Hydrochloric acid, HCl, is not a primary standard - Leaving Cert Chemistry - Question 2 - 2010

A standard solution is a solution of known exact concentration, which serves as a reference in titrations. It is prepared using a substance that is stable, pure, and soluble in water.

A primary standard is a highly pure compound that can be used to determine the exact concentration of a solution. It must be stable, non-hygroscopic, and readily available. The primary standard is used to prepare a standard solution.

The sodium carbonate used is anhydrous, meaning it does not contain water of crystallisation.

An example of a suitable primary standard is anhydrous sodium carbonate, which is stable, can be obtained in pure form, and is soluble in water.

To ensure all of the sodium carbonate solution is transferred, the glassware should be rinsed with the sodium carbonate solution into the volumetric flask.

After transferring the solution, distilled water is added to the volumetric flask until it reaches the calibration mark on the neck to ensure the final volume is exactly 1 liter.

When performing a titration, it is important to wash the sides of the flask with distilled water to ensure all reactants are in the solution and to prevent any loss of reagents.

This demonstrates the calculation needed using the molar mass of sodium carbonate to find its concentration.

The molar mass of Na₂CO₃ is calculated as follows:

Na: 23 g/mol × 2 = 46 g/mol
C: 12 g/mol = 12 g/mol
O: 16 g/mol × 3 = 48 g/mol

Total: 46 + 12 + 48 = 106 g/mol

Now, using the equation:

ext{Molarity} = rac{ ext{moles of solute}}{ ext{liters of solution}}

We convert 5.3 g of Na₂CO₃ to moles:

To find the molarity (C) of the hydrochloric acid solution, we can use the titration data:

Using the formula from the titration reaction:

rac{27.5 ext{ cm}^3 imes M_1}{2} = rac{25.0 ext{ cm}^3 imes 0.05 ext{ M}}{1}

Solving for $M_1$:

M_1 = rac{25.0 imes 0.05 imes 2}{27.5}

Calculating the value gives:

$M_1 = 0.09 ext{ M}$

Therefore, the molarity of the hydrochloric acid solution is 0.09 M.