A certain liquid has a normal boiling point of and a boiling point elevation constant . A solution is prepared by dissolving some urea () in

Question

A certain liquid has a normal boiling point of and a boiling point elevation constant . A solution is prepared by dissolving some urea () in of . This solution boils at . Calculate the mass of that was dissolved. Round your answer to significant digits.

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Lệ Thu 5 years 2021-07-14T03:44:49+00:00 1 Answers 48 views 0

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  1. giabao
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    2021-07-14T03:46:36+00:00
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    This question is incomplete, the complete question is;

    A certain liquid X has a normal boiling point of 150.4 °C and a molar boiling point elevation constant kb is 0.60 °Ckgmol⁻¹.

    A solution is prepared by dissolving some urea (NH22CO) in 750 g of X. This solution boils at 150.9 °C . Calculate the mass of urea that was dissolved. Round your answer to 3 significant digits.

    Answer:

    the mass of urea that was dissolved is 37.5 g

    Explanation:

    Given the data in the question;

    normal boiling point of X; Tb⁰ = 150.4 °C

    boiling point of solution Tb = 150.9 °C

    Change in boiling point Δt = Tb – Tb⁰  = 150.9 °C – 150.4 °C = 0.5 °C

    Kb = 0.6 °C.kg.mol⁻¹

    V = 750 g

    Now, we know that

    Δt = Kb × molality

    so

    0.5 = 0.6 × molality

    molality = 0.5 / 0.6

    molality = 0.833

    we know that molar mass of urea is 60 g/mol

    so

    molality = mass × 1000 / molar mass × volume( g )

    we substitute

    0.833 = ( mass × 1000 ) / ( 60 × 750 )

    0.833 = ( mass × 1000 ) / 45000

    0.833 × 45000 = mass × 1000

    mass = ( 0.833 × 45000 ) / 1000

    mass = 37485 / 1000

    mass = 37.485 ≈ 37.5 g   { 3 significance figure }

    Therefore, the mass of urea that was dissolved is 37.5 g

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