or a base of acidity ‘n’,
Molarity = Normality/n
For salt,
n = total number of charges in acid or basic radical

Standard Solutioon

A solution that contains a known weight of solute in a known volume of it is called a standard solution.
36.5 grams of HCl in 1000 cc gives 1N solution.

Primary standard solution

A solution that contains a known weight of the primary standard substance in a known volume of it is called the primary standard solution.
Following are the essential condition to be a primary standard substance:

• The substance should be easily available in the pure state.
• The substance should not be highly reactive and highly hydroscopic.
• The composition of the substance should not change in solid-state as well as in solution state for a long time.
• The substance should have equivalent weight which causes a minimum error during weighing. Some primary standard substances are oxalic acid crystals, anhydrous sodium carbonate, mohr’s salt, NaCl, KCl, etc.

Secondary standard solution

All solutions of exact concentration cannot be prepared directly because some substance that interacts with air or moisture may be present in impure form. In such conditions, these prepared solutions are required to be standardized and these types of solute substances are called secondary standard solutions. A standard solution that is prepared by using a secondary standard substance is called a secondary standard solution.
Some secondary standard substances are blue vitriol, borax, KMnO₄, FeSO₄, HCl, HNO₃, H₂SO₄, etc.

Q. Preparation of 250 cc N/10 anhydrous Na₂CO₃ solution
solution:

we know that,

\begin{align*} N &= \frac{W}{V} \times \frac{1000}{eq.\ wt}\\ or,\ W &= \frac{250 \times 53 \times N}{1000 \times 10}\ = 1.325\ gm\\ & so,\ 1.325gm\ of\ Na_{2}CO_{3}\ in\ 1000cc\ \\ &gives\ N/10\ solution. \end{align*}

Normality = \frac{\%\ of\ solute \times sp.\ gravity \times 10}{Eq.\ weight}

Normality factor(f)

It is a number which when multiplied the proposed concentration gives the actual concentration of the solution.
Mathematically,

f=\frac{observed\ weight}{theoritical\ weight}

Normal solution

A solution that contains 1 gm equivalent of solute in 1000 cc of it is called a normal solution. 49 gm of H₂SO₄ in 1000 cc gives 1N solution

Decinormal solution

A solution that contains 1/10th gm equivalent of solute in 1000 cc of it is called a decinormal solution.
4.9 gm of H₂SO₄ in 1000 cc gives N/10 solution.

Seminormal solution

A solution that contains 1/2th gm equivalent of solute in 1000 cc of it is called a seminormal solution.
24.5 gm of H₂SO₄ in 1000 cc gives N/2 solution

Centinormal solution

A solution that contains 1/100th gm equivalent of solute in 1000 cc of it is called centinormal solution.
0.49 gm of H₂SO₄ in 1000 cc gives N/100 solution

Molal solution

A solution that contains 1 mole of solute in 1000 g of solvent is called a molal solution.