Measuring Your Results

Determine the uncertainty for the gravimetric analysis described in Example 8.1. (a) How does your result compare with the expected accuracy of 0.1-0.2% for precipitation gravimetry (b) What sources of error might account for any discrepancy between the most probable measurement error and the expected accuracy ... 

Your process may produce wastes that cannot be treated on-site, and so must be transported off-site for treatment and disposal. Wastes of this type are usually non-aqueous liquids, sludge, or solids. Often, wastes for off-site disposal are costly to transport and to treat, and represent a third-party liability. Therefore, minimization of these wastes yields a direct cost benefit, both present and future. Measure the quantity and note the composition of any wastes associated with your process that need to be sent for off-site disposal. Record your results in a table or an appropriate spreadsheet. 

Whether you use an audit, a survey, or a combination of both, remember that your results provide a picture of your PSM activities as of a fixed point in time. This creates a useful point of departure for detailed planning, pointing the way toward implementation and establishing a benchmark for future measurement. 

Calculate activation energies for the three Diels-Alder reactions (energy of transition state - sum of energies of reactants). Which reaction has the smallest energy barrier Which has the largest energy barrier Do your results parallel the measured relative rates of the same reactions (see table at left) ... 

Calculate bout IcLtn for the reversible reaction in Example 5.2 in a CSTR at 280 K and 285 K with F=2h. Suppose these results were actual measurements and that you did not realize the reaction was reversible. Fit a first-order model to the data to find the apparent activation energy. Discuss your results. 

Measuring and Using Numbers Convert the volume of NaOH used in mL to L of NaOH and determine the moles of NaOH per liter. Record your result in Data Table 1 as the molarity of NaOH (M). 

List the measures you could take which would help ensure the quality of your work and make your results more reliable. 

Statistics is a branch of mathematics that involves the study of data. Probability is the study of chance. This chapter will refresh your understanding of common statistical measures, graphs, and probability. Before proceeding to the lesson, take this ten-item Benchmark Quiz to see how much you remember about statistics and probability. These questions are similar to the type of questions that you will find on important tests. When you are finished, check the answer key carefully to assess your results. Your Benchmark Quiz analysis will help you determine how much time you need to spend on statistics and probability, and the specific areas in which you need the most careful review and practice. 

What were your independent and dependent variables Did you use a control Did all of the lab teams measure the same variables Were the data that you collected qualitative or quantitative Does this make a difference when reporting your data to others Do your results agree Why or why not ... 

X 10 mol/L FelNOsls, and 0.200 mol/L Fe(N03)3. Pour about 30 mL of each stock solution into its labelled beaker. Be sure to distinguish between the different concentrations of the iron(III) nitrate solutions. Make sure that you choose the correct solution when needed in the investigation. Measure the volume of each solution as carefully as possible to ensure the accuracy of your results. 

When you take measurements and use them to calculate other quantities, you must be careful to keep track of which digits in your calculations and results are significant. Why Your results should not imply more certainty than your measured quantities justify. This is especially important when you use a calculator. Calculators usually report results with far more digits than your data warrant. Always remember that calculators do not make decisions about certainty. You do. Follow the rules given below to report significant digits in a calculated answer. 

At atmospheric pressure (101.325 kPa), a quartz is in equilibrium with (3 quartz at 847 + 1.5K [8]. The enthalpy change of the transition from a quartz to (3 quartz is 728 + 167 J mol Berger et al. [9] measured the volume change by an X-ray diffraction method, and they reported a value of 0.154 + 0.015 cm mol Use these values to calculate the slope at atmospheric pressure of the equilibrium curve between a quartz and 3 quartz in Figure 13.1. Compare your results with the value of the pressure derivative of the equilibrium temperature dT/dP, which is equal to 0.21 K (Mpa) [10]. 

Your record of work, which may be paper-based or electronic, may be presented as your evidence for a record of experimental data. In this regard, you must record all your raw results and the uncertainties associated with each measurement. If you tabulate your results, the tables should have proper headings and the appropriate units. The more information you record as you carry out your project, then the easier it will be to write up a good, comprehensive Project Report later. The number of marks you obtain out of the 30 marks available for the project will be awarded by the marker based purely on what he or she reads in your Project Report. 

Three marks are for the evaluation of your results. The marker will be looking for how well you have analysed and interpreted your results. You may wish to work out the effect on your final calculated results of all the uncertainties in your individual recorded measurements. 

Estimate the diffusivity of toluene in water at 25°C using the Wilke-Chang and the Hayduk-Laudie relationships. Compare your result with measured values in Table 3.7. 

Estimate the diffusion coefficient for 10 compounds through air at 1 atmosphere pressure from the Wilke-Lee adjustment to the Chapman-Enskog theory and compare your results with measurements. What is the percent error of the estimation (assuming that the measurements are correct) What is the primary cause of the differences between the estimated diffusivities ... 

The top-down approach has become the antithesis to the bottom-up GUM approach. Having results from a large number of laboratories, each using the prescribed method, but otherwise changing the analyst, time, location, and equipment gives the greatest possible opportunity for effects to be randomized and therefore contribute to the reproducibility. Can the interlaboratory reproducibility simply be asserted to be the measurement uncertainty of your result Possibly, but not necessarily. Remember the measurement uncertainty is of a result, not a method, and so the uncertainty contributions that have been randomized in the reproducibility should be included,... 

Most of this book deals with measuring chemical concentrations in homogeneous aliquots of an unknown. The analysis is meaningless unless you have collected the sample properly, you have taken measures to ensure the reliability of the analytical method, and you communicate your results clearly and completely. The chemical analysis is only the middle portion of a process that begins with a question and ends with a conclusion. 

A Standard Reference Material is certified to contain 94.6 ppm of an organic contaminant in soil. Your analysis gives values of 98.6, 98.4, 97.2, 94.6, and 96.2 ppm. Do your results differ from the expected result at the 95% confidence level If you made one more measurement and found 94.5, would your conclusion change ... 

Materia balance. If you intend to measure all the anions and cations in an unknown, one sanity check on your results is that the total positive charge should equal the total negative charge. Concentrations of anions and cations in pond water in Figure 26-5 are expressed in p-g/mL. Find the total concentration of negative and positive charge (mol/L) to assess the quality of the analysis. What do you conclude about this analysis ... 

If there is an undetected variable or flaw in an experiment, it doesn t matter how many times the tests are repeated. Measuring your weight on a broken scale is a good example of a flawed procedure—no matter how many times you step on the scale, the weight you measure will be wrong every time. Similarly, had the Antarctic researchers not been careful to make sure the fish in the experimental and control tests were equally hungry and of the same species, their results and conclusions would have been unreliable. 

Use your results from parts (a) and (b) to calculate the residual entropy of ice. The measured value is 3.4J/molK. 

In part B, by how much did your TD film elongate when measured under stress After you let the sample relax for 5 minutes, how much longer was the stretched region compared to the original 2 cm What were your results for the MD sample ... 

Mathematical calculations are an important part of chemistry. You will need your calculation skills to help you investigate many of the topics in this textbook. You will also need calculation skills to communicate your measurements and results clearly when you do activities and investigations. Chemistry, however, is more than measurements and calculations. Chemistry also involves finding and interpreting patterns. This is the focus of the next section. 

Write the steps that will allow you to measure the quantities you need. Design a data table for your results. Include a space for the name of the solute in your solution. 

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