TEST YOURSELF 1.7 Chemistry 9th Chapter 1

TEST YOURSELF 1.7

(1)How many atoms of Sodium are present in 3 moles of Sodium and what is the mass of it ?

Given data :

No of moles of sodium = 3 mol

No of sodium atoms = ?

Mass of sodium = ?

Solution :

No of sodium atoms = No of moles * N_A

No of sodium atoms = 3 * 6.02 * 10²³

                                      = 18.06 * 10²³ atoms

Mass of sodium = ?

Mass of sodium = No of moles * Molar mass

Mass of sodium =?

Mass of sodium = No of moles * Molar mass

                            = 3*23

                            = 69 grams

(2) How many atoms are in 1 amu and 1 g of hydrogen (H)?

Given Data :

Mass of Hydrogen = 1 amu

Mass of Hydrogen = 1 g

No. of Hydrogen atoms in both =?

Solution:

1 amu = 1.66* 10^-24 g

Number of hydrogen atoms =Mass of hydrogen atoms/Molar mass * N_A

                                                 = 1.66*10^-24/1 * 6.02*10²³

                                                 = 0.999 atoms

                                                 = 9.99*10^-1

                                                 = 1 atom

No. of hydrogen atoms in 1 gram=Mass of hydrogen/Molar mass*N_A

No. of atoms of Hydrogen in 1 g = 1/1 *6.02*10²³

                                                         = 6.02*10²³ atoms

(3) How many atoms are present in 16 g of O and 8 g of S?

Given Data :

Mass of O = 16 gram

Mass of S = 8 gram

No of atoms of both?

Solution :

No. of O atoms = Mass of O / Molar mass of O * N_A

No. of O atoms = 16/ 16 * 6.02*10²³

                           = 6.02*10²³ atoms

No. of Sulphur atoms = Mass of S / Molar mass of S * N_A

No. of S atoms = 8/ 32 * 6.02 *10²³

                          = 1.5 * 10²³ atoms

(4) Is the mass of 1 mole of O and 1 mole of S same?

1 atom of carbon means there is only 1 carbon atom. While 1 gram atom of carbon means the atomic mass of carbon expressed in grams which is 12g.

(5)  If 16 g of oxygen contains 1 mole of oxygen atoms calculate the mass of one atom of oxygen in grams.

1 mole of O atoms = 16 grams

Also, 1 mole of O atoms =  6.02*10²³ atoms of O

6.02*10²³ atoms of O has mass = 16 grams

1 atom of O has mass = 16 / 6.02*10²³ * 1

                                        = 2.65*10^-23 grams

(7) How many times is 1 mole of oxygen atom heavier than 1 mole of hydrogen atom?

1 mole of oxygen atom = 16 grams

1 mole of hydrogen atom = 1 gram

The ratio between these two will be 1:16

It means that 1 mole of oxygen atom is 16 times heavier than 1 mole of hydrogen atom.

(8) Why does 10 g nitrogen gas contain the same number of molecules as 10 g of carbon monoxide?

Mass of N₂ = 10 grams                            Mass of CO = 10 grams

Molar mass of N₂ = 28 g mol^-1                Molar mass of CO = 28 g mol^-1

No. of N₂ molecules =?                            No. of CO molecules = ?

No. of molecules of N₂                                             No. molecules of CO

= Mass of N₂/Molar mass*6.02*10²³     = Mass of CO/ Molar mass *N_A

= 10/28*6.02*10²³                                       = 10/ 28 *6.02*10²³

= 2.15*10²³  molecules                              = 2.15*10²³  molecules 

10 g nitrogen gas contain the same number of molecules as 10 g of  carbon monoxide because both have the same molar mass i.e. 28 g mol^-1

TEST YOURSELF 1.6 Chemistry 9th Chapter 1

TEST YOURSELF 1.6

(1)            Which term is used to represent the mass of 1 mole of molecules of a substance?

Gram molecular mass is used to represent the mass of 1 mole of molecules of a substance.

(2)            How many atoms are present in one gram atomic mass of a substance?

6.02*10²³ atoms are present in one gram atomic mass of a substance. Because one gram means that atomic mass of a substance expressed in grams.

(3)            Explain the relationship between mass and mole of a substance.

The relationship between mass and mole of a substance is given as following :

Mass of a substance = No of moles * Molar mass

(4)            Find out the mass of 3 moles of oxygen atoms?

No of moles of oxygen = 3 mol

               Molar mass of oxygen atom = 16 g mol^-1

               Mass of oxygen atom = No of moles * Molar mass

               Mass of oxygen atom = 3*16

                                       = 48 grams

(5)             How many molecules of water are present in half mole of water?

      No of moles of water = ½ mol

      Number of water molecules = ?

      Number of water molecules = No of moles * N_A

      Number of water molecules = ½ * 6.02*10²³

                                                          =3.01 * 10²³ molecules

TEST YOURSELF 1.5 Chemistry 9th chapter 1

TEST YOURSELF 1.5

(1)               Identify the following as diatomic, triatomic or polyatomic molecules.

