Question:
State Law of constant proportions. Explain with an example.
Answer:
In a chemical substance the elements are always present in definite proportions by
mass, no matter how that chemical compound is prepared.
Example: Water always contains Hydrogen and Oxygen in the same proportion i.e. the ratio of
the mass of hydrogen to the mass of oxygen is always 1:8, whatever the source of water. Whether water comes from melting of ice or by condensation of steam (physical changes) or by it is produced through chemical reactions.
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.
An element Z has a valency of 3. What is the formula of oxide of Z ?
Q 4.
What is the numerical value of Avogadro number ?
Q 5.
What name is given to the number 6.022 x 10
Q 6.
If one mole of nitrogen molecules weighs 28 g, calculate mass of one molecule of nitrogen in grams.
Q 7.
The molecular formula of glucose is C
Q 8.
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 9.
How many moles are 3.6 g of water ?
Q 10.
What is the mass of 0.2 mole of oxygen atoms ?
Q 11.
How many moles are there in 34.5 g of sodium ? (Atomic mass of Na = 23 u)
Q 12.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 13.
Is there any exception to law of conservation of mass?
Q 14.
Fill in the blanks:
The _______________ of a compound is a symbolic representation of its composition.
Q 15.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 16.
What is meant by atomicity ? Explain with two
Q 17.
What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.
Q 18.
How many moles of calcium carbonate (CaCO
Q 19.
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 20.
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 21.
How many moles are there in 4.6 gms of Sodium(Na)?
Q 22.
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 23.
Calculate the mass in grams of 0.17 mole of hydrogen sulphide, H
Q 24.
(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 25.
Fill in the blanks:
Hydrogen and oxygen combines to form H
2O and H
2O
2. These two compounds obey the law of ____________________.
Q 26.
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 27.
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Q 28.
Calculate the molecular masses of the following :
(a) Hydrogen, H
Q 29.
Calculate the molecular mass of chloroform (CHC1
Q 30.
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 31.
Work out the formulae for the following compounds :
(a) Sodium oxide
Q 32.
Calculate the number of molecules in 4 g of oxygen.
Q 33.
(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 34.
What are the postulates of Dalton's atomic theory?
Q 35.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
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.
Name the following compounds. Also write the symbols/formulae of the ions present in them :
(a) CuSO
Q 39.
State Law of constant proportions. Explain with an example.
Q 40.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 41.
Fill in the blanks:
_________ are building block of all matter.
Q 42.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 43.
How will you define chemical symbol?
Q 44.
Give four examples of diatomic molecules.
Q 45.
Calculate the molecular masses of H
2, O
2, Cl
2, CO
2, CH
4, C
2H
6, C
2H
4, NH
3, CH
3OH.
Q 46.
What are the building blocks of matter ?
Q 47.
Calculate the molecular mass of ethanoic acid, CH
Q 48.
How many atoms are present in one gram atomic mass of a substance ?
Q 49.
(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 50.
Give an example to show Law of conservation of mass applies to physical change also.
