Chemistry

Atoms and Molecules

Question:

Write the chemical formulae of the following. Also identify the ions present.
(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate
(d) Aluminium chloride
(e) Calcium carbonate.

Answer:


(a) Magnesium chloride: MgCl2 (ions present are: Mg2+, Cl1- )
(b) Calcium oxide: CaO (ions present are: Ca2+, O2- )
(c) Copper nitrate: Cu(NO3)2 (ions present are: Cu2+, NO31- )
(d) Aluminium chloride: AlCl3 (ions present are: Al3+, Cl1- )
(e) Calcium carbonate: CaCO3 (ions present are: Ca2+, CO32- )
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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.

An element Z has a valency of 3. What is the formula of oxide of Z ?

Q 3.

What is the numerical value of Avogadro number ?

Q 4.

Write the full form of IUPAC.

Q 5.

If one mole of nitrogen molecules weighs 28 g, calculate mass of one molecule of nitrogen in grams.

Q 6.

How many moles are there in 4.6 gms of Sodium(Na)?

Q 7.

How many moles of calcium carbonate (CaCO3) are are present in 10 g of the substance ? (Ca = 40 u • C= 12 u-O = 16 u)

Q 8.

What is meant by atomicity ? Explain with two

Q 9.

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 10.

Is there any exception to law of conservation of mass?

Q 11.

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 12.

What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.

Q 13.

What name is given to the number 6.022 x 1023

Q 14.

How many moles are 3.6 g of water ?

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.

Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.

Q 19.

The molecular formula of glucose is C6H12O6. Calculate its molecular mass. (Atomic masses : C = 12 u ; H =1 u ; O = 16 u)

Q 20.

Calculate the number of molecules in 4 g of oxygen.

Q 21.

Show by means of calculations that 5 moles of CO, and 5 moles of H2O do not have the same mass. How much is the difference in their masses ?

Q 22.

Explain with example that law of conservation of mass is valid for chemical reactions.

Q 23.

State Law of constant proportions. Explain with an example.

Q 24.

What is relative atomic mass of an element? How it is related to atomic mass unit?

Q 25.

Calculate the molecular mass of chloroform (CHC13).
(Atomic masses :C= 12u;H = lu;Cl = 35.5u)

Q 26.

How many moles are there in 34.5 g of sodium ? (Atomic mass of Na = 23 u)

Q 27.

If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.

Q 28.

(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 29.

(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)Al2O3(ii) co2(iii) C12O7 (iv) H2SO4(p)A12(S04)3

Q 30.

Fill in the blanks:
Atoms can be observed using ____________ Microscope.

Q 31.

Give four examples of diatomic molecules.

Q 32.

Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.

Q 33.

Calculate the molecular mass of ethanoic acid, CH3COOH.
(Atomic masses :C = 12u;H = lu;0 = 16u)

Q 34.

Name the elements water is made of. What are the valencies of these elements ? Work out the chemical formula for water.

Q 35.

Name the following compounds. Also write the symbols/formulae of the ions present in them :
(a) CuSO4
(b) (NH4)2SO4
(c)Na2O
(d)Na2CO3
(e)CaCl2

Q 36.

Calculate the mass in grams of 0.17 mole of hydrogen sulphide, H2S.

Q 37.

Which postulate of Dalton’s atomic theory can explain the law of definite proportions?

Q 38.

What is the molecular mass of a substance?

Q 39.

What are the building blocks of matter ?

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.

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 42.

Work out the formulae for the following compounds :
(a) Sodium oxide

Q 43.

What are the postulates of Dalton's atomic theory?

Q 44.

Name the international organization who approves names of elements.

Q 45.

How will you define chemical symbol?

Q 46.

What is the atomic mass unit?

Q 47.

Fill in the blanks:
Hydrogen and oxygen combines to form H2O and H2O2. These two compounds obey the law of ____________________.

Q 48.

What are polyatomic ions? Give examples?

Q 49.

Write down the names of compounds represented by the following formulae:

(i) Al2(SO4)3
(ii) CaCl2
(iii) K2SO4
(iv) KNO3
(v) CaCO3

Q 50.

Calculate the molecular masses of H2, O2, Cl2, CO2, CH4, C2H6, C2H4, NH3, CH3OH.