5 mL of a lemon soft drink was pipette into a 25 mL volumetr

5 mL of a lemon soft drink was pipette into a 25 mL volumetric flask and diluted to the mark with distilled water. 8 mL of this diluted solution was pipette into a test tube, then 2 mL of distilled water was pipette into the same test tube. Analysis by spectrometry found that the concentration of yellow dye in the test tube solution was 4.7 x 10-5 M. Calculate the concentration of yellow dye in the original soft drink.

Solution

Answer:

Calculation of dilutions:

(1) 5 mL is made upto a volume of 25 mL by making up the volume with 20 mL of water.

So, dilution = 5/25 = 0.2

(2) 8 mL of this solution is made upto a volume of 10 mL by addition of 2 mL of water.

The dilution now = (8/10) * 0.2 = 0.16

Therefore, 4.7 * 10^-5 M is 0.16 times the concentration of the original stock.

So, 0.16 (16%) corresponds to 4.7 * 10^-5 M

1 (100%) corresponds to 4.7 * 10^-5 M / 0.16

= (47/16) * 10^-4 = 2.9375 * 10-4M