Question:
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Answer:
The postulate of Dalton's atomic theory that explains the law of definite proportions is:
The relative number and kinds of atoms are constant in a given compound.
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.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 4.
How many atoms are there in 0.25 mole of hydrogen ?
Q 5.
Write the chemical symbols of the following:
(i) Gold
(ii) Iron
(iii) Chlorine
(iv) Mercury
Q 6.
Name one element each which forms diatomic and tetra atomic molecule.
Q 7.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 8.
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 9.
Name the international organization who approves names of elements.
Q 10.
Define 'formula mass' of a compound.
Q 11.
Who established the two important laws of chemical combinations?
Q 12.
What is the chemical symbol for iron?
Q 13.
If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Q 14.
Write the formulae of the following compounds. Also name the elements present in them.
(a) Water
(b) Ammonia
(c) Methane
(d) Sulphur dioxide
(f) Ethanol
Q 15.
State Law of constant proportions. Explain with an example.
Q 16.
Fill in the blanks:
The mass of 5 moles of ammonia (NH
3) is __________.
Q 17.
What are polyatomic ions? Give examples?
Q 18.
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 19.
What are the postulates of Dalton's atomic theory?
Q 20.
Define molecule. What are its important properties?
Q 21.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 22.
Give four examples of diatomic molecules.
Q 23.
Fill in the blanks:
___________ is the combining capacity of an element.
Q 24.
Which element has the smallest atom in size?
Q 25.
Find out number of atoms in 15 moles of He.
Q 26.
Calculate the molecular mass of chloroform (CHC1
Q 27.
What is the numerical value of Avogadro number ?
Q 28.
Calculate the mass of 3.011 x 10
atoms of carbon
Q 29.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 30.
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 31.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 32.
Fill in the blanks:
The mass of 1 mole of a substance is called its _____________.
Q 33.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 34.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 36.
Write down the names of compounds represented by the following formulae:
(i) Al
2(SO
4)
3 (ii) CaCl
2 (iii) K
2SO
4 (iv) KNO
3 (v) CaCO
3
Q 37.
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 38.
Calculate the number of molecules of sulphur (S
8) present in 16 g of solid sulphur.
Q 39.
State whether the following statement is true or false :The symbol of element cobalt is CO.
Q 40.
How many atoms are present in one gram atomic mass of a substance ?
Q 41.
Magnesium and oxygen combine in the ratio of 3 : 2 by mass to form magnesium oxide. How much oxygen is required to react completely with 12 g of magnesium?
Q 42.
Fill in the blanks:
Atomic radius is measured in __________.
Q 43.
What is the significance of a chemical symbol?
Q 44.
What is the atomic mass unit?
Q 45.
Based on type of substance, how molecules are classified?
Q 46.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
Q 48.
Give examples of triatomic molecules.
Q 49.
Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide
Q 50.
Write the chemical formulae of the following. Also identify the ions present.
(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate
(d) Aluminium chloride
(e) Calcium carbonate.
