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.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 2.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 3.
What is gram-atomic mass of an element?
Q 4.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 5.
Define 'formula mass' of a compound.
Q 6.
What are polyatomic ions? Give examples?
Q 7.
If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Q 8.
What are the postulates of Dalton's atomic theory?
Q 9.
Which of the following statements is NOT true about an atom?
(a) Atoms are the building blocks from which molecules and ions are formed.
(b) Atoms cannot exist independently.
(c) Atoms are neutral in nature
(d) Atoms combine together to form matter that we can see, feel or touch.
Q 10.
Fill in the blanks:
The mass of 1 mole of a substance is called its _____________.
Q 11.
Give four examples of diatomic molecules.
Q 12.
Fill in the blanks:
Atomic radius is measured in __________.
Q 13.
What is the chemical symbol for iron?
Q 14.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 15.
What are the building blocks of matter ?
Q 16.
(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 17.
What is the law of conservation of mass?
Q 18.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 19.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 20.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 21.
Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide
Q 22.
Define mole. What is its significance?
Q 23.
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Q 24.
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 25.
How many atoms are there in 0.25 mole of hydrogen ?
Q 26.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 28.
What are ionic compounds?
Q 29.
What is meant by atomicity ? Explain with two
Q 30.
Work out the formula for magnesium hydrogencarbonate.
Q 31.
How many atoms are present in one gram atomic mass of a substance ?
Q 32.
Calculate the number of molecules in 4 g of oxygen.
Q 33.
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 34.
Fill in the blanks:
According to Dalton's atomic theory, atoms of different elements differ in ______, size and chemical properties.
Q 35.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 37.
Calculate the number of molecules of sulphur (S
8) present in 16 g of solid sulphur.
Q 38.
What is meant by the symbol of an element ? Explain with examples.
Q 39.
Calculate the molecular masses of the following compounds :
(a) Methanol, CH
Q 40.
Calculate the molecular mass of hydrogen bromide (HBr).
(Atomic masses: H=1; Br= 80 U)
Q 41.
Write down the formulae for the following compounds :
(a) Calcium oxide
(b) Magnesium hydroxide
Q 42.
What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.
Q 43.
What is the numerical value of Avogadro number ?
Q 44.
Convert 12 g of oxygen gas into moles.
Q 45.
If one mole of nitrogen molecules weighs 28 g, calculate mass of one molecule of nitrogen in grams.
Q 46.
Calculate the mass of 3.011 x 10
atoms of carbon
Q 47.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 48.
(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 49.
(a) What is meant by the 'molar mass'of a substance ? State the unit in which molar mass usually expressed.
(b) Calulate the molar masses of the following substances. Write the results with proper units
(1) Ozone molecule, O
Q 50.
State Law of constant proportions. Explain with an example.
