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 gram-atomic mass of an element?
Q 2.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 3.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 4.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 5.
Define 'formula mass' of a compound.
Q 6.
What is the chemical symbol for iron?
Q 7.
Give four examples of diatomic molecules.
Q 8.
If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Q 9.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 10.
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 11.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 12.
What are the postulates of Dalton's atomic theory?
Q 13.
Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Q 14.
What are polyatomic ions? Give examples?
Q 15.
Calculate the molecular mass of nitric acid,HNO
Q 16.
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 17.
How many atoms are there in 0.25 mole of hydrogen ?
Q 18.
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 19.
(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 20.
Fill in the blanks:
Atomic radius is measured in __________.
Q 21.
Fill in the blanks:
The mass of 1 mole of a substance is called its _____________.
Q 22.
What are ionic compounds?
Q 23.
Define mole. What is its significance?
Q 24.
Who introduced the term 'mole' in chemistry?
Q 25.
Calculate the number of molecules of sulphur (S
8) present in 16 g of solid sulphur.
Q 26.
What are the building blocks of matter ?
Q 27.
What is meant by atomicity ? Explain with two
Q 28.
Calculate the molecular mass of hydrogen bromide (HBr).
(Atomic masses: H=1; Br= 80 U)
Q 29.
Name the following compounds. Also write the symbols/formulae of the ions present in them :
(a) CuSO
Q 30.
What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.
Q 31.
Fill in the following blanks :
(a)1 mole Contains...........atoms- molecules or ions of a substance
(b)A mole represents an..........number of Particles of a substance.
(c)60 g of carbon element are...........moles of carbon atoms.
(d) 0.5 mole of calcium element has a mass of..........
(e) 64 g of oxygen gas contains..........moles of oxygen atoms.
Q 32.
If one mole of nitrogen molecules weighs 28 g, calculate mass of one molecule of nitrogen in grams.
Q 33.
Calculate the number of molecules in 4 g of oxygen.
Q 34.
Calculate the mass in grams of 0.17 mole of hydrogen sulphide, H
Q 35.
What is the law of conservation of mass?
Q 36.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 37.
Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Q 38.
Fill in the blanks:
___________ is the combining capacity of an element.
Q 39.
Fill in the blanks:
_________ are building block of all matter.
Q 40.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 41.
Name the international organization who approves names of elements.
Q 42.
Why do atoms of the most of the elements not exist independently?
Q 43.
What is Formula Unit Mass? How it is different from molecular mass?
Q 44.
How do we know the presence of atoms if they do not exist independently for most of the elements?
Q 45.
Name one element which forms diatomic and triatomic molecule.
Q 46.
What is molar mass?
Q 47.
When 'mole' was chosen internationally standard way to express larger number of chemical units?
Q 48.
What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
Q 49.
What is meant by the symbol of an element ? Explain with examples.
Q 50.
The molecular formula of glucose is C
