Empirical and Molecular Formulae

IMPORTANT

Empirical and Molecular Formulae: Overview

This topic covers concepts, such as, Empirical Formula, Molecular Formula, Steps Involved in Determination of Empirical Formula of a Compound & Relation between Empirical Formula and Molecular Formula etc.

Important Questions on Empirical and Molecular Formulae

HARD
IMPORTANT

An organic compound A contains 69.77% carbon, 11.63% hydrogen and the rest is oxygen. The molecular mass of the compound is 86. It does not reduce Tollen’s reagent but forms an addition product with sodium hydrogen sulphite and gives positive iodoform test. On vigorous oxidation it gives ethanoic and propanoic acids. The compound A is:

MEDIUM
IMPORTANT

An organic compound contains carbon, hydrogen and oxygen. Its elemental analysis gave C, 38.71% and H, 9.67%. The empirical formula of the compound would be:

MEDIUM
IMPORTANT

Percentage of Se in peroxidase anhydrase enzyme is   0.5% by weight   (at.wt.=78.4) then minimum molecular weight of peroxidase anhydrase enzyme is

EASY
IMPORTANT

An organic compound containing   C,HandO gave on analysis   C40%andH6.66%. Its empirical formula would be:

MEDIUM
IMPORTANT

An organic compound containing C, H and N gave the following analysis:

 C=40%;H=13.33%;N=46.67%

Its empirical formula would be:

MEDIUM
IMPORTANT

In a compound C, H, N atoms are present in the ratio 9 : 1 : 3.5 by mass. If molecular mass of the compound is 108, then molecular formula of the compound is 

MEDIUM
IMPORTANT

In a compound C, H, N atoms are present in the ratio 9 : 1 : 3.5 by mass. If molecular mass of the compound is 108, then molecular formula of the compound is 

HARD
IMPORTANT

An organic compound having molecular mass 60 u is found to contain  = 20%, H = 6.67% and N = 46.67%  rest being oxygen. On heating, it gives  NH 3 along with solid residue. The solid residue gives violet colour with alkaline copper sulphate solution. The compound is

HARD
IMPORTANT

An organic compound A, containing C, H, N and O, on analysis gives 49.32% carbon, 9.59% hydrogen and 19.18% nitrogen. A on boiling with NaOH gives of  NH3 and a salt, which on acidification gives a monobasic nitrogen-free acid B. The silver salt of B contains 59.67% silver. The structures of A and B are.

HARD
IMPORTANT

A certain hydrocarbon A was found to contain 85.7 percent carbon and 14.3 percent hydrogen. This compound consumes 1 molar equivalent of hydrogen to give a saturated hydrocarbon B. 1.00 g of hydrocarbon A just decolourised 38.05 g of a 5 percent solution (by weight) of Br2inCCl4. Compound A, on oxidation with concentrated KMnO4, gave compound C (molecular formula, C4H8O ) and acetic acid. The compound C could easily be prepared by the action of acidic aqueous mercuric sulphate on 2-butyne. The molecular formula of A, B and C are.

EASY
IMPORTANT

If two compounds have the same empirical formula but different molecular formulae, they must have

MEDIUM
IMPORTANT

2.2g of compound of phosphorus and sulphur has 1.24g of 'P' in it. Its empirical formula could be

HARD
IMPORTANT

Dieldrin, an insecticide, contains C, H, Cl and O. Combustion of 29.72 mg of Dieldrin gave 41.21 mg CO2 and 5.63 mg of H2O. In a separate analysis 25.31 mg of Dieldrin was converted into 57.13 mg AgCl. What is the empirical formula of Dieldrin?

EASY
IMPORTANT

The pair of species having same percentage of carbon is -

HARD
IMPORTANT

A compound contains 4.07% hydrogen, 24.25% carbon and 71.75% chlorine. What is its empirical formula?

HARD
IMPORTANT

What is the empirical formula of the salt? 

MEDIUM
IMPORTANT

In an ionic compound moles ratio of cation to anion is 1:2. If atomic masses of metal and non-metal respectively are 138 and 19, then correct statement is:

EASY
IMPORTANT

Which of the following is true about empirical formula and molecular formula?

HARD
IMPORTANT

For fixed mass of nitrogen in its two oxides A and B mass ratio of oxygen is 1 : 3. If in A, 7 g of N combines with 4 g of oxygen, then empirical formula of B will be:

HARD
IMPORTANT

20 ml of gas NxHy was completely decomposed bypassing electric spark through it in an eudiometer. Volume after sparking was 40 ml. This was mixed with 45 ml of O2(g) and exploded. The resulting mixture contracted to 40 ml.Molecular formula of NxHy is_____.