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14 February, 15:45

Heating 1.124 g of an unknown NaHCO3-NaCl mixture resulted in a mass loss of 0.270 g.

a. Calculate the mass of NaHCO3 present in the original mixture.

b. Calculate the mass percent of NaHCO3 in the unknown mixture to the nearest

percent.

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  1. 14 February, 15:55
    0
    a) 0.731 grams

    b) 65.0 %

    Explanation:

    Step 1: Data given

    Mass of unknown NaHCO3 - NaCl = 1.124 grams

    Mass loss = 0.270 grams

    Molar mass NaHCO3 = 84.00 g/mol

    Step 2: The balanced equation

    2 NaHCO3 → Na2CO3 + H2O + CO2

    Step 3: Calculate moles H2CO3

    All the mass lost was due to an equimolar mixture of H2O and CO2, effectively H2CO3.

    Moles H2CO3 = mass H2CO3 / molar mass H2CO3

    Moles H2CO3 = 0.270 grams / 62.03 g/mol

    Moles H2CO3 = 0.00435 moles

    Step 4: Calculate moles NaHCO3

    For 1 mole H2CO3 produced we need 2 moles NaHCO3

    For 0.00435 moles H2CO3 we need 2*0.00435 = 0.00870 moles NaHCO3

    Step 5: Calculate mass NaHCO3

    Mass NaHCO3 = moles * molar mass

    Mass NaHCO3 = 0.00870 moles * 84.00 g/mol

    Mass NaHCO3 = 0.731 grams

    b. Calculate the mass percent of NaHCO3 in the unknown mixture to the nearest percent.

    mass % = (0.731/1.124) * 100 %

    mass % = 65.0 %
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