Question:
What is the atomic mass unit?
Answer:
The mass equal to 1/12th of the mass of 126C atom is called the one atomic mass unit. It is 1.66 × 10-27 kg. It is represented by symbol 'u' (older symbol 'amu').
1 u = 1/12th of the mass of carbon-12 atom.
Atoms and Molecules
Q 1.
Define 'formula mass' of a compound.
Q 2.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 3.
Fill in the blanks:
One mole of water contains ______________ molecules.
Q 4.
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 5.
What do we call those particles which have more or less electrons than the normal atoms ?
Q 6.
Explain with example that law of conservation of mass is valid for chemical reactions.
Q 7.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 8.
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 9.
What is gram-atomic mass of an element?
Q 10.
Convert 12 g of oxygen gas into moles.
Q 11.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 12.
What is the atomic mass unit?
Q 13.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 14.
Give one major drawback of Dalton's atomic theory of matter.
Q 15.
How many atoms are there in 0.25 mole of hydrogen ?
Q 16.
What is the law of conservation of mass?
Q 17.
What is the chemical symbol for iron?
Q 18.
Based on type of substance, how molecules are classified?
Q 19.
Give four examples of diatomic molecules.
Q 20.
Name one element each which forms diatomic and tetra atomic molecule.
Q 21.
Name one element which forms diatomic and triatomic molecule.
Q 22.
Find out number of atoms in 15 moles of He.
Q 23.
What is the mass of 0.2 mole of oxygen atoms ?
Q 24.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 25.
Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Q 26.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 27.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
Q 28.
Based on atomicity, how molecules are categorized?
Q 29.
What is the molecular mass of a substance?
Q 30.
What are ionic compounds?
Q 31.
Define mole. What is its significance?
Q 32.
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Q 33.
Calculate the molecular masses of the following :
(a) Hydrogen, H
Q 34.
State whether the following statements are true or false :
(a)A sodium ion has positive charge because it has more protons than a neutral atom
(b)A chloride ion has negative charge because it has more electrons than a neutral atom.
Q 35.
What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.
Q 36.
How many atoms are present in one gram atomic mass of a substance ?
Q 37.
Calculate the mass of 3.011 x 10
atoms of carbon
Q 38.
State Law of constant proportions. Explain with an example.
Q 39.
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 40.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 41.
Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Q 42.
What is the significance of a chemical symbol?
Q 43.
Can atoms of an element exist independently? Give examples of elements which exist in atomic form. Give examples of elements that do not exist in atomic form.
Q 44.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 45.
Define molecule. What are its important properties?
Q 46.
What are polyatomic ions? Give examples?
Q 47.
Calculate the number of aluminium ions present in 0.051 g of aluminium oxide.
(
Hint: The mass of an ion is the same as that of an atom of the same element. Atomic mass of Al = 27 u)
Q 48.
Name the unit in which the radius of an atom is usually expressed.
Q 49.
Calculate the molecular mass of hydrogen bromide (HBr).
(Atomic masses: H=1; Br= 80 U)
Q 50.
What is the numerical value of Avogadro number ?
