Question:
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Answer:
The theory that 'all matter is made up of very tiny indivisible particles (atoms)' is called atomic theory of matter. Dalton put forward his atomic theory of matter in 1808.
1.All the matter is made up of very small particles called 'atoms'.
2.Atoms cannot be divided.
3.Atoms can neither be created nor destroyed.
4.Atoms are of various kinds. There are as many kinds of atoms as are elements.
5.All the atoms of a given element are identical in every respect, having the same mass, size and chemical properties.
6.Atoms of different elements differ in mass, size and chemical properties.
7.Chemical combination between two (or more) elements consists in the joining together of atoms of these elements to form molecules of compounds.
Atoms and Molecules
Q 1.
What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
Q 2.
An element Z has a valency of 3. What is the formula of oxide of Z ?
Q 3.
What name is given to the number 6.022 x 10
Q 4.
Write the full form of IUPAC.
Q 5.
The molecular formula of glucose is C
Q 6.
What is the numerical value of Avogadro number ?
Q 7.
How many moles are 3.6 g of water ?
Q 8.
If one mole of nitrogen molecules weighs 28 g, calculate mass of one molecule of nitrogen in grams.
Q 9.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 10.
Is there any exception to law of conservation of mass?
Q 11.
Fill in the blanks:
The _______________ of a compound is a symbolic representation of its composition.
Q 12.
What is the difference between a cation and an anion ? Explain with examples. Using this information, write down the formulae of:
(i) Sodium sulphide
(ii) Copper nitrate
Q 13.
What is the mass of 0.2 mole of oxygen atoms ?
Q 14.
How many moles of calcium carbonate (CaCO
Q 15.
How many moles are there in 34.5 g of sodium ? (Atomic mass of Na = 23 u)
Q 16.
Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?
Q 17.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 18.
What is meant by atomicity ? Explain with two
Q 19.
What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.
Q 20.
Show by means of calculations that 5 moles of CO, and 5 moles of H
do not have the same mass. How much is the difference in their masses ?
Q 21.
(a) What is meant by 'a mole of carbon atoms' ?
(b)(b) Which has more atoms, 50 g of aluminium or 50 g of iron ? Illustrate your answer with the help of calculations.
(Atomic masses : A1 = 27 u ; Fe = 56 u)
Q 22.
Fill in the blanks:
Hydrogen and oxygen combines to form H
2O and H
2O
2. These two compounds obey the law of ____________________.
Q 23.
How many moles are there in 4.6 gms of Sodium(Na)?
Q 24.
Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23 u, Fe = 56 u)?
Q 25.
Calculate the molecular masses of the following :
(a) Hydrogen, H
Q 26.
What do we call those particles which are formed :
(a)by the gain of electrons by atoms ?
(b)by the loss of electrons by atoms ?
Q 27.
Work out the formulae for the following compounds :
(a) Sodium oxide
Q 28.
Calculate the number of molecules in 4 g of oxygen.
Q 29.
Calculate the mass in grams of 0.17 mole of hydrogen sulphide, H
Q 30.
What are the postulates of Dalton's atomic theory?
Q 31.
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Q 32.
Calculate the molecular mass of chloroform (CHC1
Q 33.
State whether the following statements are true or false :
(a)A sodium ion has positive charge because it has more protons than a neutral atom
(b)A chloride ion has negative charge because it has more electrons than a neutral atom.
Q 34.
An element X has a valency of 4 whereas another element Y has a valency of 1. What will be the formula of the compound formed between X and Y ?
Q 35.
(a) Define gram atomic mass of a substance.How much is the gram atomic mass of oxygen ?
(b) How many moles of oxygen atoms are present in one mole of the following compounds ?
(i)Al
(ii) co
2(iii) C1
(iv) H
(p)A1
Q 36.
State Law of constant proportions. Explain with an example.
Q 37.
Fill in the blanks:
_________ are building block of all matter.
Q 38.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 39.
How will you define chemical symbol?
Q 40.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 41.
Calculate the molecular masses of H
2, O
2, Cl
2, CO
2, CH
4, C
2H
6, C
2H
4, NH
3, CH
3OH.
Q 42.
What are the building blocks of matter ?
Q 43.
Calculate the molecular mass of ethanoic acid, CH
Q 44.
Name the elements water is made of. What are the valencies of these elements ? Work out the chemical formula for water.
Q 45.
Name the following compounds. Also write the symbols/formulae of the ions present in them :
(a) CuSO
Q 46.
(a) Define gram molecular mass of a substance. How much is the gram molecular mass of oxygen ?
(b) If sulphur exists as S8 molecules, calculate the number of moles in 100 g of sulphur.. (S = 32 u)
Q 47.
Give an example to show Law of conservation of mass applies to physical change also.
Q 48.
Explain with example that law of conservation of mass is valid for chemical reactions.
Q 49.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 50.
What is the atomic mass unit?
