An unknown amount of a compound with a molecular mass of 273.14 g/mol is dissolv

Question

An unknown amount of a compound with a molecular mass of 273.14 g/mol is dissolved in a 10-mL volumetric flask. A 1.00-mL aliquot of this solution is transferred to a 25-mL volumetric flask and enough water is added to dilute to the mark. The absorbance of this diluted solution at 335 nm is 0.435 in a 1.000 cm cuvette. The molar absorptivity for this compound at 335 nm is es3s 6543 M cm (a) What is the concentration of the compound in the cuvette? Number (b) What is the concentration of the compound in the 10-mL flask? Number How many milligrams of compound were used to make the 10-mL solution? Number mg

Explanation / Answer

(a) concentration = absorbance/molar absorptivity x path length

with,

absorbance = 0.435

molar absorptivity = 6543 M-1.cm-1

path length = 1 cm

we get,

concentration of compound in cuvetter = 0.435/6543 x 1 = 6.65 x 10^-5 M

(b) concentration of compound in 10 ml solution = 6.65 x 10^-5 M x 25/1 = 1.66 x 10^-3 M

(c) mg of compound in 10 ml solution = 1.66 x 10^-3 mol/L x 0.010 L x 273.14 g/mol x 1000

                                                            = 4.534 mg

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