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16 June, 03:40

1. A chemist prepares hydrogen fluoride by means of the following reaction:

CaF2 + H2SO4 - > CaSO4 + 2HF

The chemist uses 11 g of CaFz and an excess of H2SO4, and the reaction produces 2.2 g of HF.

(a) Calculate the theoretical yield of HF.

(b) Calculate the percent yield of HF.

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Answers (1)
  1. 16 June, 06:50
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    a) Theoretical Yield of HF = 5.64 grams

    b) Percentage Yield = 39%

    Explanation:

    Reaction Given:

    CaF2 + H2SO4 - > CaSO4 + 2HF

    CaF2 = 11g

    H2SO4 = Used in excess

    HF = 2.2 g production = Actual Yield

    So, Let's write down the molar masses:

    Molar Mass of CaF2 = 78 g / mol

    Molar Mass of HF = 20 g/mol

    From the reaction, we can see the 1 mole of CaF2 gives the 2 moles of HF

    i. e

    a) Theoretical Yield of HF:

    1 mole CaF2 = 2 moles HF

    78 g CaF2 = 2 x 20 g of HF

    78 g CaF2 = 40 g of HF

    1 g CaF2 = 40g/78g of HF

    And in the question it is given that chemist used 11 g of CaF2 so,

    1 x 11 g of CaF2 = 11 x 40/78 g of HF

    11 g of CaF2 = 440/78 g of HF

    11 g of CaF2 = 5.64 g of HF

    And this is the theoretical yield

    Theoretical Yield of HF = 5.64 grams

    b) Now, calculate the Percentage Yield of HF

    Percentage Yield = Actual Yield / Theoretical Yield x 100

    Percentage Yield = 2.2 g / 5.64 g x 100

    Percentage Yield = 39%
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