Page 1
JEE Main Previous Year Qs (2025):
Some Basic Concepts of Chemistry
Q1: 20 mL of 2 M NaOH solution is added to 400 mL of 0.5 M NaOH solution. The final
concentration of the solution is
____ × 10
-2
M. (Nearest integer)
JEE Main 2025 (Online) 22nd January Evening Shift
Ans: 57
Solution:
To determine the final concentration of the NaOH solution, we use the formula for mixing
solutions :
?? ?? =
?? 1
× ?? 1
+ ?? 2
× ?? 2
?? 1
+ ?? 2
Where :
?? 1
= 2M and ?? 1
= 20 mL : Concentration and volume of the first solution.
?? 2
= 0.5M and ?? 2
= 400 mL : Concentration and volume of the second solution.
Substitute the values into the equation:
?? ?? =
2 × 20 + 0.5 × 400
420
Calculating each term:
2 × 20 = 40
0.5 × 400 = 200
Add these results:
?? ?? =
40 + 200
420
=
240
420
˜ 0.571M
Convert this to scientific notation as the problem specifies the answer should be in × 10
-2
form:
?? ?? = 57.1 × 10
-2
M
Rounded to the nearest integer, the final concentration is:
Q2: During " S " estimation, 160 mg of an organic compound gives 466 mg of barium
sulphate. The percentage of Sulphur in the given compound is ____ %.
(Given molar mass in ?? ?????? -?? of ???? : ?????? , ?? : ???? , ?? : ???? )
JEE Main 2025 (Online) 23rd January Morning Shift
Ans: 40
Solution:
Page 2
JEE Main Previous Year Qs (2025):
Some Basic Concepts of Chemistry
Q1: 20 mL of 2 M NaOH solution is added to 400 mL of 0.5 M NaOH solution. The final
concentration of the solution is
____ × 10
-2
M. (Nearest integer)
JEE Main 2025 (Online) 22nd January Evening Shift
Ans: 57
Solution:
To determine the final concentration of the NaOH solution, we use the formula for mixing
solutions :
?? ?? =
?? 1
× ?? 1
+ ?? 2
× ?? 2
?? 1
+ ?? 2
Where :
?? 1
= 2M and ?? 1
= 20 mL : Concentration and volume of the first solution.
?? 2
= 0.5M and ?? 2
= 400 mL : Concentration and volume of the second solution.
Substitute the values into the equation:
?? ?? =
2 × 20 + 0.5 × 400
420
Calculating each term:
2 × 20 = 40
0.5 × 400 = 200
Add these results:
?? ?? =
40 + 200
420
=
240
420
˜ 0.571M
Convert this to scientific notation as the problem specifies the answer should be in × 10
-2
form:
?? ?? = 57.1 × 10
-2
M
Rounded to the nearest integer, the final concentration is:
Q2: During " S " estimation, 160 mg of an organic compound gives 466 mg of barium
sulphate. The percentage of Sulphur in the given compound is ____ %.
(Given molar mass in ?? ?????? -?? of ???? : ?????? , ?? : ???? , ?? : ???? )
JEE Main 2025 (Online) 23rd January Morning Shift
Ans: 40
Solution:
Millimoles of BaSO
4
=
466
233
= 2mmol
% S =
466
233
× 32
160
× 100 = 40%
Q3 : When 81.0 g of aluminium is allowed to react with 128.0 g of oxygen gas, the
mass of aluminium oxide produced in grams is ____ .
(Nearest integer)
Given :
Molar mass of Al is 27.0 g mol
-1
Molar mass of ?? is 16.0 g mol
-1
JEE Main 2025 (Online) 23rd January Evening Shift
Ans: 153
Solution:
To determine the mass of aluminum oxide produced, we first consider the chemical reaction
between aluminum and oxygen:
4Al + 3O
2
? 2Al
2
O
3
Given:
Molar mass of Al = 27.0 g/mol
Molar mass of O = 16.0 g/mol
81.0 g of Al and 128.0 g of O
2
Calculating moles of reactants:
For aluminum (Al), using its molar mass:
81 g
27 g/mol
= 3 moles of Al
For oxygen ( O
2
), using its molar mass ( O
2
is composed of two oxygen atoms):
128 g
32 g/mol
= 4 moles of O
2
Identifying the limiting reagent:
From the stoichiometry of the reaction:
4 moles of Al react with 3 moles of O
2
3 moles of Al require
3
4
× 3 moles of O
2
= 2.25 moles of O
2
Since only 2.25 moles of O
2
are needed by 3 moles of Al , and we have 4 moles of O
2
, aluminum
is the limiting reagent.
