Class 9th Chapter 1 Exercise Long Questions Fundamentals Of Chemistry
Q NO 1 : State and explain with examples:
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- The empirical formula of a compound
- The molecular formula of a compound
1. Empirical formula
Definition;
“The type of chemical formula which shows the smallest whole number ratio of the different atoms present in a compound is called empirical formula”.
Explanation;
Empirical formula is the shortest and simplest type of chemical formula. Empirical formula may or may not be the actual formula of a compound.
Examples
The molecular formula of benzene is C6H6 and its empirical formula is CH. So in such cases, empirical formula is not the actual formula of that compound. Similarly the molecular formula of methane is CH4 and its empirical formula is also CH4. In such cases, the empirical formula is the actual formula of that compound.
Empirical formula gives no information about total number of atoms present in a compound.
Examples
The empirical formula of glucose is CH2O. This empirical formula of glucose shows that there are one carbon atom, two hydrogen atoms and one oxygen atom present in a glucose molecule, but in actual, the glucose molecule is composed of 6 carbon atoms 12 hydrogen atoms and 6 oxygen atoms ( C6H12O6 ). The total number of atoms present in a compound are well defined by molecular formula of that compound.
Empirical formula shows the types of atoms present in a compound.
Examples
The empirical formula of glucose is CH. This empirical formula shows that glucose molecule is composed of three types of different atoms, one type is carbon-atom, second is hydrogen-atom and other is oxygen-atom.
2. Molecular formula
Definition;
“The type of chemical formula which shows the actual numbers of different atoms present in a compound is called molecular formula”.
Explanation;
Molecular formula is the actual formula of a compound as it shows the total number of atoms present in a compound.
Examples
The molecular formula of glucose is C6H12O6. This molecular formula shows that a glucose molecule is composed of 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms.
Molecular formula tells about the different types of atoms present in a compound.
Examples
The molecular formula of acetic acid is C2H4O2. This molecular formula shows that acetic acid is composed of three types of different atoms, one type is carbon atoms, second one is hydrogen atoms and other is oxygen atoms.
Molecular formula shows the ratio of the different atoms present in a compound.
Examples
The molecular formula of glucose is C6H12O6. This molecular formula shows that glucose molecule is composed of 6-carbon atoms, 12-hydrogen atoms and 6-oxygen atoms. So, the ratio of these atoms in glucose molecule is 6:12:6 .
Examples Of Empirical formula and Molecular formula ;
Following are the examples of empirical formula and molecular formula.
A) A compound may have different molecular formula from empirical formula.
1) Glucose
Glucose molecule have different molecular formula and empirical formula. The molecular formula of glucose is C6H12O6 and the empirical formula of glucose is CH2O.
2 ) Disulfur dioxide
Disulphur dioxide is a chemical compound. Its molecular formula is S2O2 and empirical formula is SO.
3 ) Benzene
Benzene is an aromatic compound. The molecular formula of benzene is C6H6. Its empirical formula is CH.
B) A compound may have same molecular formula and empirical formula. Some examples of such compounds are given below.
1 ) Water
Water is a molecule with same molecular formula (H2O) and empirical formula (H2O).
2 ) Methane
Methane is an organic compound. Its molecular formula is CH4 and its empirical formula is also CH4.
3 ) Ammonia
Ammonia molecule also have same molecular formula (NH3) and empirical formula (NH3 ).
