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.
Give one major drawback of Dalton's atomic theory of matter.
Q 2.
What do we call those particles which have more or less electrons than the normal atoms ?
Q 3.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 4.
Explain with example that law of conservation of mass is valid for chemical reactions.
Q 5.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 6.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 7.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 8.
Fill in the blanks:
One mole of water contains ______________ molecules.
Q 9.
Define 'formula mass' of a compound.
Q 10.
Convert 12 g of oxygen gas into moles.
Q 11.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 12.
State Law of constant proportions. Explain with an example.
Q 13.
Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Q 14.
Magnesium is two times heavier than C-12 atom, what shall be the mass of Mg atom in terms of atomic mass units? (Given mass of C-12 atom = 12u)
Q 15.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 16.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 17.
What is the significance of a chemical symbol?
Q 18.
Why do atoms of the most of the elements not exist independently?
Q 19.
Name one element each which forms diatomic and tetra atomic molecule.
Q 20.
What is the mass of
(a) 1 mole of nitrogen atoms?
(b) 4 moles of aluminium atoms (Atomic mass of aluminium = 27)?
(c) 10 moles of sodium sulphite (Na
2SO
3)?
Q 21.
Calculate the number of molecules of sulphur (S
8) present in 16 g of solid sulphur.
Q 22.
An element Z has a valency of 3. What is the formula of oxide of Z ?
Q 23.
Calculate the mass of 3.011 x 10
atoms of carbon
Q 24.
(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 25.
Who established the two important laws of chemical combinations?
Q 26.
In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium ethanoate. Show that these observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
Q 27.
Name the international organization who approves names of elements.
Q 28.
How will you define chemical symbol?
Q 29.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 30.
What are ionic compounds?
Q 31.
Work out the formula for magnesium hydrogencarbonate.
Q 32.
Name the following compounds. Also write the symbols/formulae of the ions present in them :
(a) CuSO
Q 33.
How many moles are 3.6 g of water ?
Q 34.
Calculate the number of molecules in 4 g of oxygen.
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.
Fill in the blanks:
___________ is the combining capacity of an element.
Q 37.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 38.
Based on type of substance, how molecules are classified?
Q 39.
Give three examples of monoatomic molecules.
Q 40.
Give four examples of diatomic molecules.
Q 41.
What is the molecular mass of a substance?
Q 42.
Calculate the mass percentage of Carbon(C) , Hydrogen (H) and Oxygen (O) in one molecule of glucouse (C
6H
12O
6).
(Atomic mass of C = 12u, H = 1u and O = 16u)
Q 43.
Calculate the number of molecules of phosphorus (P
4) present in 31 gram of phosphorus.
Q 44.
Calculate the molecular masses of the following compounds :
(a) Methane, CH
Q 45.
Calculate the molecular masses of the following compounds :
(a) Methanol, CH
Q 46.
Calculate the molecular mass of chloroform (CHC1
Q 47.
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 48.
What is the mass of 0.2 mole of oxygen atoms ?
Q 49.
If one mole of nitrogen molecules weighs 28 g, calculate mass of one molecule of nitrogen in grams.
Q 50.
How many moles are there in 34.5 g of sodium ? (Atomic mass of Na = 23 u)
