Chemistry 113.1Introduction to Chemical TechniquesExperiment 1. Density(May 2012)INTRODUCTIONDensity (?) is defined as the ratio of the mass (m) of a sample to its volume (V):?=m/VMass and volume are extensive properties of matter-properties that depend on the quantity of asubstance. Such properties are not in themselves useful in characterizing or identifyingsubstances. Intensive properties such as density however are useful in identifying substances.Intensive properties are often determined by taking the ratio of two extensive propertiesmeasured under constant temperature and pressure conditions. As an intensive property densitycan be useful in identifying a substance. Density alone cannot absolutely identify a substance butcan be a useful value contributing to an identification. For example a colorless liquid found tohave a density of 1.00 g/mL at 4 0C and 1.0 atmosphere pressure could be water since this is theknown density of water. Additional information would be needed to absolutely identify thesubstance. In contrast a colorless liquid found to have a density of 0.85 g/mL at 4 0C and 1.0atmosphere pressure could not be water.In the experiments below you will use several methods to determine the volume of samples both solid objects and liquids. You will use the electronic balance to determine the mass of thesamples to 0.001 g (1 milligram). From these measurements you will determine the densities ofthese samples.A. DENSITY OF REGULARLY SHAPED OBJECTSFor regularly shaped objects such as cylinders the volume can be determined by measuring thedimensions of the object with a ruler then applying the proper formula to determine the volume.In this experiment you will determine the density of a group of objects (all cylinders)individually then by a graphical method.1. Obtain one set of cylinders from your instructor. Record the CODE on the container inyour laboratory notebook. Record the color and any other distinguishing characteristics aswell.2. Using the plastic ruler in your kit measure the diameter(d) and the length (or height-h) ofeach cylinder to the nearest 0.5 millimeter (e.g. diameter = 13.5 mm = 1.35 cm).3. Using the electronic balance assigned to you determine the mass of each cylinder to thenearest milligram (0.001 g).4. Using the measured diameter and length calculate the volume of each cylinder in cm3.V= pr2h = p(d/2)2h?1? Chemistry 113.1Introduction to Chemical TechniquesExperiment 1. Density(May 2012)5. Calculate the density r of each cylinder. Report the calculated value for each cylinder aswell as the value of the mean (average). [See the addendum regarding the mean andmean absolute deviation. These should always be reported whenever three or moredeterminations of the same quantity are the result of identical experiments.]6. Graph the data for the cylinders with the mass (g) as the y-axis and the volume (cm3) asthe x-axis. Using the straight line fitting function of the graphing software find theformula corresponding to the best fit of the graphed points to a straight line. The slope ofthis line is the density (?m/?V). Report this value. Compare it to the average densityreported in (5) above.B. DENSITY OF IRREGULARLY SHAPED OBJECTSIf an object has and irregular shape its volume can be determined using Archimedes’ principlewhich states: An insoluble body completely submerged in a fluid displaces its own volume.Thus the volume of the displaced fluid is equal to the volume of the irregularly shaped object.1. Obtain a set of mineral samples from your instructor. Record the code identifying thesample in your laboratory notebook. Note any distinguishing characteristics of theminerals such as color shape etc.2. Using the electronic balance record the mass of the samples to the nearest milligram(0.001 g).3. Place approximately 30.0 mL of water in the 100 mL graduated cylinder. Record theexact volume to the nearest 0.1 mL.4. Carefully add the sample or samples to the water in the graduated cylinder withoutcausing any water to be lost by splashing. Note: It may be best to determine thecombined volume of 2 or more pieces of mineral together. As long as the samples arecompletely submerged the greater the increase in volume for the water in the graduatedcylinder the more precise the measurement of density will be.5. Remove the samples from the cylinder dry them with a paper towel return them to thestorage container and return them to your instructor.6. Calculate the density (?) of the mineral sample.C. DENSITY OF LIQUIDS: CONSTRUCTING A CALIBRATION CURVE AND DETERMINING