Determining Molecular Masses Using Victor Meyer’s Method

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Introduction

It is counted as a standard laboratory method for determining the molecular weight of a volatile liquid. This concept was discovered by Victor Meyer. In this process, a known mass of volatile liquid or solid is put under examination and they are converted into its vapor form by heating by using Victor Meyers tube, as this tube helps in the conversion of volatile solid or liquid into vapour form. Vapor helps in the displacement of its own volume of air and the volume of air displaced at given experimental temperature and pressure is calculated. At STP ( standard temperature pressure ) i.e at  2.24x10−2m3 displaced mass of air is calculated. The value which is obtained from this process is known as the molecular mass of the substance. 


Construction

Instrumentation of this process includes an inner Victor Meyer's tube, the lower end of which is in the form of a bulb. The upper end of the tube has a side tube that leads to a trough filled with water. The tube which is known to be Victor Meyer’s tube is surrounded by a jacket from outside and a liquid is placed in an outer jacket, which usually boils at least 30k more than the substance when kept under examination. Usage of Meyers tube is used to protect instrument from outer breakage,  when a glass bottle containing the substance under examination is dropped to it


Numerical Representation of Victor Meyer Method

This method is used for the determination of the molecular mass of volatile organic compounds. Under this process, we take the known mass of the compound, and this compound is vaporized in an instrument known as Victor Meyer tube.  The amount of vapor obtained is measured and reduced to standard temperature pressure i.e STP.

Let the volume of vapors obtained at STP be V mL

22400 mL of vapors are obtained from 1 mole of a given compound.

V mL of vapors are obtained from (V/ 22400) mL of the compound

Mole= W/Mw

Therefore,

W/Mw = V/22400


Applications of Victor Meyer Method

1. Identification of Alcohols

This method is used for the identification of alcohol. From this, you can determine primary, secondary and tertiary alcohols by a change in their colors. During this process, alcohol is treated with Phosphorus triiodide which is further treated with Silver nitric oxide to get nitroalkane as a product. Further, this product i.e nitroalkane is treated with nitrous acid which is obtained by reaction of NaNO2 and HCl. The last wrestling solution is treated with KOH and the required color is obtained. If it is red the color indicates primary alcohol, if blue it indicates secondary alcohol and if no color is seen then indicates tertiary alcohol. 

2. Determination of Empirical Formula and Molecular Formula

This method is used for the determination of both empirical as well as molecular formula, by using the given method. An empirical formula tells us the relative ratios of different atoms in a compound. 

Whereas to find a molecular formula, we need to know the molecular mass of the given compound. 


One Word Answer

1. Mercury forms a compound with chlorine that is 73.9% mercury and 26.1% chlorine by mass. What is the empirical formula?

Answer: Mercury dichloride

2. Which color is obtained in secondary alcohol during the alcohol detection?

Answer: Blue color

FAQs (Frequently Asked Questions)

1. Differentiate between primary, secondary and tertiary alcohol by Victor Meyer Method?

Ans. The Victor Meyer test is used to differentiate between primary, secondary and tertiary alcohol by the colour they obtain when they react with the required reagents.

Primary Alcohols – Red colour

Secondary Alcohols – Blue colour

Tertiary Alcohols – No colour is observed

2. Write a note on the instrumentation of the Victor Meyer Method?

Ans. Instrumentation of this process includes an inner Victor Meyer's tube, the lower end of which is in the form of a bulb. The upper end of the tube has a side tube that leads to a trough filled with water. The tube which is known to be Victor Meyer’s tube is surrounded by a jacket from outside and a liquid is placed in an outer jacket, which usually boils at least 30k more than the substance when kept under examination. Usage of Meyers tube to protect the instrument from outer breakage,  when a glass bottle containing the substance under examination is dropped to it.

3. How to make an empirical table of carbon’s composition is 48%, hydrogen 8%, nitrogen 28%, and oxygen 16%?

Ans. The required empirical table is drawn below:

Element

Percentage

Atomic Mass

The relative number of Atoms

Simplest Atomic Ratio

Simplest whole number Atomic Ratio

Carbon

48.0

12

48/12=4

4/1=4

4

Hydrogen

8.0

1

8/1=8

8/1=8

8

Nitrogen

28.0

14

28/14=2

2/1=2

2

Oxygen

16.0

16

16/16=1

1/1=1

1

So the obtained empirical formula is C4H8N2O.

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