Question:
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
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.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 2.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 3.
What is gram-atomic mass of an element?
Q 4.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 5.
Define 'formula mass' of a compound.
Q 6.
What are polyatomic ions? Give examples?
Q 7.
If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Q 8.
What are the postulates of Dalton's atomic theory?
Q 9.
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 10.
Give four examples of diatomic molecules.
Q 11.
What are the building blocks of matter ?
Q 12.
Fill in the blanks:
Atomic radius is measured in __________.
Q 13.
Fill in the blanks:
The mass of 1 mole of a substance is called its _____________.
Q 14.
What is the law of conservation of mass?
Q 15.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 16.
What is the chemical symbol for iron?
Q 17.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 18.
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Q 19.
(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 20.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 21.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 22.
Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide
Q 23.
Define mole. What is its significance?
Q 24.
What is meant by atomicity ? Explain with two
Q 25.
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 26.
How many atoms are there in 0.25 mole of hydrogen ?
Q 27.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 28.
Fill in the blanks:
According to Dalton's atomic theory, atoms of different elements differ in ______, size and chemical properties.
Q 29.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 31.
What are ionic compounds?
Q 32.
Write the full form of IUPAC.
Q 33.
What is meant by the symbol of an element ? Explain with examples.
Q 34.
Calculate the molecular masses of the following compounds :
(a) Methanol, CH
Q 35.
Work out the formula for magnesium hydrogencarbonate.
Q 36.
What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.
Q 37.
How many atoms are present in one gram atomic mass of a substance ?
Q 38.
Calculate the number of molecules in 4 g of oxygen.
Q 39.
(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 40.
(a) What is meant by the 'molar mass'of a substance ? State the unit in which molar mass usually expressed.
(b) Calulate the molar masses of the following substances. Write the results with proper units
(1) Ozone molecule, O
Q 41.
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 42.
Fill in the blanks:
Mass of 2 Hydrogen atoms is __________.
Q 43.
Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Q 45.
What is gram-molecular mass of a substance?
Q 46.
When 'mole' was chosen internationally standard way to express larger number of chemical units?
Q 47.
Calculate the number of molecules of sulphur (S
8) present in 16 g of solid sulphur.
Q 48.
Calculate the molecular mass of nitric acid,HNO
Q 49.
Calculate the molecular mass of hydrogen bromide (HBr).
(Atomic masses: H=1; Br= 80 U)
Q 50.
Write down the formulae for the following compounds :
(a) Calcium oxide
(b) Magnesium hydroxide
