Shelby is measuring chloride concentration in environmental using a chloride on

Question

Shelby is measuring chloride concentration in environmental using a chloride on selective electrode. In order to color the electrode a set of five chloride standards in the 10^-1 to 10^-5 M range is needed. Shelby has a standard solution of 1,000 M NaCl to use in procuring the standards. The glassware available in the lab includes an ample supply of all the volumetric flasks and pipettes displayed in Q1. Shelby pipets 10 mL of the 1,000 M NaCl solution into the 100 mL volumetric flask to volume and mines the solution by inverting the flask 30 times What is the concentration of the resulting solution? What volume of the 1,000 M NaCl solution is required to make 100 mL of the 10.5 M chloride solution? Calculate the volume required for the three remaining concentrations. (Enter each volume secreted by a comma.) What practical difficulties might Shelby encountered when preparing the solution in part b and what could she do to minimize error in making these solutions ?Essay answers are limited to about 500 words (3500 characters maximum, including spaces).

Explanation / Answer

Part (A), 10 mL of 1.000 M NaCl is taken into 100 mL volumetric flask and diluted.

V1 = 10 mL, S1 = 1.000 M, V2 = 100 mL

S2 = (V1 x S1)/V2 = (10 x 1.000)/100 = 0.1 M = 10-1 M

Note: 30 times inverted and mixed has nothing to change with concentration, I guess !!

Part (B) To make 10-5 M NaCl 100 mL from 1.000 M stock

Again V1 = x (unknown), S1 = 1.000 M, V2 = 100 mL, S2 = 10-5 M

V1 S1 = V2 S2

x = 100 x 10-5 = 10-3 mL = 0.001 mL = 1 microlitre

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