Molarity/Dilutions Lab Practical This lab practical will test your knowledge on

Question

Molarity/Dilutions Lab Practical This lab practical will test your knowledge on molarity & dilution calculations and wil also assess your lab skills of preparing solutions accurately and taking proper absorbance measurements from a spectrophotometer Part A. Molarity Calculations & Solution Preparation Directions: 1. Prepare exactly 50 mL of a 005 M solution of CoCl 6H:0 using the crystalline reagent. (Hint: Don't forget to include the moles of water in your molar mass calculations) Show all work for your calculations and write a detailed explanation on how the solution was accurately prepared including all equipment/glassware utilized as well as the steps that were followed Calculations/Explanation: 2. After your assigned solution is prepared, measure the absorbance on a spectrophotometer at 515 nm. Be sure to use deionized water as the reference/blank. Explain the procedure that you followed for taking the absorbance measurement. Absorbance @ 515nm

Explanation / Answer

This is the calculation for the preparation of CoCl2.6H2O.

Volume = 50 mL = 0.05 L

Molarity = 0.0005 M

Molar mass of CoCl2.6H2O = (58.93 + 2*35.5 + 12*1 + 16*6)

= 237.93 g/mol

We know, Molarity = Weight of solute taken/ (Molecular weight of solute * Volume of solution in litres)

On substituting the values in above equation,

0.0005 = Weight taken / (0.05 * 237.93)

Weight taken = 0.0059 g.

So first you need to accurately weigh 0.0059 g of CoCl2.6H2O. Then take a 50 mL volumetric flask and add 0.0059 g of CoCl2.6H2O to it. Then fill up the volumetric flask with water using a measuring cylinder till the 50 mL mark. Check that the level of water should not cross the mark. For adding the last few drops of water to the flask, use a dropper to be accurate. Now the 50 mL 0.0005M CoCl2.6H2O solution is ready. You will have a pink colored solution.

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