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19 June, 21:55

If a 45 mM phosphate solution (solution A) had an absorbance of 1.012. What would be the absorbance if 11 mL of solution A was used to prepare a 20.0 mL of a new phosphate solution. Write answer to three significant figures.

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  1. 20 June, 01:39
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    0.550

    Explanation:

    The absorbance (A) of a substance depends on its concentration (c) according to Beer-Lambert law.

    A = ε. l. c

    where,

    ε: absorptivity of the species

    l: optical path length

    A 45 mM phosphate solution (solution A) had an absorbance of 1.012.

    A = ε. l. c

    1.012 = ε. l. 45 mM

    ε. l = 0.022 mM⁻¹

    We can find the concentration of the second solution using the dilution rule.

    C₁. V₁ = C₂. V₂

    45mM. 11mL = C₂. 20.0 mL

    C₂ = 25 mM

    The absorbance of the second solution is:

    A = (ε. l). c

    A = (0.022 mM⁻¹). 25 mM = 0.55 (rounding off to 3 significant figures = 0.550)
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