Question:
What is meant by the term chemical formula?
Answer:
A chemical formula is a representation of chemical compound using a set of chemical symbols that forms the compound. It may be an empirical formula or a molecular formula. The molecular formula represents the actual number of atoms of elements present in the compound. While empirical formula tells the whole number ratio of atoms of elements present in the compound.
e.g. The empirical formula of Water is HO which tells it consists of hydrogen and oxygen atoms. The chemical (molecular) formula of Water is : H2O, which tells 2 Hydrogen atoms combine with one atom of oxygen.
The chemical formula of a molecular compound is determined by the valency of each element.
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.
If one mole of nitrogen molecules weighs 28 g, calculate mass of one molecule of nitrogen in grams.
Q 5.
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 6.
What name is given to the number 6.022 x 10
Q 7.
How many moles are 3.6 g of water ?
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.
What is the mass of 0.2 mole of oxygen atoms ?
Q 13.
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 14.
Is there any exception to law of conservation of mass?
Q 15.
Fill in the blanks:
The _______________ of a compound is a symbolic representation of its composition.
Q 16.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 17.
How many moles are there in 4.6 gms of Sodium(Na)?
Q 18.
What is meant by atomicity ? Explain with two
Q 19.
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 20.
How many moles are there in 34.5 g of sodium ? (Atomic mass of Na = 23 u)
Q 21.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 22.
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 23.
Calculate the molecular mass of chloroform (CHC1
Q 24.
Calculate the number of molecules in 4 g of oxygen.
Q 25.
Calculate the mass in grams of 0.17 mole of hydrogen sulphide, H
Q 26.
(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 27.
(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 28.
State Law of constant proportions. Explain with an example.
Q 29.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 30.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 31.
Fill in the blanks:
Hydrogen and oxygen combines to form H
2O and H
2O
2. These two compounds obey the law of ____________________.
Q 32.
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 33.
Work out the formulae for the following compounds :
(a) Sodium oxide
Q 34.
Name the following compounds. Also write the symbols/formulae of the ions present in them :
(a) CuSO
Q 35.
What are the postulates of Dalton's atomic theory?
Q 36.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 37.
Give four examples of diatomic molecules.
Q 38.
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 39.
Calculate the molecular masses of the following :
(a) Hydrogen, H
Q 40.
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 41.
Name the elements water is made of. What are the valencies of these elements ? Work out the chemical formula for water.
Q 42.
Find the mass of 2 moles of nitrogen atoms.
Q 43.
Give an example to show Law of conservation of mass applies to physical change also.
Q 44.
Fill in the blanks:
_________ are building block of all matter.
Q 45.
What is the atomic mass unit?
Q 46.
What are polyatomic ions? Give examples?
Q 47.
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 48.
What are the building blocks of matter ?
Q 49.
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Q 50.
Calculate the molecular masses of the following compounds :
(a) Methane, CH