Calculating moles of Al
2
O
3
formed:
Page 3
JEE Main Previous Year Qs (2025):
Some Basic Concepts of Chemistry
Q1: 20 mL of 2 M NaOH solution is added to 400 mL of 0.5 M NaOH solution. The final
concentration of the solution is
____ × 10
-2
M. (Nearest integer)
JEE Main 2025 (Online) 22nd January Evening Shift
Ans: 57
Solution:
To determine the final concentration of the NaOH solution, we use the formula for mixing
solutions :
?? ?? =
?? 1
× ?? 1
+ ?? 2
× ?? 2
?? 1
+ ?? 2
Where :
?? 1
= 2M and ?? 1
= 20 mL : Concentration and volume of the first solution.
?? 2
= 0.5M and ?? 2
= 400 mL : Concentration and volume of the second solution.
Substitute the values into the equation:
?? ?? =
2 × 20 + 0.5 × 400
420
Calculating each term:
2 × 20 = 40
0.5 × 400 = 200
Add these results:
?? ?? =
40 + 200
420
=
240
420
˜ 0.571M
Convert this to scientific notation as the problem specifies the answer should be in × 10
-2
form:
?? ?? = 57.1 × 10
-2
M
Rounded to the nearest integer, the final concentration is:
Q2: During " S " estimation, 160 mg of an organic compound gives 466 mg of barium
sulphate. The percentage of Sulphur in the given compound is ____ %.
(Given molar mass in ?? ?????? -?? of ???? : ?????? , ?? : ???? , ?? : ???? )
JEE Main 2025 (Online) 23rd January Morning Shift
Ans: 40
Solution:
Millimoles of BaSO
4
=
466
233
= 2mmol
% S =
466
233
× 32
160
× 100 = 40%
Q3 : When 81.0 g of aluminium is allowed to react with 128.0 g of oxygen gas, the
mass of aluminium oxide produced in grams is ____ .
(Nearest integer)
Given :
Molar mass of Al is 27.0 g mol
-1
Molar mass of ?? is 16.0 g mol
-1
JEE Main 2025 (Online) 23rd January Evening Shift
Ans: 153
Solution:
To determine the mass of aluminum oxide produced, we first consider the chemical reaction
between aluminum and oxygen:
4Al + 3O
2
? 2Al
2
O
3
Given:
Molar mass of Al = 27.0 g/mol
Molar mass of O = 16.0 g/mol
81.0 g of Al and 128.0 g of O
2
Calculating moles of reactants:
For aluminum (Al), using its molar mass:
81 g
27 g/mol
= 3 moles of Al
For oxygen ( O
2
), using its molar mass ( O
2
is composed of two oxygen atoms):
128 g
32 g/mol
= 4 moles of O
2
Identifying the limiting reagent:
From the stoichiometry of the reaction:
4 moles of Al react with 3 moles of O
2
3 moles of Al require
3
4
× 3 moles of O
2
= 2.25 moles of O
2
Since only 2.25 moles of O
2
are needed by 3 moles of Al , and we have 4 moles of O
2
, aluminum
is the limiting reagent.
Calculating moles of Al
2
O
3
formed:
From the reaction, 4 moles of Al yield 2 moles of Al
2
O
3
. Thus:
3
4
× 2 =
3
2
moles of Al
2
O
3
Calculating mass of Al
2
O
3
:
The molar mass of Al
2
O
3
is:
(2 × 27) + (3 × 16) = 102 g/mol
So, the mass of
3
2
moles of Al
2
O
3
is:
3
2
× 102 = 153 grams
Thus, the mass of aluminum oxide produced is 153 grams.
