JEE Chemistry

Question 1

How many moles of magnesium phosphate, Mg3(PO4)2 will contain 0.25 mole of oxygen atoms?

  • 0.02

  • 3.125 × 10–2

  • 1.25 × 10–2

  • 2.5 × 10–2

Solution

B.

3.125 × 10–2

Mg subscript 3 left parenthesis PO subscript 4 right parenthesis subscript 2
apostrophe straight n apostrophe space moles
8 straight n space equals space 0.25
straight n space equals space fraction numerator 0.25 over denominator 8 end fraction
space equals space fraction numerator 25 over denominator 8 space straight x space 100 end fraction space equals space 3.125 space straight x space 10 to the power of negative 2 end exponent
Question 2

According to Bohr’s theory, the angular momentum of an electron in 5th orbit is

  • 25h/ π

  • 1.0h/π

  • 10/π

  • 2.5h/π

Solution

D.

2.5h/π

m v r space equals fraction numerator 5 straight h over denominator 2 straight pi end fraction space
equals space 2.5 straight h over straight pi
Question 3

Which of the following molecules/ions does not contain unpaired electrons?

  • straight O subscript 2 superscript 2 minus end superscript
  • straight B subscript 2
  • straight N subscript 2 superscript plus
  • straight O subscript 2

Solution

A.

straight O subscript 2 superscript 2 minus end superscript
Question 4

Uncertainty in the position of an electron (mass = 9.1 × 10–31 kg) moving with a velocity 300 ms–1, accurate upto 0.001%, will be

  • 19.2 × 10–2 m

  • 5.76 × 10–2 m

  • 1.92 × 10–2 m

  • 3.84 × 10–2 m

Solution

C.

1.92 × 10–2 m

increment straight x. increment straight v space greater or equal than space fraction numerator straight h over denominator 4 πm end fraction
increment straight x space greater or equal than space fraction numerator straight h over denominator 4 πm increment straight V end fraction space equals space fraction numerator 6.63 space straight x space 10 to the power of negative 34 end exponent over denominator 4 space straight x space 3.14 space straight x space 9.1 space straight x space 10 to the power of negative 31 end exponent space straight x space 300 space straight x space begin display style fraction numerator 0.001 over denominator 100 end fraction end style end fraction
space equals space fraction numerator 6.63 space straight x space 10 to the power of negative 34 end exponent over denominator 4 space straight x space 3.14 space straight x space 9.1 space straight x space 3 space straight x space 10 to the power of negative 31 end exponent space straight x space 10 to the power of negative 3 end exponent end fraction
space equals space 0.01933
space equals space 1.93 space straight x space 10 to the power of negative 2 end exponent
Question 5

Phosphorus pentachloride dissociates as follows, in a closed reaction vessel,
PCl5 (g) ⇌ PCl3(g) + cl2(g)
If total pressure at equilibrium of the reaction mixture is P and degree of dissociation of PCl5 is x, the partial pressure of PCl3 will be

  • open parentheses fraction numerator straight x over denominator straight x plus 1 end fraction close parentheses straight P
  • open parentheses fraction numerator 2 straight x over denominator straight x plus 1 end fraction close parentheses straight P
  • open parentheses fraction numerator straight x over denominator straight x minus 1 end fraction close parentheses straight P
  • open parentheses fraction numerator 2 straight x over denominator straight x minus 1 end fraction close parentheses straight P

Solution

A.

open parentheses fraction numerator straight x over denominator straight x plus 1 end fraction close parentheses straight P PCl subscript 5 space rightwards harpoon over leftwards harpoon with space space space space space space on top space PCl subscript 3 space left parenthesis straight g right parenthesis space plus space space Cl subscript 2 space left parenthesis straight g right parenthesis
left parenthesis 1 minus straight x right parenthesis space space space space space space space space straight x space space space space space space space space space space space space space space space straight x
straight P subscript PCl subscript 3 end subscript space equals open parentheses fraction numerator straight x over denominator 1 plus straight x end fraction close parentheses space straight x space straight P