Question:
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Answer:
(a) Quick lime: Calcium Oxide (CaO), Elements Present: Calcium(Ca), Oxygen(O)
(b) Hydrogen bromide: HBr, Elements Present: Hydrogen (H), Bromine(Br)
(c) Baking powder: Sodium Bicarbonate (NaHCO3) Elements Present: Sodium(Na), Hydrogen(H), Carbon(C) and Oxygen(O).
(d) Potassium sulphate: K2SO4Elements Present:Potassium(K), Sulphur(S), Oxygen(O)
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.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 6.
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 7.
Name the international organization who approves names of elements.
Q 8.
Write the chemical symbols of the following:
(i) Gold
(ii) Iron
(iii) Chlorine
(iv) Mercury
Q 9.
Name one element each which forms diatomic and tetra atomic molecule.
Q 10.
Define 'formula mass' of a compound.
Q 11.
Who established the two important laws of chemical combinations?
Q 12.
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 13.
What is the chemical symbol for iron?
Q 14.
What are polyatomic ions? Give examples?
Q 15.
If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Q 16.
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 17.
State Law of constant proportions. Explain with an example.
Q 18.
Fill in the blanks:
The mass of 5 moles of ammonia (NH
3) is __________.
Q 19.
Define molecule. What are its important properties?
Q 20.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 21.
Give four examples of diatomic molecules.
Q 22.
What are the postulates of Dalton's atomic theory?
Q 23.
Fill in the blanks:
___________ is the combining capacity of an element.
Q 24.
Find out number of atoms in 15 moles of He.
Q 25.
Calculate the molecular mass of chloroform (CHC1
Q 26.
What is the numerical value of Avogadro number ?
Q 27.
Calculate the mass of 3.011 x 10
atoms of carbon
Q 28.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 29.
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 30.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 32.
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 33.
Calculate the number of molecules of sulphur (S
8) present in 16 g of solid sulphur.
Q 34.
State whether the following statement is true or false :The symbol of element cobalt is CO.
Q 35.
How many atoms are present in one gram atomic mass of a substance ?
Q 36.
Fill in the blanks:
Atomic radius is measured in __________.
Q 37.
Fill in the blanks:
The mass of 1 mole of a substance is called its _____________.
Q 38.
What is the significance of a chemical symbol?
Q 39.
What is the atomic mass unit?
Q 40.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 41.
Based on type of substance, how molecules are classified?
Q 43.
Give examples of triatomic molecules.
Q 44.
Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide
Q 45.
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 46.
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 47.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 48.
Which element has the smallest atom in size?
Q 49.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
Q 50.
How many atoms are present in a
(i) H
2S molecule and
(ii) PO
43- ion?
