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Tools of Chemistry and Identification of Matter
Tools of Chemistry and Identification of Matter
Learning Objectives:
Learning Objectives:
Upon completion of this experiment, students will have experienced:
(CLO1). Explain basic chemical concepts related to chemical changes, energy, and properties of matter.
(CLO2). Apply the methods of scientific inquiry
(MLO1-1) Utilize algebraic methods, scientific notation, rounding numbers, and significant figure rules in calculations
(MLO1-2)Apply units of mass, temperature, time, length, and derived units, such as volume and density using dimensional analysis to solve problems with single or multiple steps or conversions. Recall the common base SI units of measurement, prefixes, and their associated symbols
(MLO1-3) Evaluate the uncertainty, accuracy, and precision of measurements.
Determine the density using a variety of methods
Perform graphing and interpolation of data
Determine the identity and purity of a substance using physical properties.
Determination of melting point using the capillary technique.
Experiment 2 focuses on the proper representation of data and results and the use of tools with an understanding of precision and accuracy. Physical properties can be used to identify a substance, density, melting point and physical appearance can be used to determine the identity of an unknown substance.
The assignments that must be completed are the following:
The assignments that must be completed are the following:
the pre laboratory writing assignment. This assignment must be submitted before the lab session. This assignment will NOT be accepted late.
Buret Quiz in Canvas. Read the Buret Tutorial before attempting the buret quiz.
Complete the Pre laboratory problems
Complete the Laboratory Report of the experiment using the resources listed below and the data collected in the laboratory session
Complete the Post laboratory problems and Conclusion paragraph using the RERUNS method
Experiment Discussion:
Discussion:
Density is the relationship between the mass of an object and its volume.
Density = mass of the substance / volume of the substance.
Density is a physical property of any substance and often used to identify the materials. The mass of the substance is always measure in grams and the volume of most liquids and solids are measured in either mL or cm3. Therefore the units of density can be written as either g/mL or g/cm3. The density is considered to be the mass of 1 mL or 1 cm3.
Experiment 2 DiscussionIn this experiment, we will determine the accuracy and precision of these two tools in measuring the volume of water.
For example, a single block of wood is measured multiple times by several different students giving the following values of the mass:
Student 1 weighs the block of wood to be 3.56 g
Student 2 weighs the block of wood to be 3.7203 g
Student 3 weighs the block of wood to be 3.682 g
Student 4 weighs the block of wood to be 3.715 g
The four values of the mass are different. The number of decimal places are different most likely because the students used 4 different balances or did not report there mass to the correct significant figures as determined by the precision of the balance.
The average value of the mass is determined to be 3.67 g. The average is rounded to the least significant figures.
Precision can be determined by the number of significant figures reported, therefore, 3.7203 g is more precise than 3.56 g because it has more significant figures and the balance is said to be more precise because it allows the user to read more significant figures in the measurement. However, precision is more often determined by the standard deviation or the average deviation, which shows the reproducibility of the measurement. The smaller the deviations, the more closely the measured values are to each other and the more precise the measurement. The average deviation is a very simple equation where | x | represents the absolute value and Σ represents the sum of all the values. The deviation is simply the absolute value of the difference between the averaged value and the measurement of each students mass.
Deviation = | average value - individual value | (absolute value)
The Average deviation of the 4 students measurements can be determined by averaging the deviations of each measurement from the average:
Deviation of Student 1 = | 3.67 - 3.56 | = 0.11 g
Deviation of Student 2 = | 3.67 - 3.7203 | = 0.05 g
Deviation of Student 3 = | 3.67 - 3.682 | = 0.01 g
Deviation of Student 4 = | 3.67 - 3.715 | = 0.05 g
The average deviation, s,
is 0.05 g
The standard deviation is considered to be a better calculation of the error but we will be using the simpler calculation of average deviation for this lab.
The standard deviation is 0.07 g
Generally, the average or standard deviation is reported with only one significant figure and shows the number of decimal places that should be reported in the final average. Since both the average and standard deviation is rounded to the second decimal place, the average should also be rounded to the second decimal place. The average or standard deviation is relatively small, so we could say that these measurements are fairly precise. However, the smaller the value of the average deviation, the greater the precision of the measurements.
Accuracy is defined to be how close the measured or calculated value is to the true or known value and can be measured by the percent error, which shows how closely the experimental value compared to the true or book value. So if we know the true mass of the block to be 3.956 g, the accuracy can be determined using the following equation.
The percent error of these measurements is determined to be 7 %. Again we often round the percent error to one significant figure, but you can also report the percent error to 7.2%. This is relatively small, good accuracy is considered to have a percent error less than 5%, while poor accuracy is considered to be greater than 10%. Therefore I would consider these measurements to be somewhat accurate.
