Laboratory Experiments 91 QUESTIONS 1. Why is it necessary to use a blank when u

Question

Laboratory Experiments 91 QUESTIONS 1. Why is it necessary to use a blank when using the spectrophotometer? 2. Why do you have to use a volumetrie flask instend of an Erlenmeyer flask or beaker when preparing the solutions in this experiment? 3. If you need to prepare 100.0 mL. of a 0.080 M solution, how much of a 1.6 M stock solution do you need to use? (Show your calculations) If you need to prepare 100.0 ml of a 0.12 M solution, how much of a 0.80 M stock solution do you need to use? (Show your calculations) 4 5 For the dilution equation, Mc Vc Md . Vd, what can be said about the relative values of the concentrations and the relative values of the volumes? Use "less than" or "greater than" in your answers. The value of Ve is alwaysthe value of Vd because The value of Mc is alwaysthe value of Md because Copyright O 2015 Pearson Education, Inc

Explanation / Answer

1)

In order to measure the absorbance of particular substance in reaction mixture, it is required to zero out the spectrophotometer so that the absorbance of only the used substance is measured

2)

Volumetric flask has higher precision than Beaker and Flask, which gives less error rate value of absorbance as compared to the readings done with beaker

3)

Let the volume of stock solution be V

Since number of moles will remain same after dilution, hence we can write

Mc * Vc = Md * Vd

1.6 * Vc = 0.080 * 100

Vc = 5 mL

4)

Let the volume of stock solution be V

Since number of moles will remain same after dilution, hence we can write

Mc * Vc = Md * Vd

0.80 * Vc = 0.12 * 100

Vc = 15 mL

5)

The value of Vc is always less than the volume of Vd, since the volume of concentrated solution is always less than volume of diluted solution

The value of Vc is always less than Vd

The value of Mc is always greater than Md, since on dilution the concentration will decrease

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