Q4: 0.01 mole of an organic compound (?? ) containing ???? % hydrogen, on complete
combustion produced ?? . ?? ???? ?? ?? . Molar mass of (?? ) is ____ ?? ?????? -?? .
JEE Main 2025 (Online) 23rd January Evening Shift
Ans: 100
Solution:
Organic compound ?
combustion
H
2
O
0.9gm
? mole of H
2
O =
0.9
18
= 0.05 mole
? mole of H in H
2
O = 0.05 × 2 = 0.1 mole
= mole of H in 0.01 mole
Organic compound
? wt of H atom in 0.01 mole compound = 0.1 × 1
= 0.1gm
? wt of H atom in one mole compound
=
0.1
0.01
= 10gm
? wt. % of ?? =
wt. of ?? in one mole compound
Molar mass of compound
× 1
10 =
10
?? × 100
? ?? = 100
Q5: Xg of benzoic acid on reaction with aq ?????????? ?? released ????
?? that occupied
???? . ???? volume at STP. X is ____ g.
JEE Main 2025 (Online) 24th January Morning Shift
Page 4
JEE Main Previous Year Qs (2025):
Some Basic Concepts of Chemistry
Q1: 20 mL of 2 M NaOH solution is added to 400 mL of 0.5 M NaOH solution. The final
concentration of the solution is
____ × 10
-2
M. (Nearest integer)
JEE Main 2025 (Online) 22nd January Evening Shift
Ans: 57
Solution:
To determine the final concentration of the NaOH solution, we use the formula for mixing
solutions :
?? ?? =
?? 1
× ?? 1
+ ?? 2
× ?? 2
?? 1
+ ?? 2
Where :
?? 1
= 2M and ?? 1
= 20 mL : Concentration and volume of the first solution.
?? 2
= 0.5M and ?? 2
= 400 mL : Concentration and volume of the second solution.
Substitute the values into the equation:
?? ?? =
2 × 20 + 0.5 × 400
420
Calculating each term:
2 × 20 = 40
0.5 × 400 = 200
Add these results:
?? ?? =
40 + 200
420
=
240
420
˜ 0.571M
Convert this to scientific notation as the problem specifies the answer should be in × 10
-2
form:
?? ?? = 57.1 × 10
-2
M
Rounded to the nearest integer, the final concentration is:
Q2: During " S " estimation, 160 mg of an organic compound gives 466 mg of barium
sulphate. The percentage of Sulphur in the given compound is ____ %.
(Given molar mass in ?? ?????? -?? of ???? : ?????? , ?? : ???? , ?? : ???? )
JEE Main 2025 (Online) 23rd January Morning Shift
Ans: 40
Solution:
Millimoles of BaSO
4
=
466
233
= 2mmol
% S =
466
233
× 32
160
× 100 = 40%
Q3 : When 81.0 g of aluminium is allowed to react with 128.0 g of oxygen gas, the
mass of aluminium oxide produced in grams is ____ .
(Nearest integer)
Given :
Molar mass of Al is 27.0 g mol
-1
Molar mass of ?? is 16.0 g mol
-1
JEE Main 2025 (Online) 23rd January Evening Shift
Ans: 153
Solution:
To determine the mass of aluminum oxide produced, we first consider the chemical reaction
between aluminum and oxygen:
4Al + 3O
2
? 2Al
2
O
3
Given:
Molar mass of Al = 27.0 g/mol
Molar mass of O = 16.0 g/mol
81.0 g of Al and 128.0 g of O
2
Calculating moles of reactants:
For aluminum (Al), using its molar mass:
81 g
27 g/mol
= 3 moles of Al
For oxygen ( O
2
), using its molar mass ( O
2
is composed of two oxygen atoms):
128 g
32 g/mol
= 4 moles of O
2
Identifying the limiting reagent:
From the stoichiometry of the reaction:
4 moles of Al react with 3 moles of O
2
3 moles of Al require
3
4
× 3 moles of O
2
= 2.25 moles of O
2
Since only 2.25 moles of O
2
are needed by 3 moles of Al , and we have 4 moles of O
2
, aluminum
is the limiting reagent.
