Victor Meyer Method

As stated above, the Victor Meyor method formula is a unit of measurement for vapour density or molecular mass in volatile organic compounds. In a device known as a Victor Meyer tube, a known mass of the substance is vaporised. The sample produces vapours that displace an equal volume of air into a graduated tube. After that, the volume of vapour is calculated and lowered to STP. 

The above process is done with the help of the Victor Meyer apparatus, which was invented by the German chemist Viktor Meyer, who was a significant contributor to both organic and inorganic chemistry.

Victor Meyer Experiment

This experiment is called the determination of molecular mass by the Victor Meyor method formula. Before moving on to the experiment, let’s first learn about the apparatus used to carry this process. The equipment consists of an inner Victor Meyer’s tube with a bulb at the lower end. The tube’s upper end contains a side tube that goes to a water-filled trough. The tube of Victor Meyer is encased in an outer jacket. A liquid is poured in the outer jacket that boils at a temperature at least 30K higher than the subject under investigation. When a glass bottle containing the item under examination is dropped to it, a small amount of glass-wool or asbestos pad covers the lower end of the Victor Meyer’s tube to prevent breakage.

1. Principle

A known mass of a volatile liquid or solid is transformed into its vapour using this process, which involves heating it in a Victor-tube. The vapour displaces the same amount of air as it does. At the experimental temperature and pressure, the volume of air displaced by the vapour is measured. After that, the volume of vapour at STP is computed. The mass of the vapour at S.T.P. is computed as 2.24 x 10⁻²m³. The molecular mass of the material is represented by this number.

2. Procedure

After the liquid in the outer jacket has boiled and no more air escapes from the side tube, a graded tube filled with water is inverted and dipped in a trough full of water. In a small stoppered bottle, a little amount of substance is precisely weighed before being quickly put into the heated Victor-Meyer tube and corked.

Blow out the cork and displace an equal volume of air into the graduated tube when the bottle lands on the asbestos pad and thus its components transform to vapour. By removing the graduated tube and inserting it in a jar full of water after sealing its mouth with the thumb, the volume of air in it may be determined. When the water levels outside and within the tube are equal, the volume of air displaced is measured. The temperature and pressure in the laboratory are then recorded.

3. Calculations

Let’s understand the Victor Meyer Method formula –

wg = weight of the volatile substance

V₁ m³ = Volume of air displaced = Volume of vapour

T₁ K = the temperature in the laboratory.

Assume that the atmospheric pressure is P.

At T₁ K, dry vapour pressure = atmospheric pressure – aqueous tension At that temperature, the aqueous tension should be p Nm⁻²

P₁ = [P-p] = pressure of dry vapour

T₀ = 273 K is the standard temperature.

P₀ = 1.013 x 105 Nm⁻² is the standard pressure.

Allow V₀ m³ for the volume of vapour at normal temperature and pressure.

Now, from the gas equation –

P₀V₀/  T₀  =  P₁ V₁ / T₁

V₀   =  (P₁ V₁ / T₁) x (T₀/ P₀)

The mass of 2.24 x 10⁻²  of the vapour at STP

= 2.24 x 10⁻² x W / V₀

And hence,

Molecular mass  =  2 x vapour density

Vapour density = Molecular mass / 2

Merits and Demerits of Victor Meyer Method –

The merit of Victor Meyer Method formula is very simple to execute and requires a very small quantity of sample.

The demerits of Victor Meyer Method formula is that the method is applicable for volatile liquid only. Also, it is not applicable to volatile substances which are soluble in water. There can be the issue of inaccuracy due to manual handling and the method is unused for those substances that undergo thermal decomposition.

Victor Meyer test for alcohols

Victor Meyer is one of the key tests to distinguish among primary, secondary and tertiary types of alcohol. But before diving into the test, let’s see what are the differences between these alcohols.

1. Primary Alcohol – Here the carbon atom bonded with –OH group which is further bonded with one or non other carbon atom. For example – Methanol.

2. Secondary Alcohol – Here the carbon atom bonded with –OH group which is further bonded with two other carbon atoms. For example – Propan-2-ol.

3. Tertiary Alcohol – Here the carbon atom bonded with –OH group which is further bonded with three other carbon atoms. For example – Methyl propan-2-ol.

Victor Meyer Method formula –

Alcohol is first treated with P and I₂ to produce iodoalkane, which is then treated with AgNO₂ (silver nitrate) to produce nitroalkane in Victor Meyer’s process. The nitroalkane produced is then treated with nitrous acid (a combination of NaNO₂ and dilute HCl) before being turned alkaline with KOH and the colour noticed. If the resultant colour is:

Red Colour – Primary Alcohol

Blue Colour – Secondary Alcohol

No Colour – Tertiary Alcohol

Conclusion

The Victor Meyer method was invented by the German chemist Viktor Meyer and can be used to determine the molecular weight or vapour densities of volatile liquids through an experiment which is explained above. The Victor Meyer method formula is an important test for the determination of alcohol into primary, secondary, and tertiary types, which is carried out again in an experiment.

Though the method is very simple to carry out, it does have certain limitations, such as the fact that manual handling can lead to certain errors and that it is applicable for volatile liquids