Chem Notes 1st Year Chap 1
Important Questions
Q Law of conservation of mass has to be obeyed during the stoichiometric calculations.
Ans: Stoichiometric calculation are base upon the balanced chemical equation so the number of moles of the reactant in equal to the number of moles of product. As the numbers of moles of atoms are equal hence their masses should be equal in reactant and product which is according to the law conservation of masses other wise the calculation are not possible.
Q Many Chemical Reactions taking place in our surrounding involve limiting reactant.
Ans: Many chemical reactions taking place in our surrounding involves the limiting reactant. If it is not so the reactions will go countinously and would never stop. But due to this limiting reactant the reaction stops after complete consumption of limiting reactant.
For Example, when the wood burns it reacts with the oxygen of air which is in excess. But after complete consumption of the wood the fire extinguishes.
Q Neon individual Neon atom in the sample of the elements has masses of 20.18 amu.
Ans: Neon has three isotopes which have atomic masses and having relative abundance of 90.92% 0.26% and 8.82% respectively in the nature 20.18 amu is the relative atomic mass of Neon i.e the average atomic mass of all the three isotopes of neon. this is the that no individual Neon atom in the sample of the element has a mass of 20.18 amu exactly.
Q Concept of limiting reactant is not applicable to the reversible reactions. Explain it.
Ans: The concept of limiting reactant is not applicable to the reversible reactions, because certain amunts of each reactant is left behind at the aquilibrium state and thus any reactant is not consumed completely and cannot be considered as the limiting reactant of the ractions.
Q Define the Stoichiometry. Give the assumptions for the Stoichiometry calculations. Mention two important laws which help in stoichiometric calculation.
Ans: The branch of physical Chemistry that deals with the quantitative study of quantitative relationship between the reactants and products as given by balanced chemical equation and amounts of reactant are called stoichiometric amount.
Assumption of Stoichiometry :
All the reactant are the completely changed in to the products.
The reaction is not reversible.
While doing calculations law of conservation and law of definite proportions are obeyed.
There is no side reaction.
Laws Of Stoichiometry:
Law of conservation of mass.
Law of definite proportion.
Q Define limiting reactant. How it can determined.
Ans: It can be defined as
The reactant which controls the amount of product formed in a chemical equation.
Determination of Limiting Reactants:
Determine the numbers of moles of each reactant and product in the balanced chemical equation.
Find the numbers of moles of required product from the numbers of moles of each reactant with the help of balanced chemical equation.
Identify the reactant which produces the least amount of product as limiting reactant.
Q Why the actual yield is less than theoretical yield ?
Ans: In most of chemical reactions the actual yield is less than theoretical yield because following reasons:
By product obtained in the side reaction
Reaction may be reversible
Mechanical loss of product due to filtration purification crystallization etc.
Unskilled workers.
Q What is Spectrum of mass Spectrograph ?
Ans: A graph between m/e of the positive ions as abscissa (X-axis) and the relative abundance of the isotopes as ordinate (Y-axis) is called the mass spectrum.
Q Mg twice heavier than the carbon atom. Justify
Ans: Atomic mass is the mass of an atom of element which is obtained after comparing which the mass of carbon-12. the atomic mass of Mg is 24 amu where as the atomic mass of carbon is 12 amu. As the atomic mass of Mg is double than that of carbon therefore Mg atom is twice heavier than the carbon.
Q 23g of sodium and 238g of Uranium have equal numbers of atoms .
Ans: 23g of sodium is equal to the one mole of sodium and 238g of uranium also equals one mole of Uranium and one mole contain 6.022 Multiply 10 raise power 23.
Therefore 23g of sodium and 238 g uranium have equal numbers of atoms.
Q What is an electrometer ?
Ans: It is an ion collector in the mass spectrograph which is produces the electrical current when the positive molecular ions strike on it. The Current strength produced measures the relative abundance of isotopes.
Q Law of conservation of mass has to be obeyed during the stoichiometric calculations.
Ans: Stoichiometric calculation are base upon the balanced chemical equation so the number of moles of the reactant in equal to the number of moles of product. As the numbers of moles of atoms are equal hence their masses should be equal in reactant and product which is according to the law conservation of masses other wise the calculation are not possible.
Q Many Chemical Reactions taking place in our surrounding involve limiting reactant.
Ans: Many chemical reactions taking place in our surrounding involves the limiting reactant. If it is not so the reactions will go countinously and would never stop. But due to this limiting reactant the reaction stops after complete consumption of limiting reactant.
For Example, when the wood burns it reacts with the oxygen of air which is in excess. But after complete consumption of the wood the fire extinguishes.
Q Neon individual Neon atom in the sample of the elements has masses of 20.18 amu.
Ans: Neon has three isotopes which have atomic masses and having relative abundance of 90.92% 0.26% and 8.82% respectively in the nature 20.18 amu is the relative atomic mass of Neon i.e the average atomic mass of all the three isotopes of neon. this is the that no individual Neon atom in the sample of the element has a mass of 20.18 amu exactly.
Q Concept of limiting reactant is not applicable to the reversible reactions. Explain it.
Ans: The concept of limiting reactant is not applicable to the reversible reactions, because certain amunts of each reactant is left behind at the aquilibrium state and thus any reactant is not consumed completely and cannot be considered as the limiting reactant of the ractions.
Q Define the Stoichiometry. Give the assumptions for the Stoichiometry calculations. Mention two important laws which help in stoichiometric calculation.
Ans: The branch of physical Chemistry that deals with the quantitative study of quantitative relationship between the reactants and products as given by balanced chemical equation and amounts of reactant are called stoichiometric amount.
Assumption of Stoichiometry :
All the reactant are the completely changed in to the products.
The reaction is not reversible.
While doing calculations law of conservation and law of definite proportions are obeyed.
There is no side reaction.
Laws Of Stoichiometry:
Law of conservation of mass.
Law of definite proportion.
Q Define limiting reactant. How it can determined.
Ans: It can be defined as
The reactant which controls the amount of product formed in a chemical equation.
Determination of Limiting Reactants:
Determine the numbers of moles of each reactant and product in the balanced chemical equation.
Find the numbers of moles of required product from the numbers of moles of each reactant with the help of balanced chemical equation.
Identify the reactant which produces the least amount of product as limiting reactant.
Q Why the actual yield is less than theoretical yield ?
Ans: In most of chemical reactions the actual yield is less than theoretical yield because following reasons:
By product obtained in the side reaction
Reaction may be reversible
Mechanical loss of product due to filtration purification crystallization etc.
Unskilled workers.
Q What is Spectrum of mass Spectrograph ?
Ans: A graph between m/e of the positive ions as abscissa (X-axis) and the relative abundance of the isotopes as ordinate (Y-axis) is called the mass spectrum.
Q Mg twice heavier than the carbon atom. Justify
Ans: Atomic mass is the mass of an atom of element which is obtained after comparing which the mass of carbon-12. the atomic mass of Mg is 24 amu where as the atomic mass of carbon is 12 amu. As the atomic mass of Mg is double than that of carbon therefore Mg atom is twice heavier than the carbon.
Q 23g of sodium and 238g of Uranium have equal numbers of atoms .
Ans: 23g of sodium is equal to the one mole of sodium and 238g of uranium also equals one mole of Uranium and one mole contain 6.022 Multiply 10 raise power 23.
Therefore 23g of sodium and 238 g uranium have equal numbers of atoms.
Q What is an electrometer ?
Ans: It is an ion collector in the mass spectrograph which is produces the electrical current when the positive molecular ions strike on it. The Current strength produced measures the relative abundance of isotopes.
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