Calculate the molarity of a solution of ethanol in water, in which the mole fraction of ethanol is 0.040 (assume the density of water to be one).
Solution and Explanation
Mole fraction of C2H5OH = \(\frac {\text {Number\ of \ moles\ of}\ C_2H_5OH}{\text {Number\ of \ Moles\ of\ Solution}}\)
\(0.040 = \frac {n_{C_2H_5OH} }{ n_{C_2H_5OH} + n_{H_2O}} \) ......(1)
Number of moles present in 1 L water:
\(n_{H_2O} = \frac {1000\ g }{8 \ g\ mol^{-1}}\)
\(n_{H_2O} = 55.55\ mol\)
Substituting the value of nH2O in equation (1),
\(\frac {n_{C_2H_5OH}}{{ n_{C_2H_5OH}}} + 55.55 = 0.040\)
\(n_{C_2H_5OH} = 0.04n_{C_2H_5OH} + (0.040).(55.55)\)
\(0.96n_{C_2H_5OH} = 2.222\ mol\)
\(n_{C_2H_5OH} = \frac {2.222 }{ 0.96} \ mol\)
\(n_{C_2H_5OH} = 2.314 \ mol\)
∴ Molarity of solution = \(\frac {2.314\ mol }{1 \ L}\) = \(2.314\ M\)
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Chemistry is a vast subject and for understanding its significance we can take help of following points:
- Chemistry plays an important role in understanding various subjects like physics, geology and biology.
- Chemistry is a core branch of science that explains us about the various compositional properties and interaction of matter. It also helps to understand various chemical reactions.
- Chemistry is important in order to understand the behaviour of fertilizers, alkenes, acids, salts, dyes, polymers, drugs, soaps and alloys in organic and inorganic chemistry.
- Chemistry plays an important role in various fields like healthcare, industrial, research, food, and farm activities.
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Classification of Matter
There are two ways of classifying the matter:
(A) Physical Classification:
Matter can exist in three physical states:
- Solids - have definite volume and definite shape
- Liquids - have definite volume but not definite shape.
- Gases - have neither definite volume nor definite shape.
(B) Chemical Classification:
Based upon the composition, matter can be divided into two main types:
- Pure Substances are defined as a single substance (or matter) which cannot be separated by simple physical methods. Pure substances can be further classified as (i) Elements (ii) Compounds
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