Some Basic Concepts Of Chemistry

Question 1

Significant figures
¡) Decimal no. =
¡¡) Non-Decimal no. =

Answer 1

¡) First non zero se sari digits
¡¡) First non zero to last non zero

Question 2

¡) 0.0025
¡¡) 208
¡¡¡)5005
¡v)126000
v) 500.0
v¡)2.0034

Answer 2

¡)2
¡¡)3
¡¡¡)4
¡v)
v)4
v¡)5

Question 3

Molecular mass

Answer 3

> It is the sum of atomic masses of all element resent in a compound.

Question 4

Molecular mass

Answer 4

> It is the sum of atomic masses of all element resent in a compound.

Question 5

Molecular mass of H2O

Answer 5

2(H=1)
2×1=2
O=16
2+16= 18u

Question 6

1. CO
2. CO2
3. HNO3
4. C6H1206

Answer 6

1. 28u
2. 44u
3. 63u
4. 180u

Question 7

Molar mass

Answer 7

It is molecular mass in grams.

Question 8

Molar mass of H20

Answer 8

18g

Question 9

Representation of an element

Answer 9

Atomic mass
ELEMENT
Atomic number

Question 10

Isotopes

Answer 10

Atomic number same
Atomic mass different

Question 11

Any two examples of isotopes

Answer 11

1^1H, 2^1H, 3^1H
12^6C, 14^6C
35^17Cl, 37^17Cl

Question 12

Isobars

Answer 12

Atomic mass same
Atomic number different

Question 13

Any two example of isobars

Answer 13

40^18Ar, 40^20Ca
59^27Co, 59^28Ni

Question 14

Average atomic mass

Answer 14

Relative abundance=R
Atomic mass=A
Avg atomic mass= R1×A1÷100+ R2×A2÷100

Question 15

Find atomic mass
Isotope>Relative abundance>Atomic mass(amu)
^12C>98.892>12
^13C>1.108>13.00335
^14C>2×10^-10>14.00317

Answer 15

Avg atomic= 98.892×12÷100 + 1.108×13.00335÷100 + 2×10^-10×14.00317÷100
=12.001u
(Bas carbon ka atomic number likhkr .smth daldo)

Question 16

Scientific notations
<– =
–> =

Answer 16

+ve
-ve

Question 17

1. 43126
2. 0.000129
3. 0.009625×10^3
   (Pehla digit 10 se kam 9-1)

Answer 17

1. 4.3×10^4
2. 1.29×10^-4
3. 9.6×10^-6

Question 18

Mole concept
Q> Define 1 mole

Answer 18

It is defined as the mass exactly equal to one-twelfth of the mass of one carbon-12 atom

Question 19

No. Of moles?
(Using given mass and molar mass)

Answer 19

No. Of moles,n= Given mass/molar mass

Question 20

No. Of moles?
(Using given number of atoms/molecules/particles?)

Answer 20

No. Of moles,n= Given no of atomes/molecules/particles ÷ 6.022×10^23

Question 21

No. Of moles?
(Using given volume of gas)

Answer 21

No of moles,n= given vol of gas at STP÷ 22.7L

Question 22

Find number of moles present in 16g O2

Answer 22

16g÷32g= 0.5

Question 23

Find number of moles present in 12.044×10^23 atoms of sulphur.

Answer 23

12.044×10^23÷6.022×10^23= 2

Question 24

Find number of moles present in 12.044×10^23 atoms of sulphur.

Answer 24

12.044×10^23÷6.022×10^23= 2

Question 25

Find number of atoms present in 10g S8 molecule

Answer 25

Given mass= 16g
Molar mass= 32×8= 256g
Given mass/molar mass ×no. Of atoms/6.022×10^23
16÷32=x÷6.022×10^23
×=0.37×10^23

Question 26

Empirical formula

Answer 26

It represents the simple whole number ratio of various atoms present in a compound.

Question 27

C2H4
C3H6
C6H12O6

Answer 27

CH2
CH2
CH2O

Question 28

Molecular formula

Answer 28

It shows the exact number of different types of atoms present in a molecule of the compound.

Question 29

A compound contains 92.3% of carbon and remaining hydrogen. If the molar mass is 78g. Find emperical formula and molecular formula. (Pb1.2, ex1.2)

Answer 29

Emperical formula= CH
Emperical mass= 12+1=13
N= molar mass÷emperical mass= 78÷13=6
Molecular formula= (CH)6= C6H6