Q1. 5.18g of copper metal is first converted to copper nitrate and subsequently to 6.45g CuO. In another experiment 1.10g copper gave 1.37g CuO on combustion. Show that the above data verify the law of definite proportion.
Answers
Answer:
- Chemistry
By studying the results of quantitative measurements of many reactions, it was observed that substances react according to the certain laws. Such laws are called the laws of chemical combination or the laws of Stoichiometry. In Greek, stoichion means an element and metron means to measure. So, stoichiometry means to measure an element in terms of mass, volume and molecule. The branch of physical chemistry which deals with the relationship between reactant and product in terms of mass, volume and molecule is known as law of Stoichiometry.
Law of Constant Composition
Law of Constant Composition deals with the composition of chemical compounds. This law was proposed by Joseph Louis Proust in 1799. It states that "a chemically pure compound always contains the same elements combined together in a definite proportion by their weight."
Or,
"The percentage composition of an element in a compound is always fixed."
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According to this law, a compound can be obtained from different sources, different methods of preparations but the composition of element does not vary. For example, CO₂ can be obtained by different methods;
1. By burning coke with oxygen
C + O₂ ➡ CO₂
Coke
2. By heating CaCO₃
CaCO₃ ➡ CaO + CO₂
3. By the reaction between CaCO₃ and dil. HCl
CaCO₃ + dil. HCl ➡ CaCl₂ + H₂O + CO₂
In above chemical reactions, the ratio of weight of carbon and oxygen in each CO₂ is 12:32 or 3:8 which is same.
Hence, law of constant composition is verified.
5.18 g of copper metal is first converted into copper nitrate and subsequently on ignition to give 6.45 g of CuO. In another experiment, 1.10 g of copper gave 1.37 g of CuO. Show that these data illustrates the law of constant composition.
Case I:
Weight of metal (Cu) = 5.18 g
Weight of metal oxide (CuO) = 6.45 g
Percentage of Cu,
Weight of Copper/Weight of CuO x 100%
= 5.18/6.45 x 100%
= 80.29%
Case II:
Weight of metal (Cu) = 1.10 g
Weight of metal oxide (CuO) = 1.37 g
Percentage of Cu,
Weight of Copper/Weight of CuO x 100%
= 1.10/1.37 x 100%
= 80.31%
Hence, the percentage of Cu in both cases are same which illustrates the law of constant composition.