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Useful
Formulas for Experimental Calculations: %Yield, %Error, etc.
Chemistry
110 Supplemental Information
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Useful
Formulas for Experimental Calculations: %Yield, %Error, etc.
The information contained here is supplemental to the material in the experimental protocols packet for this course. These addenda are intended to augment, not replace, the published protocols. These supplements should help you understand the lab experiment better, and, in a few cases, provides answer sheets and worksheets for some experiments. (To view supplemental information click on the experiment name)
Exp I: Separation of a Mixture
Pure substances are either element or compounds. Compounds have fixed composition but mixtures can have virtually any combination of the different pure substances which make them up. For example, brass is composed of about 70% copper and 30% zinc, but the proportions of each metal can vary, and still be called brass. In contrast, a pure substance, such as water (H2O) always has the same composition -- two atoms of hydrogen are combined with one atom of oxygen -- never any other combination (the Law of Constant Composition). As long as you don't perform a chemical reaction to change the chemical nature of the components of a mixture, you can usually separate the different components of the mixture into pure substances.
Exp II: Measurements and Graphing
During the first day of this lab, you will measure the diameter of a set of steel balls (ball bearings) and a set of wooden balls. You will also determine the corresponding mass for each of these balls. You will also use several different measuring containers to measure out 40 mL of water. For this part of the experiment, you will use a 100-mL (or 150-mL) beaker, a 100-mL graduated cylinder, a 50-mL graduated cylinder, and a 10-mL graduated cylinder. From these measurements, you will determine which measuring device gives you the most accurate results.
Exp III: Counting and Measuring Atoms
This experiment involves taking measurements and ultimately determining the radius of a single Al atom or a glucose molecule. There is an Answer Sheet for your to record your data, but you must print this sheet from online.
Exp IV: Chemical Changes: Reactions of Copper
This experiment involves starting with copper, dissolving copper in concentrated nitric acid, and through a sequence of reactions producing metallic copper. This addendum describes the mechanisms of doing the experiment, including the filtrations, mixing of reagents, and the ultimate production of copper.
For this experiment, you will synthesize a new compound, or set of compounds, from the starting reactants. Use only the quantities of material listed in the handout. Determine the limiting reactant which determines your theoretical yield. Be certain that you can identify the correct limiting reactant, and disregard compounds that are used as solvent and which are not present in the product.
For Part A of the experiment, you will prepare Tris(2,4-pentanedionato)iron(III), which is an intense blood-red color. This reaction is similar to the interaction of iron with oxygen in blood, which, of course, is blood red. After you initially synthesize your product, you will purify your product by performing a recrystallization step. Recrystallization is a technique used to purify product, away from any contaminating components. Recrystallization does, however, reduce your yield, but produces a more pure product.
During Part B (optional experiment, depending on your instructor) you will prepare tris(ethylenediamine) nickel(II) chloride. This compound is colored, but not red like the experiment in Part A.
Exp VI: Titration - Determination of Acetic Acid in Vinegar
This instruction sheet describes how to prepare your NaOH solution for all your titration experiments. In addition, this sheet explains how you will standardize your NaOH solution using KHP (potassium hydrogen phthalate) as your acid. Once you have performed your manual titrations (NaOH and KHP) you can calculate the concentration of your NaOH solution for the next part of the experiment, which is the computer-assisted titration of acetic acid.
Download the Titration Data Sheet you will use for all your titration experiments, both manual and using ChemWorks. This data sheet is an Adobe Acrobat file, and you will need Acrobat Reader (free online) to view and print.
Exp VII: Ideal Gas Law: Determination of Gas Constant R & Molar Mass
You will experimentally determine the Universal gas constant, R, expressed in Liters, torr, moles and Kelvin. Use the pressure in torr throughout. If you want to determine the value for R using atmospheres as the pressure term, convert the above R determined above (L•torr/mol•K) into atmospheres (1 atm = 760 torr; L•atm/mol•K).
To determine experimentally the molar mass of a compound, you will follow the basic procedure used to determine R, but solve the Ideal Gas equation for molar mass. I know, the Ideal Gas equation does not contain molar mass, but you can express it as a function of molar mass easily, since moles = grams/molar mass.
Exp VIII: Thermochemistry - Enthalpy of Neutralization
In this experiment you will mix an acid (hydrochloric, sulfuric or phosphoric acid) and a base (NaOH) and measure the heat of reaction (enthalpy of neutralization; ΔHrxn) for this titration reaction. After you determine the amount of heat produced in your experiment, you will calculate the heat produced for each mole of water formed.
Exp IX: Atomic Emission Spectroscopy - Determination of Rydberg Constant
In this experiment, you will determine the Rydberg constant using the line spectrum for hydrogen. Because the spectroscopes may lose their calibration, you will actually perform a calibration step, to correlate the experimental readings with the actual wavelengths for your experiment. You will use a Hg discharge lamp to perform this calibration. Once you have a calibration curve (actually a straight line), you will use the formula for this line to adjust your experimentally determined wavelengths to give a more accurate set of wavelengths. For example, if you had a scale that always read 10 pounds light, while you might feel good because you don't weight as much, your weight is not accurate. Therefore, the weights you measure on your scale need to be adjusted by 10 pounds to give the correct values. This calibration curve allows you to adjust your measured values to the more correct values.
Exp X: Periodic Properties of the Elements
This experiment allows you to examine the elements and to predict periodic trends. You will first examine samples of different elements and make observations based on color, state of matter, etc. to characterize them. For your experimental section, you will do experiments and come to conclusions about elements in the groups you are examining. For the halogen part of the experiment (performed during the first day) you will determine the order of oxidizing strength of the different halogens.
Exp XI: VSEPR - molecular models
These suppplemental pages describe what VSEPR is, and how to use VSEPR to make molecular models, how to predict molecular shapes (molecule geometry), and how to predict molecule polaity, based on the number of electron domains and their arrangement around the center atom. Please note, that an electron domain is a single electron region, a pair of electrons (either lone pairs or bonded pairs), multiple pairs of electrons (such as double and triple bonds).
You should print a table using VSEPR to predict molecule geometry (shape), polarity, and electron domain arrangments for molecules having Three to Six Electron Domains. This table is more complete than the table found in your experimental protocols.
A supplemental worksheet, with different molecules is available online for you to practice on.
For this experiment, you will answer the question, What is a Flame?. You will need to propose to at least five hypotheses to be tested, using the scientific method. These hypotheses must be approved by your instructor during the first day of this lab. You will work with your usual lab partner. If you need any specialized equipment or chemicals not shown below, you need to request these from the stockroom by filling out the check out form prior to the lab period you will need the items, not the same day you need them.
After you have performed your experiments and answered your hypotheses, you must report your results in a formal written lab report (format for this written lab report is available online). You must also turn in your lab notebook, which must be well-written, legible and easy to follow your experimental approach. Your lab notebook and the formal written lab report will be graded. The written lab report is worth a total of 50 points (your lab notebook scores for the entire semester are worth 100 points), so your written lab report is a big part of your lab grade.
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Copyright © Donald L. Robertson (Modified: 09/20/2006)