Acid & Base titrations: MCQ 3

Study Notes

Standard Solution

A standard solution is a solution whose concentration is accurately known.
Primary standards are used to make a standard solution, and very few chemicals are suitable as primary standards.
A primary standard is a water-soluble substance that is stable and available in pure form.
Anhydrous sodium carbonate (Na₂CO₃) is a common primary standard.

Preparation of Standard Solution

Weigh an appropriate amount of solute on an analytical balance into a weigh boat.
Use a stirring rod to dissolve the solute.
Wash the stirring rod with deionised water using a wash bottle.
Transfer the solution to a volumetric flask using a funnel.
Rinse the beaker and add washings to the volumetric flask.
Add deionised water dropwise until the bottom of the meniscus rests on the graduation mark.
Stopper the solution and invert the flask 10 times to fully mix the solution.

Effect of Dilution on Concentration

When a coloured solution is diluted, its shade will become paler.
A stronger colour means a more concentrated solution.
The concentration of a diluted solution can be calculated using the formula: M₁V₁ = M₂V₂.

Acid and Base Titrations

These titrations involve adding acid from a burette to a base in a conical flask.
The acid is added until a colour change indicates that neutralisation has occurred.
If the concentration of one solution is known, it can be used to determine the unknown concentration of the other solution.

Procedures to Ensure Accurate Titrations

Burette:
- Wash out with deionised water.
- Add solution to the burette using a funnel.
- Open the tap briefly to fill the part of the burette below the tap (the jet).
- Top up above the 0 cm³ mark.
- Remove the funnel.
- Open the tap and release solution until the bottom of the meniscus rests on the 0 cm³ mark.
Pipette:
- Wash out with deionised water.
- Use a pipette filler to bring the solution into the pipette.
- Fill until the bottom of the meniscus rests on the graduation mark when viewed from eye level.
- Fully release the solution and then place the tip of the pipette against the inside of the conical flask for about 3 seconds.
Conical flask:
- Wash out with deionised water only.
- Add a few drops of indicator.
- Place a white tile under the conical flask.
- During the titration, wash down the sides of the conical flask from time to time to ensure that none of the reactants are adhering to the glass.

Description

Learn how to prepare a standard solution in chemistry, including the use of primary standards and accurate concentration measurements. Understand the importance of standard solutions in chemical analysis.