Mole Concept & Stoichiometry · JEE Main previous year questions

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2020 16 questions

Q522020 · 6 Sept 2020 · Shift 1
A solution of two components containing $n_{1}$ moles of the $1^{st}$ component and $n_{2}$ moles of the $2^{nd}$ component is prepared. $M_{1}$ and $M_{2}$ are the molecular weights of component 1 and 2 respectively. If d is the density of the solution in $g m L^{- 1}$ , $C_{2}$ is the molarity and $x_{2}$ is the mole fraction of the $2^{nd}$ component, then $C_{2}$ can be expressed as :
1. A. $C_{2} = \frac{1000 x _{2}}{M _{1} + x _{2} ( M _{2} - M _{1} )}$
2. B. $C_{2} = \frac{1000 d x _{2}}{M _{1} + x _{2} ( M _{2} - M _{1} )}$
3. C. $C_{2} = \frac{d x _{2}}{M _{1} + x _{2} ( M _{2} - M _{1} )}$
4. D. $C_{2} = \frac{d x _{1}}{M _{1} + x _{2} ( M _{2} - M _{1} )}$
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Answer: B
Q712020 · 6 Sept 2020 · Shift 2· Numerical answer
A solution of phenol in chloroform when treated with aqueous NaOH gives compound P as a major product. The mass percentage of carbon in P is ______. (to the nearest integer) (Atomic mass : C = 12; H = 1; O = 16)
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Answer: 69
Q622020 · 3 Sept 2020 · Shift 1
1. A.
2. B.
3. C.
4. D.
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Answer: D, B
Q522020 · 3 Sept 2020 · Shift 2
The strengths of 5.6 volume hydrogen peroxide (of density 1 g/mL) in terms of mass percentage and molarity (M), respectively, are: (Take molar mass of hydrogen peroxide as 34 g/mol)
1. A.0.85 and 0.5
2. B.0.85 and 0.25
3. C.1.7 and 0.25
4. D.1.7 and 0.5
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Answer: D
Q662020 · 3 Sept 2020 · Shift 2
Complex A has a composition of $H_{12} O_{6} C l_{3} Cr$ . If the complex on treatment with $conc. H_{2} S O_{4}$ loses $13.5%$ of its original mass, the correct molecular formula of A is : [Given: atomic mass of $Cr = 52 amu$ and $Cl = 35 amu$ ]
1. A. $[Cr (H_{2} O)_{5} Cl] C l_{2} \cdot H_{2} O$
2. B. $[Cr (H_{2} O)_{4} C l_{2}] Cl \cdot 2 H_{2} O$
3. C. $[Cr (H_{2} O)_{3} C l_{3}] \cdot 3 H_{2} O$
4. D. $[Cr (H_{2} O)_{6}] C l_{3}$
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Answer: B
Q682020 · 3 Sept 2020 · Shift 2
A mixture of one mole each of $H_{2}$ , $He$ and $O_{2}$ each are enclosed in a cylinder of volume $V$ at temperature $T$ . If the partial pressure of $H_{2}$ is $2 atm$ , the total pressure of the gases in the cylinder is :
1. A. $14 atm$
2. B. $38 atm$
3. C. $6 atm$
4. D. $22 atm$
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Answer: C
Q742020 · 3 Sept 2020 · Shift 2· Numerical answer
$6.023 \times 1 0^{22}$ molecules are present in $10 g$ of a substance 'x'. The molarity of a solution containing $5 g$ of substance 'x' in $2 L$ solution is ____ $\times 1 0^{- 3}$
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Answer: 25
Q632020 · 2 Sept 2020 · Shift 2
Two compounds A and B with same molecular formula ( $C_{3} H_{6} O$ ) undergo Grignard's reaction with methylmagnesium bromide to give products C and D. Products C and D show following chemical tests. | Test | C | D | | :--- | :--- | :--- | | Ceric ammonium nitrate Test | Positive | Positive | | Lucas Test | Turbidity obtained after five minutes | Turbidity obtained immediately | | Iodoform Test | Positive | Negative | C and D respectively are :
1. A. $C = (C H_{3})_{3} C - OH$ ; $D = C H_{3} - C H_{2} - CH (OH) - C H_{3}$
2. B. $C = C H_{3} - C H_{2} - C H_{2} - C H_{2} - OH$ ; $D = (C H_{3})_{3} C - OH$
3. C. $C = C H_{3} - C H_{2} - C H_{2} - C H_{2} - OH$ ; $D = C H_{3} - C H_{2} - CH (OH) - C H_{3}$
4. D. $C = C H_{3} - C H_{2} - CH (OH) - C H_{3}$ ; $D = (C H_{3})_{3} C - OH$
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Answer: D
Q752020 · 2 Sept 2020 · Shift 2· Numerical answer
The ratio of the mass percentages of ‘C & H’ and ‘C & O’ of a saturated acyclic organic compound ‘X’ are 4 : 1 and 3 : 4 respectively. Then, the moles of oxygen gas required for complete combustion of two moles of organic compound ‘X’ is ________.
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Answer: 5
Q712020 · 9 Jan 2020 · Shift 1· Numerical answer
The hardness of a water sample containing $1 0^{- 3} M MgS O_{4}$ expressed as $CaC O_{3}$ equivalents (in ppm) is _______. (molar mass of $MgS O_{4}$ is $120.37 g/mol$ )
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Answer: 100
Q722020 · 9 Jan 2020 · Shift 1· Numerical answer
The molarity of $HN O_{3}$ in a sample which has density 1.4 g/mL and mass percentage of 63% is _______. (Molecular Weight of $HN O_{3} = 63$ )
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Answer: 14
Q512020 · 9 Jan 2020 · Shift 2
The first and second ionisation enthalpies of a metal are 496 and $4560 kJ mol^{- 1}$ , respectively. How many moles of $HCl$ and $H_{2} S O_{4}$ , respectively, will be needed to react completely with 1 mole of the metal hydroxide ?
1. A.1 and 2
2. B.1 and 0.5
3. C.1 and 1
4. D.2 and 0.5
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Answer: B
Q682020 · 9 Jan 2020 · Shift 2
Biochemical Oxygen Demand (BOD) is the amount of oxygen required (in ppm) :
1. A.for sustaining life in a water body.
2. B.by anaerobic bacteria to breakdown inorganic waste present in a water body.
3. C.for the photochemical breakdown of waste present in $1 m^{3}$ volume of a water body.
4. D.by bacteria to break-down organic waste in a certain volume of a water sample.
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Answer: D
Q722020 · 9 Jan 2020 · Shift 2· Numerical answer
10.30 mg of $O_{2}$ is dissolved into a liter of sea water of density 1.03 g/mL. The concentration of $O_{2}$ in ppm is_______.
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Answer: 10
Q752020 · 9 Jan 2020 · Shift 2· Numerical answer
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Answer: 66.66 to 66.67
Q602020 · 8 Jan 2020 · Shift 1
1. A. $XY, 2 \times 1 0^{- 6} M^{3}$
2. B. $X Y_{2}, 1 \times 1 0^{- 9} M^{3}$
3. C. $X Y_{2}, 4 \times 1 0^{- 9} M^{3}$
4. D. $X_{2} Y, 2 \times 1 0^{- 9} M^{3}$
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Answer: C