Question:
Give an example to show Law of conservation of mass applies to physical change also.
Answer:
When ice melts into water, is a physical change. Take a piece of ice in small flask, cork it and weight it (say W
ice gm). Heat the flask gently and ice (solid) slowly melts into water (liquid). Weigh the flask again (W
water gm). It is found there is no change in the weight i.e. W
ice= W
water.
Heat(Δ)
Ice ----------➜ Water
This shows law of conservation of mass holds true for physical changes.
Atoms and Molecules
Q 1.
What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
Q 2.
Write the full form of IUPAC.
Q 3.
What name is given to the number 6.022 x 10
Q 4.
How many moles are 3.6 g of water ?
Q 5.
If one mole of nitrogen molecules weighs 28 g, calculate mass of one molecule of nitrogen in grams.
Q 6.
An element Z has a valency of 3. What is the formula of oxide of Z ?
Q 7.
What is the difference between a cation and an anion ? Explain with examples. Using this information, write down the formulae of:
(i) Sodium sulphide
(ii) Copper nitrate
Q 8.
How many moles of calcium carbonate (CaCO
Q 9.
The molecular formula of glucose is C
Q 10.
What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.
Q 11.
What is the numerical value of Avogadro number ?
Q 12.
Is there any exception to law of conservation of mass?
Q 13.
What is meant by atomicity ? Explain with two
Q 14.
What do we call those particles which are formed :
(a)by the gain of electrons by atoms ?
(b)by the loss of electrons by atoms ?
Q 15.
What is the mass of 0.2 mole of oxygen atoms ?
Q 16.
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 17.
Fill in the blanks:
The _______________ of a compound is a symbolic representation of its composition.
Q 18.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 19.
How many moles are there in 4.6 gms of Sodium(Na)?
Q 20.
Calculate the molecular mass of chloroform (CHC1
Q 21.
How many moles are there in 34.5 g of sodium ? (Atomic mass of Na = 23 u)
Q 22.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 23.
Calculate the number of molecules in 4 g of oxygen.
Q 24.
(a) Define gram atomic mass of a substance.How much is the gram atomic mass of oxygen ?
(b) How many moles of oxygen atoms are present in one mole of the following compounds ?
(i)Al
(ii) co
2(iii) C1
(iv) H
(p)A1
Q 25.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 26.
An element X has a valency of 4 whereas another element Y has a valency of 1. What will be the formula of the compound formed between X and Y ?
Q 27.
Name the following compounds. Also write the symbols/formulae of the ions present in them :
(a) CuSO
Q 28.
Calculate the mass in grams of 0.17 mole of hydrogen sulphide, H
Q 29.
Show by means of calculations that 5 moles of CO, and 5 moles of H
do not have the same mass. How much is the difference in their masses ?
Q 30.
(a) What is meant by 'a mole of carbon atoms' ?
(b)(b) Which has more atoms, 50 g of aluminium or 50 g of iron ? Illustrate your answer with the help of calculations.
(Atomic masses : A1 = 27 u ; Fe = 56 u)
Q 31.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 32.
Fill in the blanks:
Hydrogen and oxygen combines to form H
2O and H
2O
2. These two compounds obey the law of ____________________.
Q 33.
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 34.
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Q 35.
Calculate the molecular masses of the following :
(a) Hydrogen, H
Q 36.
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 37.
Name the elements water is made of. What are the valencies of these elements ? Work out the chemical formula for water.
Q 38.
Work out the formulae for the following compounds :
(a) Sodium oxide
Q 39.
Find the mass of 2 moles of nitrogen atoms.
Q 40.
(a) Define gram molecular mass of a substance. How much is the gram molecular mass of oxygen ?
(b) If sulphur exists as S8 molecules, calculate the number of moles in 100 g of sulphur.. (S = 32 u)
Q 41.
If 12 g of carbon is burnt in the presence of 32 g of oxygen, how much carbon dioxide will be formed?
Q 42.
State Law of constant proportions. Explain with an example.
Q 43.
When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is burnt in 50.00 g of oxygen? Which law of chemical combination will govern your answer?
Q 44.
What are the postulates of Dalton's atomic theory?
Q 45.
Fill in the blanks:
___________ is the combining capacity of an element.
Q 46.
Why is it not possible to see an atom with naked eyes?
Q 47.
Name the international organization who approves names of elements.
Q 48.
How will you define chemical symbol?
Q 49.
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 50.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