The average density, deviations, average deviation, and percent error are determined for the two methods. See the above explanation of deviation and average deviation to determine these values for each measurement. The densities of water at the temperature of the water measured, can be looked up in the CRC handbook of Chemistry and physics in the lab or you can look up the value of the density online
Tyler DeWitt videos on Density
Density Practice Problems - https://youtu.be/7tVebi3TSsg
Advanced Density Problem 1 - https://youtu.be/4tYXaCADxfE
Advanced Density Problem 2 - https://youtu.be/TFXC3SV50R0
Advanced Density Problem 3 - https://youtu.be/5tVNGlG1GBc
Once the density is determined, we can use the given density versus % mass data to create a calibration curve, which is then used to extrapolate the calculated density to the % mass in the calibration graph.
Graphing is often used by scientist to determine the accuracy and precision of the experimental data. Often two sets of data (x the independent variable and y the dependant variable) can be graphed resulting in a linear relationship between the two measurements. Often, the data must be manipulated to create a linear relationship, such as taking the inverse of a measurement, the log of the measurement or other simple function. The resulting data can be graphed and the resulting value can be represented by a linear relationship: y = m x + b, where m is the slope of the line and b is the intercept of the line. The slope of the line is easily determined by dividing the rise (the change in the y values) by the run (the change in the x values) of the data points or
A statistical method of determining the slope of the line is linear regression. When drawing a line through the data points, a straight line is used, never a line in which you connect the points. Sometimes, when the line is drawn, some of the data points may not lie directly on the "best fit line". After determining the best fit line, we can extend the length of the line past the points that were actually measured. This is called extrapolation.
We can also use the line to determine value that were not actually measured, by plotting the known values, a calibration curve is created. If one of the values is known, the other can be determined by extrapolating between the data points using the calibration curve. The Microsoft Excel spreadsheet program can be used to plot a linear graph and determine the best fit line by linear regression. The R2 value or correlation coefficient gives the precision of the line or how well the x - y values fit on the "best fit" line as determined by linear regression. We can use this graph then can be used to determine an unknown measurement from the known measurement, this is called extrapolation of data. Or by knowing the value of the slope and intercept of the graphed line, then if you know the value of y, one can calculate the corresponding value of x. Below you see the red lines that allow us to determine the value of x as determined from the best fit line by inspection.
Pre laboratory writing assignment
Pre laboratory writing assignment
The student should complete two assignments before coming to the laboratory discussion. The first is a pre laboratory writing assignment that will be required for most of the laboratory assignments. The pre writing assignment may consist of up to three parts: a purpose statement of what the objectives of the assignment are, a theory paragraph containing background and an understanding of why we are completing this assignment and finally, a summary paragraph of the procedure explaining how the assignment will be completed.
The student should complete a pre laboratory writing assignment for Experiment 2 that contains a summary paragraph of the procedure explaining how the assignment will be completed and a list of the data that must be collected while performing this experiment. A pre writing assignment is included in the example of a formal laboratory report at https://docs.google.com/document/d/1BGBPJS3VqNME4cKDrR50HqqrIYZt0sZ9UCg6IrS3MDk This assignment will only be accepted before the laboratory session begins. No late assignments will be accepted.
Pre laboratory Problems
Pre laboratory Problems
The pre laboratory problems are questions about the laboratory assignment, background, definitions or procedure and calculations. These problems should be completed BEFORE coming to the class where the assignment will be discussed.
Read the Buret Tutorial and complete the Buret quiz in Canvas in Experiment 2 assignments
Procedure and Report
Procedure and Report
Complete the individual parts of this laboratory using the resources given below and in the laboratory assignment.
Part A: Accuracy and Precision
Part A: Accuracy and Precision
The Laboratory Report of the assignment contains questions, data collection, calculation and reporting of results. Use the images of measurement in the full document or in the laboratory report to record the measurements and perform the calculations.
In this experiment, the density of liquids will be determined by measuring the mass and the volume of the liquids. The volume of a liquid can easily be determined by using a tool that measures volume. Graduated cylinders and volumetric pipets are often used but a buret can also be used to determine the volume of a liquid both accurately and precisely. There are several methods that can be used to determine the volume of a liquid. This experiment will compare all three methods, using a graduated cylinder, a volumetric pipet and a buret. Pipets and burets are often used to measure the volume of a liquid that is being transferred while a graduated cylinder is used to determine the volume of a liquid that is not poured out of the container.
Using a buret, a 10 mL graduated cylinder and a 10 mL volumetric pipet will be used to measure the volume of water. so that the density of the water can be determined.
Using Burets and Pipets: the following are several YouTube videos that might be useful.
Accuracy and Precision for Data Collection
Accuracy and Precision for Data Collection
Professor Dave Explains - In science, we love data! But what are the rules of data collection? How accurate and how precise can we get with our data? What do these words even mean? Let's find out!
Reading a Buret: http://youtu.be/RHTxIYDJ730
how to read a graduated cylinder: https://youtu.be/7ewRaV5baik
Proper use of a pipet:
In this experiment, we will determine the accuracy and precision of these two tools in measuring the volume of water.
