Lab 3 Introduction

Chesapeake Campus – Chemistry 112 Laboratory

LAB #3 – GRAPHING OF LABORATORY DATA

  • Review the ideal gas law, temperature conversions and other concepts from CHM 111.
  • Find the Enthalpy of Vaporization using the Clausius-Clapeyron equation.
  • Graph given, measured or calculated data values manually.
  • Graph data and find a trendline using Microsoft Excel.IntroductionGraphing Data
    This course is data intensive. It is imperative students learn to properly organize and graph data. The primary purpose of this lab is to give students practice in managing data conversions and graphing both manually and within Microsoft Excel. (This program is free to all TCC students http://web.tcc.edu/academics/elearning/tech_requirements.html). Students may wish to review graphing prior to coming to lab this week. A brief review is included here but may not be sufficient for some students.Manual graphs should always:

    • Be drawn on graph paper.
    • Include data points (and possibly the labels as well).
    • Have labels for the graph itself (named Y vs. X), the axes (with both aname and the units), and (if applicable) the legend.
    • Be drawn large enough to visually see all components.
    • Include axis scales that are appropriate (they may not start at 0, dependingon the data).
    • Contain a line of best-fit.Graphs done in Microsoft Excel should always
    • Include all of the components of manual graphs.
    • Be in the “scatter” chart type unless otherwise specified.
    • Include the equation for the line of best fit.This lab contains three sections designed to give students experience graphing data.Part A: Ideal Gas Law
      Recall the Ideal Gas Law. The Ideal Gas Law relates the properties of a gas (pressure, volume, temperature and mol). The Ideal Gas Law has the formula PV = nRT

Equation 1

Tidewater Community College 2015 CC-BY-SA CHM 112 Lab 3 Dichloromethane data from http://en.wikipedia.org/wiki/Dichloromethane_(data_page) CC-BY-SA 3.0 Page 1

where P is the pressure in atmospheres, V is the volume in liters, n is mol, and T is the temperature in Kelvin. R is a constant that has the value 0.08206 𝐿 𝑎𝑡𝑚. Part A gives the data for a set of

𝑚𝑜𝑙 𝐾

experiments. You are given the volume, temperature, and mass of a gas sample. It is necessary to ensure all the units of the data correspond to the units in the gas constant so that any calculation performed will be to the correct units. For example, if you are given grams of the gas sample, it is possible to convert to mols using molar mass. This ensures the units will be the same as those for amount used in the gas constant.

Part B: Kinetics
Later in this semester we will discuss detailed concepts related to chemical kinetics. One of

the types of experiments we evaluate will be decomposition reactions. In a decomposition reaction, a compound breaks apart into two or more components. In some experiments, it is necessary to evaluate how quickly a compound is decomposing. This can be accomplished by measuring the concentration at different intervals.

If a compound is colored, we can use Beer’s Law to evaluate how quickly the color is disappearing. Consider a solution of Kool-Aid that becomes more and more pale as ice melts into it. It is a similar situation where the color of the solution would slowly become less vibrant as the compound decomposes. As long as a set of standards are used to relate the concentration of the compound to the color (absorbance) of the solution, it is possible to calculate the concentration of samples within a matter of seconds. For example, a graph of Absorbance vs. Concentration could be used to find the trendline of best fit. This trendline would contain the equation relating the concentration to absorbance. See the example below:

0.8 0.6 0.4 0.2

0

Absorbance vs Concentration

y = 1.25x + 0.114

0.2 0.3 0.4 0.5 0.6

Concentration (M)

0 0.1

Here we have a graph with standards of known concentration were created, and the absorbance measured. The resulting trendline Y = 1.25 X + 0.114 relates the absorbance (Y) to the concentration (X). This equation can be used to find the concentration of samples.

Part C: Clausius-Clapeyron Equation
The Clausius-Clapeyron equation is a relationship between the temperature of a liquid sample

and its vapor pressure. Although vapor pressure increases as temperature rises, it is not usually a linear relationship. Therefore the most common form of the equation is given as:

Tidewater Community College 2015 CC-BY-SA CHM 112 Lab 3 Dichloromethane data from http://en.wikipedia.org/wiki/Dichloromethane_(data_page) CC-BY-SA 3.0 Page 2

Absorbance (A)

𝑃 ∆𝐻11 𝐿𝑁1=− (−)

𝑃𝑅𝑇𝑇 212

Equation 2 In this section of the lab, you will be given data for both pressure and temperature values. You

Where the natural log allows for a more linear relationship to be depicted.
will need to convert them to the units indicated above (namely LN(P) and 1. Once you have these

𝑇

values, you can create a graph of LN(P) vs 1.. This graph will have a trendline essentially 𝑇

LN(P) = – ∆𝐻𝑣𝑎𝑝 + C. Since your Y is the Ln(P) and your X is the 1, the slope will have the value 𝑅𝑇 𝑇

– ∆Hvap. Multiplying the value by R will give the heat of vaporization (in joules) at that temperature. R

For this part of the lab, we will be using the R value of 8.3144 𝐽 . 𝐾

Tidewater Community College 2015 CC-BY-SA
Dichloromethane data from http://en.wikipedia.org/wiki/Dichloromethane_(data_page) CC-BY-SA 3.0