Calculating moles of Al
2
O
3
formed:
From the reaction, 4 moles of Al yield 2 moles of Al
2
O
3
. Thus:
3
4
× 2 =
3
2
moles of Al
2
O
3
Calculating mass of Al
2
O
3
:
The molar mass of Al
2
O
3
is:
(2 × 27) + (3 × 16) = 102 g/mol
So, the mass of
3
2
moles of Al
2
O
3
is:
3
2
× 102 = 153 grams
Thus, the mass of aluminum oxide produced is 153 grams.
Q4: 0.01 mole of an organic compound (?? ) containing ???? % hydrogen, on complete
combustion produced ?? . ?? ???? ?? ?? . Molar mass of (?? ) is ____ ?? ?????? -?? .
JEE Main 2025 (Online) 23rd January Evening Shift
Ans: 100
Solution:
Organic compound ?
combustion
H
2
O
0.9gm
? mole of H
2
O =
0.9
18
= 0.05 mole
? mole of H in H
2
O = 0.05 × 2 = 0.1 mole
= mole of H in 0.01 mole
Organic compound
? wt of H atom in 0.01 mole compound = 0.1 × 1
= 0.1gm
? wt of H atom in one mole compound
=
0.1
0.01
= 10gm
? wt. % of ?? =
wt. of ?? in one mole compound
Molar mass of compound
× 1
10 =
10
?? × 100
? ?? = 100
Q5: Xg of benzoic acid on reaction with aq ?????????? ?? released ????
?? that occupied
???? . ???? volume at STP. X is ____ g.
JEE Main 2025 (Online) 24th January Morning Shift
Ans: 61
Solution:
C
6
H
5
COOH+ NaHCO
3
? C
6
H
5
COONa
+
+H
2
O + CO
2
× ???? 11.2 L
mole of C
6
H
5
COOH= mole of CO
2
=
11.2
22.4
= 0.5
mass of C
6
H
5
COOH= x = 0.5 × 122 = 61gm
Q6: Consider the following reaction occurring in the blast furnace:
????
?? ?? ?? ( ?? )
+ ?? ????
(?? )
? ?? ????
(?? )
+ ?? ????
?? ( ?? )
'
??
'
???? of iron is produced when ?? . ???? ×
????
?? ???????? ?? ?? ?? and ?? . ?? × ????
?? ???????? are brought together in the furnace. The value of '
?? ' is . (nearest integer) {Given:molar mass of ????
?? ?? ?? = ?????? ?? ?????? -?? , molar mass of
???? = ???? ?? ?????? -?? , molar mass of ???? = ???? ?? ?????? -?? }
JEE Main 2025 (Online) 24th January Morning Shift
Ans: 420
Solution:
moles of Fe
3
O
4
=
2.32×10
3
×10
3
232
= 10000 mol
moles of CO =
2.8×10
2
×10
3
28
= 10000 mol
Fe
3
O
4
+ 4CO? 3Fe + 4CO
2
10
4
mol 10
4
mol
CO is L.R.
mole of Fe =
3
4
× 10
4
mass of Fe =
3
4
×
10
4
×56
1000
kg = 420 kg
Q7: Quantitative analysis of an organic compound (X) shows following % composition.
C : ???? . ?? %
Cl : 64.46%
?? : ?? . ?? %
(Empirical formula mass of the compound (?? ) is ____ × ????
-??
(Given molar mass in ?? ?????? -?? of ?? : ???? , ?? : ?? , ?? : ???? , ???? : ???? . ?? )
JEE Main 2025 (Online) 28th January Morning Shift
Page 5
JEE Main Previous Year Qs (2025):
Some Basic Concepts of Chemistry
Q1: 20 mL of 2 M NaOH solution is added to 400 mL of 0.5 M NaOH solution. The final
concentration of the solution is
____ × 10
-2
M. (Nearest integer)
JEE Main 2025 (Online) 22nd January Evening Shift
Ans: 57
Solution:
To determine the final concentration of the NaOH solution, we use the formula for mixing
solutions :
?? ?? =
?? 1
× ?? 1
+ ?? 2
× ?? 2
?? 1
+ ?? 2
Where :
?? 1
= 2M and ?? 1
= 20 mL : Concentration and volume of the first solution.
