
Dumas’ method involved the determination of nitrogen content in the organic compound in the form of:
(A)
(B)
(C) NaCN
(D)
Answer
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Hint: Dumas’ method is a method used for quantitative determination of nitrogen content. The product of this method is a mixture of gases from which a diatomic gas is isolated which has atomic number 7 and is present in abundant amounts in the earth’s atmosphere.
Complete answer:
-Dumas method is a method for quantitative determination of nitrogen in the chemical substances. In this method the given amount of substance is heated with copper oxide in the presence of atmosphere, at a temperature of 800 – 900°C. The combustion causes release of carbon dioxide ( ), water ( ) and nitrogen ( ). These gases are then passed over special columns which absorb the carbon dioxide and water. The nitrogen content is then measured by a thermal conductivity detector at the end.
-This reaction for Dumas’ method can be written as:
This mixture of gases is placed over KOH solution which absorbs .
-We will take the mass of organic compound containing N to be = m g
Volume of collected = L
Room temperature = T K
Atmospheric pressure at which this nitrogen is collected= P mm of Hg
Aqueous tension at room temperature or pressure of water vapour at room temperature = mm of Hg
Pressure of dry nitrogen will be = = mm of Hg
First we will find the volume of nitrogen at standard conditions (STP).
According to the gas law:
where (1) is for the given room conditions and (2) is for STP conditions.
Let (760 mm of Hg), and (273 K) will represent the respective conditions at STP.
This is the volume of nitrogen collected at STP conditions.
-Now we will calculate the percentage of nitrogen.
We all know that 22.4 L or 22400 at STP weighs = 28 g
So, of at STP weights = g
So, now the percentage of nitrogen will be calculated by:
% = (weight of / weight of organic compound) × 100
% =
So, the correct option is:
So, the correct answer is “Option B”.
Note: Sometimes some oxides of nitrogen are also released in the final products. These nitrogen oxides are reduced back to by passing through heated copper gauze.
All the nitrogen from the mixed products is isolated by passing it through a solution of KOH which absorbs all the and .
Also remember that the volume term in the final formula ( ) is always volume at STP conditions.
Complete answer:
-Dumas method is a method for quantitative determination of nitrogen in the chemical substances. In this method the given amount of substance is heated with copper oxide in the presence of
-This reaction for Dumas’ method can be written as:
This mixture of gases is placed over KOH solution which absorbs
-We will take the mass of organic compound containing N to be = m g
Volume of
Room temperature = T K
Atmospheric pressure at which this nitrogen is collected= P mm of Hg
Aqueous tension at room temperature or pressure of water vapour at room temperature =
Pressure of dry nitrogen will be =
First we will find the volume of nitrogen at standard conditions (STP).
According to the gas law:
where (1) is for the given room conditions and (2) is for STP conditions.
Let
This is the volume of nitrogen collected at STP conditions.
-Now we will calculate the percentage of nitrogen.
We all know that 22.4 L or 22400
So,
So, now the percentage of nitrogen will be calculated by:
% = (weight of
% =
So, the correct option is:
So, the correct answer is “Option B”.
Note: Sometimes some oxides of nitrogen are also released in the final products. These nitrogen oxides are reduced back to
All the nitrogen from the mixed products is isolated by passing it through a solution of KOH which absorbs all the
Also remember that the volume term in the final formula (
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