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Solutions question

2011 · Q91
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Solutions question

2011 · Q91

NEETChemistrySolutionsMCQ+4 / −1
The freezing point depression constant for water is −-−1.86o C m−-−1. If 5.00 g Na2SO4 is dissolved in 45.0 g H2O, the freezing point is changed by −-−3.82oC. Calculate the van't Hoff factor for Na2SO4.
  1. A
    2.05
  2. B
    2.63
  3. C
    3.11
  4. D
    0.381
View written solutionFree

Correct answer: B

According to depression in freezing point,

Δ\Delta ΔTf = i ×\times× Kf ×\times× m

= i ×\times× Kf ×\times× wB×1000mB×wA{{{w_B} \times 1000} \over {{m_B} \times {w_A}}}mB​×wA​wB​×1000​

Given : Δ\Delta ΔTf = 3.82, Kf = 1.86,

wB = 5, mB = 142, wA = 45

i = ΔT×mB×wAKf×wB×1000{{\Delta T \times {m_B} \times {w_A}} \over {{K_f} \times {w_B} \times 1000}}Kf​×wB​×1000ΔT×mB​×wA​​

= 3.82×142×451.86×5×1000{{3.82 \times 142 \times 45} \over {1.86 \times 5 \times 1000}}1.86×5×10003.82×142×45​

= 2.63

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