?? 2
= 0.5M and ?? 2
= 400 mL : Concentration and volume of the second solution.
Substitute the values into the equation:
?? ?? =
2 × 20 + 0.5 × 400
420
Calculating each term:
2 × 20 = 40
0.5 × 400 = 200
Add these results:
?? ?? =
40 + 200
420
=
240
420
˜ 0.571M
Convert this to scientific notation as the problem specifies the answer should be in × 10
-2
form:
?? ?? = 57.1 × 10
-2
M
Rounded to the nearest integer, the final concentration is:
Q2: During " S " estimation, 160 mg of an organic compound gives 466 mg of barium
sulphate. The percentage of Sulphur in the given compound is ____ %.
(Given molar mass in ?? ?????? -?? of ???? : ?????? , ?? : ???? , ?? : ???? )
JEE Main 2025 (Online) 23rd January Morning Shift
Ans: 40
Solution:
Millimoles of BaSO
4
=
466
233
= 2mmol
% S =
466
233
× 32
160
× 100 = 40%
Q3 : When 81.0 g of aluminium is allowed to react with 128.0 g of oxygen gas, the
mass of aluminium oxide produced in grams is ____ .
(Nearest integer)
Given :
Molar mass of Al is 27.0 g mol
-1
Molar mass of ?? is 16.0 g mol
-1
JEE Main 2025 (Online) 23rd January Evening Shift
Ans: 153
Solution:
To determine the mass of aluminum oxide produced, we first consider the chemical reaction
between aluminum and oxygen:
4Al + 3O
2
? 2Al
2
O
3
Given:
Molar mass of Al = 27.0 g/mol
Molar mass of O = 16.0 g/mol
81.0 g of Al and 128.0 g of O
2
Calculating moles of reactants:
For aluminum (Al), using its molar mass:
81 g
27 g/mol
= 3 moles of Al
For oxygen ( O
2
), using its molar mass ( O
2
is composed of two oxygen atoms):
128 g
32 g/mol
= 4 moles of O
2
Identifying the limiting reagent:
From the stoichiometry of the reaction:
4 moles of Al react with 3 moles of O
2
3 moles of Al require
3
4
× 3 moles of O
2
= 2.25 moles of O
2
Since only 2.25 moles of O
2
are needed by 3 moles of Al , and we have 4 moles of O
2
, aluminum
is the limiting reagent.
Calculating moles of Al
2
O
3
formed:
From the reaction, 4 moles of Al yield 2 moles of Al
2
O
3
. Thus:
3
4
× 2 =
3
2
moles of Al
2
O
3
Calculating mass of Al
2
O
3
:
The molar mass of Al
2
O
3
is:
(2 × 27) + (3 × 16) = 102 g/mol
So, the mass of
3
2
moles of Al
2
O
3
is:
3
2
× 102 = 153 grams
Thus, the mass of aluminum oxide produced is 153 grams.
Q4: 0.01 mole of an organic compound (?? ) containing ???? % hydrogen, on complete
combustion produced ?? . ?? ???? ?? ?? . Molar mass of (?? ) is ____ ?? ?????? -?? .
JEE Main 2025 (Online) 23rd January Evening Shift
Ans: 100
Solution:
Organic compound ?
combustion
H
2
O
0.9gm
? mole of H
2
O =
0.9
18
= 0.05 mole
? mole of H in H
2
O = 0.05 × 2 = 0.1 mole
= mole of H in 0.01 mole
Organic compound
? wt of H atom in 0.01 mole compound = 0.1 × 1
= 0.1gm
? wt of H atom in one mole compound
=
0.1
0.01
= 10gm
? wt. % of ?? =
wt. of ?? in one mole compound
Molar mass of compound
× 1
10 =
10
?? × 100
? ?? = 100
Q5: Xg of benzoic acid on reaction with aq ?????????? ?? released ????
