Analysis of Compounds, Combustion Analysis, Empirical Formula, Molecular Formula

 Analysis of Compounds:

A chemist can analyze a compound by following steps:

  •  First, which elements are present in the compound. It is called Qualitative Analysis.
  •  Second, what is the mass of each element in the given mass of the compound. It is called quantitative analysis.

  • Third, what is the percentage of each element in the compound. The number of grams of an element present in 100 grams of the compound is called Percentage Composition.

Formula:

Formulas for the analysis of a Compounds


  • Fourth, what is the empirical and Molecular formulas of the compound.


Combustion Analysis:

We can analyze a simple organic compound by combustion. It is shown below:

Diagram:

Combustion Analysis procedure, Combustion analysis steps


The weight amount of an organic compound is taken in a combustion tube. This tube is fitted in a furnace. The compound burns the presence of oxygen. The carbon is converted into CO2 and Hydrogen is converted into H2O. The CO2 absorbs in 50% KOH and H2O absorbs in Magnesium Perchlorate Mg(ClO4)2. The weights of absorbers increase. By the different methods, we find the mass of CO2 and H2O. Then we find % of carbon, Hydrogen, and Oxygen.


Formula:

Combustion Analysis




Empirical Formula:

The simplest formula which gives the smallest whole-number ratio of all atoms in a compound is called Empirical Formula.

For Example, The empirical Formula of Glucose is CH2O.

The Empirical Formula of Benzene is CH.

The Emperical Formula of Methane is CH4.


We can determine the empirical formula as follows:

  • ·         Determine the % of each element in the Compound.
  • ·         Divide % of each element by its atomic mass. It gives mole ratios of elements.
  • ·         Divide all mole ratios by the least one. It gives an atomic ratio of elements.
  • ·         If atomic ratios are in Fractions, Change them into whole numbers.
  • ·         Finally, the empirical formula of the compound is Written.

 
Molecular Formula:

The formula of a substance based on the actual molecule is called Molecular Formula.

For Example, C6H6  is the molecular formula of benzene and C6H12O6 is the molecular formula of Glucose.

A very large number of compounds have the same Empirical and Molecular Formulas. For example, H2O, CO2, NH3, HNO3, C12H22O11 etc.

The molecular formula is a simple multiple of the empirical formula.

Molecular Formula = n (Emperical Formula)

Where “n” is the ratio of molecular mass and empirical formula mass.


Formula:

Molecular Formula


If  “n”  is unity (one) then the Empirical and Molecular Formulas are the same.

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