Atomic weight determination of covalent metal M

Experiment to determine the atomic weight of covalent metal M using acid-base titration of its hydroxide with 0.1M HCl and phenolphthalein indicator.

Principle

MOH is a base. Therefore, neutralize it by titrating with standard HCl:

$MOH+HCl→MCl+H2O\text{MOH} + \text{HCl} \rightarrow \text{MCl} + \text{H}_2\text{O}$

The mole ratio is 1:1. Use 0.1 M HCl as the standard solution and phenolphthalein as the indicator. The endpoint occurs at the just disappearance of pink.

Reagents & Apparatus

MOH solution (4 g MOH dissolved per dm³)
0.1 M HCl (standard)
Burette, pipette (10 cm³), conical flask, funnel
Phenolphthalein indicator, white tile, wash bottle, clamp stand, etc.

Procedure

First, rinse the burette with small portions of 0.1 M HCl, then fill it and note the initial reading.
Next, pipette 10.0 cm³ of the given MOH solution into a clean conical flask.
Then, add 2–3 drops of phenolphthalein to the flask and place it on a white tile.
After that, titrate with 0.1 M HCl from the burette, swirling constantly, and stop when the pink color just disappears. Record the final burette reading.
Repeat the titration until you obtain three concordant readings (readings agreeing within ±0.1 cm³).
Finally, calculate the mean volume of acid used and proceed to the calculations.

Observations

M₁ = Polarity of MOH =?

V₁ = volume of MOH taken = 10cm³

M₂ = Molarity of H Cl = 0.1M

Sr. NO.	Initial reading	Final reading	Volume of acid used
1 2 3	0.0 12.0 24.0	10.0 22.0 34.0	10.0cm³ 10.0cm³ 10.0cm³

Mean volume used = 100cm³

Calculations (using your numbers in original text: mean V = 10.0 cm³ example)

Volume of HCl used (mean) = 0.010 L (10.0 cm³)
Molarity of HCl = 0.1 mol·dm⁻³
Moles of HCl used = 0.1 × 0.010 = 0.001 mol.
Moles of MOH in 10 cm³ = 0.001 mol (1:1 ratio).
Molarity of MOH = 0.001 mol / 0.010 L = 0.1 M.
Given mass of MOH per dm³ = 4 g.
Molar mass of MOH = mass / moles per L = 4 g ÷ 0.1 mol = 40 g·mol⁻¹.
Atomic weight of M = M(MOH) − M(OH) = 40 − 17 = 23.

Result: At. wt. of M = 23

Precautions

Rinse burette and pipette properly before use.
Use phenolphthalein; read end point as the just disappearance of pink.
Take concordant titrations and calculate the mean.
Record volumes carefully to avoid calculation errors.
Ensure MOH solution concentration (4 g per dm³) is accurate.