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17 August, 16:49

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

CaF2 + H2SO4 - -> CaSO4 + 2HF

The chemist uses 11 g of CaF2 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 (2)
  1. 17 August, 17:27
    0
    A. The theoretical yield of HF is 5.64g

    B. The percentage yield of HF is 39%

    Explanation:

    Step 1:

    The balanced equation for the reaction:

    CaF2 + H2SO4 - -> CaSO4 + 2HF

    Step 2:

    Determination of the mass of CaF2 that reacted and the mass of HF produced from the balanced equation. This is illustrated below:

    Molar Mass of CaF2 = 40 + (19x2) = 40 + 38 = 78g/mol

    Molar Mass of HF = 1 + 19 = 20g/mol

    Mass of HF from the balanced equation = 2 x 20 = 40g.

    From the balanced equation above,

    78g of CaF2 reacted and 40g of HF were produced.

    A. Determination of the theoretical yield of HF.

    This is illustrated below:

    From the balanced equation above,

    78g of CaF2 reacted to produce 40g of HF.

    Therefore, 11g of CaF2 will react to produce = (11 x 40) / 78 = 5.64g of HF.

    The theoretical yield of HF is 5.64g

    B. Determination of the percentage yield.

    The percentage yield of HF can be obtained as follow:

    Actual yield = 2.2g

    Theoretical yield = 5.64g

    Percentage yield = ?

    Percentage yield = Actual yield/Theoretical yield x100

    Percentage yield = 2.2/5.64 x 100

    Percentage yield = 39%

    The percentage yield of HF is 39%
  2. 17 August, 18:07
    0
    39.3%

    Explanation:

    Our guide in solving the problem must be the reaction equation hence it is pertinent to put down first:

    CaF2 + H2SO4 - -> CaSO4 + 2HF

    We have a very important information in the question, sulphuric acid is present in excess. This implies that calcium fluoride is the limiting reactant.

    Number of moles of calcium fluoride reacted = mass of calcium fluoride reacted / molar mass of calcium fluoride

    Molar mass of calcium fluoride = 78.07 g/mol

    Number of moles of calcium fluoride = 11g/78.07 g/mol = 0.14 moles of Calcium flouride

    Since 1 mole of calcium fluoride yields two moles of 2 moles hydrogen fluoride

    0.14 moles of calcium fluoride will yield 0.14*2 = 0.28 moles of hydrogen fluoride

    Mass of 0.28 moles of hydrogen fluoride = number of moles * molar mass

    Molar mass of hydrogen flouride = 20.01 g/mol

    Mass of HF = 0.28 moles * 20.01 g/mol = 5.6 g this is the theoretical yield of HF

    Actual yield of HF was given in the question as 2.2g

    % yield of HF = actual yield / theoretical yield * 100

    %yield of HF = 2.2/5.6 * 100

    % yield of HF = 39.3%
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