Use the data in the table below to make a standard curve of...

Use the data in the table below to make a standard curve of the concentration versus the absorbance. You may work in small groups. Concentration of the standard solutions (µg/mL) | Absorbance 5.0 µg/mL | 0.1 6.0 µg/mL | 0.2 8.0 µg/mL | 0.4 9.0 µg/mL | 0.5 11.0 µg/mL | 0.7 13.0 µg/mL | 0.9 1. What is the dependent variable of your graph and on which axis is it graphed? 2. What is the independent variable and on which axis is it graphed? 3. What would be the absorbance of a solution with a concentration of 7.0 µg/mL? 4. What is the concentration of a solution with an absorbance of 0.8? 5. Now, suppose you had an unknown sample that had been diluted as follows: 1 mL of unknown + 3 mL of solvent. This diluted sample was then tested and had an absorbance of 0.6. What is the concentration of the original solution? Show all of your work done to determine this. 6. Finally, suppose you had an unknown sample with an absorbance of 2.2. Could you determine its concentration directly from the standard curve? Why or why not?

Transcript

00:02 So you are having a graph that's showing a concentration of a sample and the absorbance value from a spectrophotometer.

00:12 So the very first question, it says that, what is the dependent variable of your graph and on which axis it graphed? in this case, a dependent variable, we call it dv, equals the absorbance value.

00:32 This is because you manipulate or you change the concentration of the sample intentionally and then the absorbance value changes according to the concentration.

00:43 So this is the data you collect.

00:45 So again, dependent variable dv is absorbance value and on which axis is graphed and it must be the y -axis.

00:54 The second question, what is the independent variable and on which axis it is graphed? so independent variable iv is the parameter that you change intentionally.

01:06 So in this case, it's the concentration of the sample.

01:12 So you change the sample concentration intentionally and then you will want to see the effect of the change of the concentration and see how it affects the change of absorbance.

01:25 And x -axis will be the axis that the independent variable will be graphed.

01:32 So remember, absorbance is always y and concentration of the sample is always x.

01:38 The next question, three, what would be the absorbance of the solution with the concentration of the 7 .0 microgram per mil? so for this, you'll first of all have to calculate the concentration or the standard curve between concentration and absorbance.

01:55 Let's go to excel to do this.

02:12 So you can tell that the concentration is already being listed in the first column and absorbance is going to be on a second column.

02:28 So the very first thing you're going to do is select both columns.

02:31 Then you're going to insert and you will choose the scatter chart in the first one.

02:39 So you'll see x and y and we can label the axis and x -axis and y -axis.

02:46 X is going to be the concentration and with a unit of microgram per mil and y -axis is going to be the absorbance.

02:59 Now just make sure you label the x and y -axis properly.

03:04 Each of these dots are the sample.

03:07 You have six samples.

03:08 You have six dots and right click one of the dot and click add trendline and you will see a menu coming out with all the meters they can change.

03:19 It's a linear correlation between concentration absorbance and you check display equation on chart and this is going to be your standard curve.

03:27 Y equals 0 .1 x minus or minus 0 .4.

03:33 So remember this is your curve and then once you get this curve, you're able to calculate either concentration or absorbance according to the other one that we know.

03:45 Now since we have the curve, let's go back into our whiteboard to do the rest.

03:56 So question three.

04:03 So three says that we have obviously copy the curve here first for you to easy to see 0 .1 x minus 0 .4.

04:15 So we know that the absorbance is the y so we want to find out the y and 0 .1 times x in this case is 7 .0 microgram per milliliter.

04:31 So we plug the x in there and then minus 0 .4.

04:35 So y equals 0 .7 minus 0 .4 equals 0 .3.

04:42 So when concentration is 7, the absorbance is 0 .3 according to our standard curve.

04:52 Now number four.

04:54 What is the concentration of a solution with absorbance of 0 .8? so use the same method.

05:01 We plug into the same equation of the standard curve.

05:05 This time the absorbance is going to be plugged into y first and 0 .1 times x minus 0 .4.

05:13 So we know concentration.

05:15 We can calculate absorbance and the other way around.

05:18 If we know the absorbance, we can also calculate for concentration...

Question

Please give Ace some feedback