Using an analytical balance that has a sensitivity of 03mg a

Using an analytical balance that has a sensitivity of 0.3mg and any of the volumetric flasks in the table blow, design a procedure to prepare at least 50 mL of a 1.5x10-2M solution of sodium chloride with a precision of +/-0.5%. Assume the sodium chloride is pure and dry.

Describe what and why you chose your specific sample weight and volumetric flask. Be sure to also include the range of weights of NaCl that will give an acceptable concentration for the volumetric flask you are using. If your final solution is more than 50 mL, explain why.

Solution

0.003/x = 0.005 x= 0.6 So we must use at least this much NaCl to be within tolerance. The MW of NaCl is 58.44 g/mole. Let\'s start with the 100 mL v-flask. MW H2O = 18.053 g/mol. So, 100 mL = 100/18.053 = 5.54 moles. 5.54 x 1.5 x 10^-2 = 0.083 moles needed of NaCL. 58.44 *0.083 =4.850 g. This is way more than we need to stay within tolerance by itself. The maximum error would be .003/4.850 + .08/100 = 0.0014 or 0.14% We are well withing tolerance. Let\'s see if that would work for 50 mL flask. .004/2.425 + 0.04/50 = 0.002 Also within tolerance. So, we can use the smaller flask

Procedure: Place about 20 mL of H2O in 50 mL volumetric flask. Weigh out 2.425 grams of NaCl add to 20 mL of NaCl and add to flask. Fill to line.

range of NaCl is +- 0.005 of NaCl target weight so (2.425*0.995) - (2.425*1.005) = 2.413 - 2.437 g