Sr.No	Diatomic	Triatomic	Polyatomic
1	H2	H2O	H2SO4
2	HCl	CO2	C6H6
3	CO	-	-

(2)               Identify the following as cation, anion, free radical, molecular ion or molecule :

Sr.No	Cation	Anion	Free radical	Molecular ion	Molecule
1	Na+	H-	Br-	CO32-	N2
2	-	O2-	-	N2+	O2
3	-	-	-	-	Cl2

TEST YOURSEF 1.4 Chemistry 9th Chapter 1

TEST YOURSEF 1.4

(1) What is the relationship between empirical formula and formula unit?

The empirical formula shows the simplest ratio of atoms in covalent compounds. While the formula unit shows the simplest whole number ratio of ions as present in the ionic compound. Since both tell us the simplest units of compounds and simplest ratio. So, they are equal and same for covalent as well as ionic compounds.

 

(2) How can you differentiate between molecular formula and empirical formula?

     

Sr.No	Molecular Formula	Empirical Formula
1	Molecular formula shows the actual number of atoms of each element in a molecule of that compound.	Empirical formula shows the simplest whole number ratio of atoms present in a compound.
2	Example:C6H6(Benzene) ,C6H12O6(Glucose) etc	Example:CH(Benzene) ,CH2O(Glucose)etc.

Remember :

                     Some compounds may have same empirical formula and molecular formula e.g. H₂O, HCl etc.

(3) Identify the following formulae as formula units or molecular formula?

Sr.No	Molecular Formula	Empirical Formula
1	H2O2, C6H12O6	BaCO3

            CH₄ and C₁₂H₂₂O₁₁ have same empirical and molecular formula.

(4)   What is empirical formula of acetic acid (CH₃COOH)? Find out its molecular mass.

The acetic acid is actually C₂H₄O₂. The empirical formula of acetic acid is CH₂O.

Molecular mass :

CH₃COOH = (2*23)+(1*32)+(4*16)

=24+32+64

= 60 amu

(5)     Calculate the formula masses of :

          Na₂SO₄, ZnSO₄ and CuCO₃

Na₂CO₃ = (2*23) + ( 1*32) + (4*16)

                                                = 46+32+64

                                                = 142 amu

ZnSO₄ = (1*65) + (1*32) + (4*16)

                                               = 65+32+64

                                               = 161 amu

CuCO₃ = (1*63.5) + (1*12) + (3*16)

                                              = 63.5+12+48

                                              = 123.5 amu 

TEST YOURSELF 1.3 Chemistry 9th Chapter 1

TEST YOURSELF 1.3

(1)  How many amu 1 g of a substance has ?

1.66*10^-24 gram   =  1 amu

1 gram   = 1/1.66*10^-24

1 gram  = 6.0 * 10 ^-24  amu

(2)  Is atomic mass unit a SI unit of an atomic mass?

No, atomic mass unit is not a SI unit of an atomic mass.

(3)  What is the relationship between atomic number and atomic mass?

The relationship between atomic number and atomic mass is given   as following:

A = Z+n

A = Atomic mass

Z = Atomic number

n = Number of neutrons

(4)  Define relative atomic mass.

“The relative atomic mass of the atoms of an element as compared to 1/12^th the mass of an atom of carbon-12 isotope.The unit for relative atomic mass is called amu and is equal to :

1       amu = 1.66 * 10^-24 gram.

(5)  Why atomic mass of an atom I defined as relative atomic mass?

The mass of an atom of an element is too small to be determined practically. We have certain instruments which enable us to determine the ratio of the atomic masses of various elements to that of carbon-12. This ratio is called relative atomic mass of the element. Therefore, atomic mass of an atom is defined as relative atomic mass.

TEST YOURSELF 1.2 Chemistry 9th Chapter 1

                       

                        TEST YOURSELF 1.2

(1)  Can you identify mixture, elements and compounds out of the followings:

Sr.No	Elements	Compounds	Mixture
1	Aluminium	Sugar	Coca Cola, Ice cream
2	Silicon	Table Salt	Petroleum, Urine
3	Tin	Lime	Blood, Gun powder

(2)    Air is homogenous mixture. Justify. Identify substances present in it.

  Air is homogenous mixture because it has throughout uniform composition. It has no formula. It is a mixture of nitrogen, hydrogen , oxygen and noble gases like Argon (Ar) etc.

(3)     Name the elements represented by following symbols:

  

Sr. No	Symbols	Elements	Symbols	Elements
1	Hg	Mercury	Au	Gold
2	Fe	Iron	Ni	Nickle
3	Co	Cobalt	W	Tungsten
4	Sn	Tin	Na	Sodium
5	Ba	Barium	Br	Bromine
6	Bi	Bismuth	B	Boron

(4)     Name a solid , liquid and a gaseous  element that exist at the room temperature.

Solid elements= Aluminium , Iron ,Gold etc.

Liquid elements= Mercury, Bromine

Gaseous elements= Oxygen, Nitrogen, Hydrogen etc.

(5)    Which element do the following compounds contain?

Sr.No	Compound	Formula	Elements
1	Sugar	C12H22O11	Carbon, Hydrogen and oxygen.
2	Common Salt	NaCl	Sodium and chlorine
3	Lime Water	Ca(OH)2	Calcium, oxygen and Hydrogen.
4	Chalk	CaCO3	Calcium, Carbon and Oxygen.