?? that occupied
???? . ???? volume at STP. X is ____ g.
JEE Main 2025 (Online) 24th January Morning Shift
Ans: 61
Solution:
C
6
H
5
COOH+ NaHCO
3
? C
6
H
5
COONa
+
+H
2
O + CO
2
× ???? 11.2 L
mole of C
6
H
5
COOH= mole of CO
2
=
11.2
22.4
= 0.5
mass of C
6
H
5
COOH= x = 0.5 × 122 = 61gm
Q6: Consider the following reaction occurring in the blast furnace:
????
?? ?? ?? ( ?? )
+ ?? ????
(?? )
? ?? ????
(?? )
+ ?? ????
?? ( ?? )
'
??
'
???? of iron is produced when ?? . ???? ×
????
?? ???????? ?? ?? ?? and ?? . ?? × ????
?? ???????? are brought together in the furnace. The value of '
?? ' is . (nearest integer) {Given:molar mass of ????
?? ?? ?? = ?????? ?? ?????? -?? , molar mass of
???? = ???? ?? ?????? -?? , molar mass of ???? = ???? ?? ?????? -?? }
JEE Main 2025 (Online) 24th January Morning Shift
Ans: 420
Solution:
moles of Fe
3
O
4
=
2.32×10
3
×10
3
232
= 10000 mol
moles of CO =
2.8×10
2
×10
3
28
= 10000 mol
Fe
3
O
4
+ 4CO? 3Fe + 4CO
2
10
4
mol 10
4
mol
CO is L.R.
mole of Fe =
3
4
× 10
4
mass of Fe =
3
4
×
10
4
×56
1000
kg = 420 kg
Q7: Quantitative analysis of an organic compound (X) shows following % composition.
C : ???? . ?? %
Cl : 64.46%
?? : ?? . ?? %
(Empirical formula mass of the compound (?? ) is ____ × ????
-??
(Given molar mass in ?? ?????? -?? of ?? : ???? , ?? : ?? , ?? : ???? , ???? : ???? . ?? )
JEE Main 2025 (Online) 28th January Morning Shift
Ans: 1655
Solution:
Identify the given weight percentages from a 100 g sample:
Carbon (C): 14.5 g
Chlorine (Cl): 64.46 g
Hydrogen (H): 1.8 g
Since the sample must sum to 100 g , the remaining mass is from oxygen (O) :
O: 100 - (14.5 + 64.46 + 1.8) = 100 - 80.76 = 19.24 g.
Next, convert these masses to moles using the given atomic masses:
Moles of C:
14.5 g
12 g/ mol
˜ 1.2083 mol .
Moles of Cl :
64.46 g
35.5 g/mol
˜ 1.8171 mol .
Moles of H :
1.8 g
1 g/mol
= 1.8 mol .
Moles of O :
19.24 g
16 g/mol
˜ 1.2025 mol .
Now, find the simplest whole-number ratio by dividing each by the smallest number of moles
(approximately 1.2025 mol ):
Ratio for C:
1.2083 /1.2025 ˜ 1.00
Ratio for O:
1.2025 /1.2025 = 1.00
Ratio for H:
1.8/1.2025 ˜ 1.50
Ratio for Cl:
1.8171 /1.2025 ˜ 1.51 ˜ 1.50
Since the ratios for H and Cl are about 1.5, multiplying all ratios by 2 will give whole numbers:
C: 1 × 2 = 2
O: 1 × 2 = 2
H: 1.5 × 2 = 3
Cl : 1.5 × 2 = 3
Thus, the empirical formula of the compound is:
C
2
H
3
O
2
Cl
3
.
Calculate the empirical formula mass by summing the contributions:
C: 2 × 12 = 24 g/mo l
H: 3 × 1 = 3 g/mol
O: 2 × 16 = 32 g/mol
Cl : 3 × 35.5 = 106.5 g/mol
Total mass:
24 + 3 + 32 + 106.5 = 165.5 g/mol .
The problem asks for the empirical formula mass in the form " × 10
-1
". We can express
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