Read the following:

- T & P 1 – Weighing, Bottle-Top Dispenser, and Graphing
- Demonstrations of Nine Practical Lab Techniques – Techniques 4 and 5

We will be working on Techniques 4 and 5. Read through the lab carefully before coming to the lab.

Read the following:

- T & P 1 – Weighing, Bottle-Top Dispenser, and Graphing
- Demonstrations of Nine Practical Lab Techniques – Techniques 4 and 5

We will be working on Techniques 4 and 5. Read through the lab carefully before coming to the lab.

When using Excel to generate this graph, be sure to pay attention to the following points:

- When adding the trendline, right-mouse click over a data point. From the context menu, select:
*Linear*as the Trend/Regression Type*Set intercept 0,0**Display line on chart**Display R-squared value on chart*

- For this graph, the slope of the trendline needs to display 3 significant figures in order to get 3 significant figures for the sample’s unknown concentration. Right-mouse click over the equation of the trend line. From the context menu, select
*Format Trendline label*.

- Select
*Number*on the left menu. In the Category menu, select*Number*. In the Decimal Places field, type ‘4’. Click*Close*.

When you prepare your computer-generated graph for next week, do NOT use the Physics software “Graph it”.

“Graph it” is a macro for Excel. You should learn to generate the graph from inputting the data in Excel.

Start by inputting the data points into Excel, select the points and click *Insert > Scatter* (see image below).

That’s how you start! Go to the other posts to refine your graph so that it will include everything that’s needed. Also refer to your hand-plotted graph for this exercise.

Have fun!

Many important relationships can be expressed by graphing. For the analysis of materials, a *standard* curve is used to determine the concentration of a substance (i.e. – the unknown sample).

The analyst first prepares samples of the substance in various known concentrations (i.e. – the standards). The method of preparation should be similar to the unknown that is being measured. The analyst subjects the standards, one at a time, to an analytical instrument and records the data pair (Sample Concentration, Instrument Response) for each standard.

The following is data collected for a set of standards. **A sample of some unknown concentration gives an instrument response of 0.78 mV.**

First, plot a standard curve using the following data. A graph of the instrument response is plotted on the Y-axis and the concentration on the X-axis. The known variable is always plotted on the X-axis and the measured variable is always plotted on the Y-axis. Use the standard curve to determine the unknown concentration of the sample.

Sample Concentration (g/mL) | Instrument Response (mV) |

0.0 | 0.00 |

10.0 | 0.14 |

20.0 | 0.28 |

30.0 | 0.41 |

40.0 | 0.52 |

50.0 | 0.71 |

65.0 | 0.84 |

75.0 | 1.04 |

80.0 | 1.15 |

How to generate an acceptable graph to determine the concentration of the unknown sample.

- Use the whole sheet.
- Label the axes. (Note: the axes have units.)
- Write the title of the graph. (Note: “Y versus X”)
- Draw the best straight line through the points. Force the line through the origin, (0,0). (Note: Do not connect the dots.)
- Determine the equation of the line. (Note: For hand-drawn graphs, pick two points that the line goes through. These points may or may not be the data points. For computer-generated graphs, add the trendline and the R
^{2}value.)

Write the equation of the line on the graph. - For computer-generated graphs, need to add minor tick or grid marks on both axes.
- Write the slope of the line on the graph. (Note: slope has units.)
- Use the equation of the best fit line to calculate the unknown concentration of the sample.
- Label the unknown sample point on the graph. Draw a line from this point to the y-axis. Draw a line from this point to the x-axis. These lines MUST be perpendicular to the axes.
- Write the concentration of the unknown sample on the graph.

Let your instructor sign your hand-drawn graph before you leave. Graph the same set of data using Excel. Print a copy of the graph and let a classmate do a written peer review on the graph. Discuss the peer review together. Fix your graph in Excel. Reprint the fixed graph and hand in BOTH Excel-generated graphs (classmate critiqued graph and the corrected graph) next week.

Next week, this is what you hand in:

- A cover page that clearly indicates your name and the peer reviewer(s)’ names.
- Print and label your original graph : GRAPH 1.
- Print GRAPH 1 for each peer reviewer to review your graph. Reviewer must use a different colour pen to write comments on the graph to make your comments stand out. Call this graph “Graph 2″.
- An Excel-generated graph with the corrections. Call this graph “Graph 3″.

**Introduction:**

**Review:**