Question:
A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.
Answer:
Given, mass of boron = 0.096 g
mass of the oxygen = 0.144g
mass of the sample compound (boron+oxygen) = 0.24 g
According to Law of definite proportions, boron and oxygen are in fixed ratio in the given compound.= 0.096:0.0144 = 2:3
⇒ % of boron = mass of boron × 100 / mass of compound = 0.096 × 100/0.24 = 40%and % of oxygen = mass oxygen × 100 / mass of compound = 0.144 × 100/0.24 = 60%
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.
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 4.
Explain with example that law of conservation of mass is valid for chemical reactions.
Q 5.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 6.
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 7.
What do we call those particles which have more or less electrons than the normal atoms ?
Q 8.
Fill in the blanks:
One mole of water contains ______________ molecules.
Q 9.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 10.
What is gram-atomic mass of an element?
Q 11.
Convert 12 g of oxygen gas into moles.
Q 12.
How many atoms are there in 0.25 mole of hydrogen ?
Q 13.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 14.
What is the chemical symbol for iron?
Q 15.
What is the atomic mass unit?
Q 16.
Based on type of substance, how molecules are classified?
Q 17.
Give four examples of diatomic molecules.
Q 18.
Name one element each which forms diatomic and tetra atomic molecule.
Q 19.
Give one major drawback of Dalton's atomic theory of matter.
Q 20.
What is the mass of 0.2 mole of oxygen atoms ?
Q 21.
What is the law of conservation of mass?
Q 22.
Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Q 23.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 24.
What is the molecular mass of a substance?
Q 25.
What are ionic compounds?
Q 26.
Name one element which forms diatomic and triatomic molecule.
Q 27.
Define mole. What is its significance?
Q 28.
Find out number of atoms in 15 moles of He.
Q 29.
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Q 30.
What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.
Q 31.
Calculate the mass of 3.011 x 10
atoms of carbon
Q 32.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom 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.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 35.
Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Q 36.
What is the significance of a chemical symbol?
Q 37.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 38.
Define molecule. What are its important properties?
Q 39.
Based on atomicity, how molecules are categorized?
Q 40.
What are polyatomic ions? Give examples?
Q 41.
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 42.
Calculate the molecular masses of the following :
(a) Hydrogen, H
Q 43.
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 44.
How many atoms are present in one gram atomic mass of a substance ?
Q 45.
Find the mass of 2 moles of nitrogen atoms.
Q 46.
State Law of constant proportions. Explain with an example.
Q 47.
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 48.
Fill in the blanks:
Mass of 2 Hydrogen atoms is __________.
Q 49.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
Q 50.
Give three examples of monoatomic molecules.
