PLOT #1 Scatter Plot with a trend-line: A scatter plot will be used in this course when one variable that is controlled effects another variable. The variable being purposefully manipulated is called the independent variable and is plotted on the horizontal axis. In this case our independent variable is concentration. The measured or dependent variable is plotted on the vertical axis. Absorbance is our dependent variable and is a quantity you will learn about in this course. It is measured with a spectrophotometer which shines a single wavelength of light on a sample and measures how much light the sample absorbs. You will be adding a “trend-line” to your data set which is the straight line that passes closest to all of the points as possible (called the line of best fit.) This line can be used to predict the relationship between these 2 variables even in between the points that were generated in the experiment! For example, you can read the absorbance of an unknown sample and predict its concentration.
Using these instructions, create a graph of the above data set that has the following features: 1. Format the axis so the x starts at 55, and the y starts at 0.5. Add additional tick marks to both of the axes. (Excel will automatically select the bounds on the axes so that your data fills the graph – which can be problematic when trying to compare two graphs. This is why setting the axis scale manually is often best practice.) 2. Label the axes: y=”Absorbance” and x= “Concentration in g/L” (Style guides for most scientific journals recommend using sentence case for axis titles. The recommended titles should reflect this and have the first letter capitalized.) 3. Add the title “Effect of concentration of compound A on absorbance at 650nm, (your name)” 4. Add a linear trend-line and display the equation and R-squared value on the graph NOTE: The on-line instructions describe a “+” icon next to the chart. If you do not have a “+” icon, select the “chart design” tab at the top and the “add chart element” button in the upper left to add something to the chart. Select the “Format” tab at the top and click on the various elements in the chart. You will see the pane on the right change when you click the data, trend-line, axes etc. which will allow you to make the desired modifications. Also, for Mac users, one can right-click by holding down the “control” key and clicking.