Question:
What are the laws of chemical combinations?
Answer:
These are group of laws which describe how different elements and compounds combine together to form new compounds. Most of these were established based on chemical experimental results. These laws are:
- Law of Conservation of Mass
- Law of Constant composition (or definite proportions)
- Law of Multiple proportions
- Law of reciprocal proportions
- Law of Combining Volumes (Gay Lussac's law of Gaseous Volumes)
- Avogadro Law
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.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 5.
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 6.
What do we call those particles which have more or less electrons than the normal atoms ?
Q 7.
Explain with example that law of conservation of mass is valid for chemical reactions.
Q 8.
Fill in the blanks:
One mole of water contains ______________ molecules.
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 chemical symbol for iron?
Q 13.
What is the atomic mass unit?
Q 14.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 15.
Give four examples of diatomic molecules.
Q 16.
Name one element each which forms diatomic and tetra atomic molecule.
Q 17.
Give one major drawback of Dalton's atomic theory of matter.
Q 18.
How many atoms are there in 0.25 mole of hydrogen ?
Q 19.
Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Q 20.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 21.
Based on type of substance, how molecules are classified?
Q 22.
What is the molecular mass of a substance?
Q 23.
What are ionic compounds?
Q 24.
Define mole. What is its significance?
Q 25.
Find out number of atoms in 15 moles of He.
Q 26.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 27.
What is the law of conservation of mass?
Q 28.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 29.
Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Q 30.
What is the significance of a chemical symbol?
Q 31.
Define molecule. What are its important properties?
Q 32.
Based on atomicity, how molecules are categorized?
Q 33.
Name one element which forms diatomic and triatomic molecule.
Q 34.
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 35.
Calculate the molecular masses of the following :
(a) Hydrogen, H
Q 36.
What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.
Q 37.
What is the mass of 0.2 mole of oxygen atoms ?
Q 38.
Calculate the mass of 3.011 x 10
atoms of carbon
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 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 41.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 42.
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Q 43.
How many atoms are present in one gram atomic mass of a substance ?
Q 44.
What name is given to the number 6.022 x 10
Q 45.
Calculate the number of molecules in 4 g of oxygen.
Q 46.
If 12 g of carbon is burnt in the presence of 32 g of oxygen, how much carbon dioxide will be formed?
Q 47.
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.
Q 48.
Fill in the blanks:
Mass of 2 Hydrogen atoms is __________.
Q 49.
Why is it not possible to see an atom with naked eyes?
Q 50.
Name the international organization who approves names of elements.