The average density, deviations, average deviation, and percent error are determined for the two methods. See the explanation in the laboratory discussion of deviation and average deviation to determine these values for each measurement. The densities of water at the temperature of the water measured, can be looked up in the CRC handbook of Chemistry and physics in the lab or you can look up the value of the density by doing a search.
Sites that have the density of water at various temperatures
Appendix M: Physical Properties of Water: https://drive.google.com/open?id=1-ETcY_LkzMKgHACM1Ix6BxeC_aH4UQKQ37BZn-Vt3Ek
http://antoine.frostburg.edu/chem/senese/javascript/water-density.html
This is the book value of the density of water and this value is used to determine the percent error using the Percent Error relationship.
Water density Calculator
The density of pure water is approximately 1 g/mL but it varies slightly with temperature. To determine the accuracy of the tools, the density of water determined from the measurements will be compared to the true value at the temperature measured. You can use the link below or the links given on the introduction page to find the exact density of water with 6 to 7 decimals at your measured temperature.
http://www.csgnetwork.com/h2odenscalc.html
Note: to determine the density of pure water, set the salinity to 0.00
Part B: Density of a Salt Solution
Part B: Density of a Salt Solution
The Laboratory Report of the assignment contains questions, data collection, calculation and reporting of results. Use the images of measurement in the full document or in the laboratory report to record the measurements and perform the calculations for this part of the experiment.
In this part of this experiment, we will determine the density of a salt solution using a 10.00 mL pipet to measure the volume of the unknown salt solution. Use the images to determine the mass of the unknown salt solution A, B or C. Calculate the density of the unknown salt solution.
Once the density is determined, we can use the given density versus % mass data to create a calibration curve, which is then used to interpolate the calculated density to the % mass in the calibration graph.
Part C: Density of a metal cylinder
Part C: Density of a metal cylinder
The Laboratory Report of the assignment contains questions, data collection, calculation and reporting of results. Use the images of measurement in the full document or in the laboratory report to record the measurements and perform the calculations for this part of the experiment.
In this part of the experiment, the density of solids will be determined . The volume is determined either by a method of water displacement or by calculation of the volume of a regularly shaped object such as a sphere or cube.
We will use the calipers and micrometers to measure the length and diameter of a metal cylinder. See Experiment 0 for directions on how to use these tools.
Using the displacement method to determine volume and a linear measurement technique
How to use a Venier Caliper: http://youtu.be/4hlNi0jdoeQ http://youtu.be/ZUNoWWw6V10 https://youtu.be/9DAxslknc-M
How to use a Micrometer: http://youtu.be/i_jygJkJujE in metric: http://youtu.be/O8vMFFYNIfo
How to read a metric ruler: https://youtu.be/GbOu0d18mSg
How to read a micrometer: https://youtu.be/O8vMFFYNIfo
Density of metals:
Part D Melting Point
Part D Melting Point
https://phet.colorado.edu/en/simulation/states-of-matter-basics
Density is one physical property of a substance that can be used to identify an unknown, color, state of matter, and solubility of the substance in water or other liquids can also be used to identify . We will be using the melting point of the substance to determine both its identity and its purity. To determine the melting point of a solid, we will use a melting point apparatus.
Using the melting point apparatus.
Using Melting Point Appuratus: http://youtu.be/fwSHKzyQJK0
How to pack a melting point capillary and measure a melting point:
Melting Point Determination: http://youtu.be/9aQio1KQKrs
Melting Point of an Organic Compound - MeitY OLabs
Melting Point of an Organic Compound - MeitY OLabs
This video channel is developed by Amrita University's CREATE http://www.amrita.edu/create
Copyright © 2013 Amrita University Developed by CDAC Mumbai & Amrita University under research grant from Department of IT, Government of India Melting Point of an Organic Compound :- The melting point is an important physical property of a compound. The melting point can be used to identify a substance and as an indication of its purity. A pure crystalline compound usually possesses a sharp melting point and it melts completely over a narrow range of temperature of not more that 0.5 -1 °C. The presence of even small amount of impurities usually produces a depression in the freezing points and shows a marked increase in the width of the melting point range. The melting point range of greater than 5 °C indicates that the substance is impure. For a material whose identity is known, an estimate of degree of purity can be made by comparing its melting point with that of a pure sample. This video explains how to determine the melting point of an organic compound.
Post Laboratory Problems and Conclusion paragraph
Post Laboratory Problems and Conclusion paragraph
The post laboratory problems contains questions that determine your understanding of the laboratory assignment.
While the conclusion paragraph is a summary of what you learned in the assignment. The conclusion paragraph should not just be "this is what I learned" statement but a summary of the assignment, analysis of the data and results of the assignment and critical thinking about what was learned and why it is important. The RERUN
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