Preparing a standard solution

1. What is a Standard Solution?

• A standard solution is a solution with a known concentration that remains constant over time.
• Used in laboratories for accurate chemical analysis.

Concentration Formula:

$c = \frac{n}{V}$

where:

• $c =$ concentration $(mol·dm⁻³)$
• $n =$ number of moles of solute $(mol)$
• $V =$ volume of solution $(dm³)$

2. Difference Between Concentrated and Dilute Solutions

Solution Type	Description
Concentrated Solution	High number of moles of solute per unit volume
Dilute Solution	Low number of moles of solute per unit volume

Dilution Formula:

$c_1V_1 = c_2V_2$

where:

• $c₁, V₁ =$ concentration and volume of the concentrated solution
• $c₂, V₂$= concentration and volume of the dilute solution

3. Steps to Prepare a Standard Solution

Step 1: Calculate the Required Mass of Solute

• Use molar mass to calculate how much solute is needed.
• Example: For $NaOH$ ($$Molar $Mass = 40$ g·mol⁻¹$$), calculate mass for 0.5 mol·dm⁻³ in 200 cm³ solution:

$\text{Mass} = 40 \times 0.1 = 4.0 \text{ g}$

Step 2: Weigh the Solute

• Use an electronic balance to measure exact mass of solute.

Step 3: Transfer to a Volumetric Flask

• Add solute to a volumetric flask.
• Add distilled water (100 cm³) and swirl until solute fully dissolves.

Step 4: Adjust to Final Volume

• Slowly add distilled water up to the calibration mark on the flask.

Step 5: Calculate the Final Concentration

• If a small error occurs in weighing, use: $c = \frac{n}{V}$

• Adjust final value accordingly.

4. Key Definitions

Term	Definition
Solute	The solid substance dissolved in a solution.
Solvent	The liquid in which the solute dissolves (usually water).
Solution	The final mixture of solute and solvent.

5. Summary of Standard Solution Preparation

✅ Use accurate calculations to determine the required solute mass.

✅ Use distilled water to ensure purity.

✅ Swirl the solution to ensure complete dissolution.

✅ Measure final volume precisely in a volumetric flask.