A compound with a molecular mass of 287.29 was dissolved in a 5 mL volumetric fl

Question

A compound with a molecular mass of 287.29 was dissolved in a 5 mL volumetric flask. A 1.00 mL aliquot was withdrawn, placed in a 10 mL volumetric flask, and diluted to the mark. The absorbance at 340 nm was 0.427 in a 1.000 cm cuvet. The molar absorptivity for this compound at 340 nm is = 6130 M-1 cm-1. (a) Calculate the concentration of compound in the cuvet. (answer in M) (b) What was the concentration of compound in the 5 mL flask? (answer in M) (c) How many milligrams of compound were used to make the 5 mL solution? (answer in M) (Please show HOW you got the answers too)

Explanation / Answer

Best Answer - Chosen by Voters (a) A=ebc c=A/eb c=.427/ (6130 x 1) c= 6.97e-5M (b) not all of the 5.00 mls of stock was diluted , only 1.00 ml of the stock solution was diluted up to 10 ml c1v1=c2v2 c1(1.00mL)=(6.966e-5)(10.00ml) your answer is: c1=6.97e-4 M is the strength of the one ml taken from the 5ml stock, & the strength of all of the mls in the 5ml stock as well which changes the next 6.966e-4mol/L x 287.29 g/mol x 1000mg/g =495ppm Answer : 495 ppm c) you have the 6.966e-4Molarity & 5 ml's... we could calculate the moles,: 0.005 litres @ 6.966e-4 mol/litre = 3.483e-6 moles then use the molar mass to calculate the grams used" 3.483e-6 moles @ 287.29 g/mol = 1.0026e-3 grams Answer: 1.0026e-3 grams Thank you..

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