Your lab instructor asks you to prepare a series of five standard solutions to be used to make a...
Question:
Your lab instructor asks you to prepare a series of five standard solutions to be used to make a Beer's Law plot for copper sulfate which is blue-colored. The first solution should be 1/2 the concentration of the stock solution which is 0.1 M CuSO4 and each solution should have a total volume of at least 50 mLs. Explain precisely how you would prepare the standard solutions including volumes, glassware, etc.
Making Standard Solutions
Standard solutions are used in order to make a Beer-Lambert plot. This law states that there should be a linear relationship between the concentration of an analyte and its absorbance. This law is usually analysed via UV-Vis spectroscopy. In order to ensure a good relationship, the standard solutions need to be accurately made.
Answer and Explanation: 1
The equation we need in order to calculate how much volume we need of the copper sulphate stock solution, in order to make standard solutions for Beer-Lambert analysis, is {eq}C_1V_1=C_2V_2 {/eq}.
{eq}C_1 {/eq} is the concentration of copper sulphate stock solution, {eq}V_1 {/eq} is the volume of copper sulphate stock solution taken, {eq}C_2 {/eq} is the concentration of the standard solutions we are making, and {eq}V_2 {/eq} is the volume of the standard solutions. We already know {eq}C_1 {/eq} (0.1 M), {eq}C_2 {/eq}, and {eq}V_2 {/eq} (50 mL). {eq}C_2 {/eq} is decided amongst ourselves and it is easier to take nice increments of concentration i.e. 0.01 M, making sure we start with 0.05 M as this is half the concentration of the stock solution. Therefore, we need to rearrange the equation to make {eq}V_1 {/eq} the subject, which is {eq}V_1={C_2V_2}/{C_1} {/eq}. Now we can use the equation and we should get the answers below.
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So using a measuring cylinder we should measure the volumes needed of the stock solution, making sure the bottom of the meniscus is on the line of the volume that is needed. This then should be added to a 50 mL volumetric flask and filled to the line, shown on the flask at 50 mL, with the same solvent used in the stock solution. The lowest part of the meniscus should be on this line in order to get an accurate concentration. It is useful to use a glass pipette and add the solvent in drop-wise when near this line, in order to make sure we don't go over. Finally, a stopper needs to be placed on top of the flask and shaken in order to ensure the solvent and stock solution are mixed well together.
Learn more about this topic:
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Chapter 8 / Lesson 11Learn about standard solutions in chemistry. Understand the definition of standard solutions, what standard solution is used for, and explore how to prepare standard solutions.