V%COMPOSITION OF AN UNKNOWN SAMPLEIn this experiment you will prepare a series of liquid mixtures of known composition (percent byvolume or V%) and determine their densities. Using your graph of density versus V% you willdetermine the V% of an unknown sample by measuring its density and comparing it to thegraphed values.?2? Chemistry 113.1Introduction to Chemical TechniquesExperiment 1. Density(May 2012)1. Using a small beaker obtain about 10 mL of alcohol (either methanol or ethanol). Recordthe name of the alcohol used.2. Place a clean dry 10 mL graduated cylinder on the electronic balance and tare it to 0.000g.3. Carefully transfer 2 mL of the alcohol into the graduated cylinder. Read and record theexact volume to the nearest 0.1 mL. [ Note: When reading the volume the level beingread should be at eye level.]4. Record the mass of the alcohol. Using the mass and volume calculate the density andenter it in the data table.5. Add 1 mL of distilled water to the alcohol in the cylinder. Record the exact total volumenow in the cylinder and total mass. [Note: Total volume should now be about 3.0 mL]6. Add 2 additional mL of distilled water to the contents of the cylinder (the total volume atthis point should be approximately 5 mL total). Record the exact total volume and thetotal mass.7. Add 2 additional mL of distilled water to the contents of the cylinder (the total volume atthis point should be approximately 7 mL total). Record the exact total volume and thetotal mass.8. EMPTY the graduated cylinder and dry it.9. At this point you may need to place the cylinder on the balance and tare to 0.000g onceagain. Then-add 2 mL of distilled water to the graduated cylinder and record the exactvolume and the mass to 0.001 g. Divide the recorded mass of the water by its volume.The value should be 1.00 g/mL which is the known density of water. If this is not thecase consult with your instructor immediately.Obtain a sample of alcohol/water of unknown (to you) V% composition . Determine the volumeand mass of two individual 3 to 4 mL portions (known as aliquots) of this sample. Record theexact volume and mass of these two aliquots.?3? Chemistry 113.1Introduction to Chemical TechniquesExperiment 1. Density(May 2012)RECORDING DATAIn your laboratory notebook you should record all data in a format similar to the suggestedformats below:A. DENSITY OF REGULARLY SHAPED OBJECTSSample Code __________________Description:Table A. The dimensions and mass of each object.ObjectDiameter (cm)Length or Height (cm)Mass (g)ABCDNote: In your laboratory report this data should be transcribed into a neatly typed table. A finalcolumn should be added giving the calculated value of density ? in g/cm3.Using the tabulated values above prepare a graph of mass(g) (y-axis) versus volume (cm3) (xaxis). A straight line fit has a slope equal to the density of the sample [slope = ?m/?V]. Reportthis value of the determined density. Using the table of Materials and their Densities provided can you identify the material ?B. DENSITY OF IRREGULARLY SHAPED OBJECTSTable B. The mass (or combined masses) of the mineral sample(s) the initial volume of water inthe graduated cylinder [Vi (H2O)] the final volume after addition of the sample(s) [Vf (H2O)] and the volume of the sample(s) Vmineral.M (g)[Vi (H2O)] (mL)[Vf (H2O)] (mL)Vmineral (mL)Note: In your laboratory report this data should be transcribed into a neatly typed table. A finalcolumn should be added giving the calculated value of density ? in g/cm3. [Recall that 1 mL=1cm3]. Using the provided table of mineral densities and descriptions can you tentatively identifythe mineral you were assigned ??4? Chemistry 113.1Introduction to Chemical TechniquesExperiment 1. Density(May 2012)C. DENSITY OF LIQUIDS: CONSTRUCTING A CALIBRATION CURVE AND DETERMINING VOLUMEPERCENT (V%) COMPOSITION OF AN UNKNOWN SAMPLE(1) The alcohol used in this experiment was ____________________(2) The V% for this alcohol is _______________________[Note: ethyl alcohol (ethanol) is 95% by volume ethanol and 5% water]Table C1. Volume of alcohol Valcohol volume of added water Vwater total volume Vtotal totalmass m and volume percent alcohol V%alcoholSample1ValcoholAt start (onlyentry)Vwater addedVtotalmass totalV%alcohol2345 (water only)The volume percent (V%) is equal to: 100 x (Valcohol / Vtotal ). For example if 2.0 mL of 95V%ethanol is initially present then for a Vtotal of 5.0 mL (after addition of 1 and then 2 mL ofwater):V%ethanol = 100 x(0.95 x 2.0) / (5.0) =38%Note: In your laboratory report this data should be transcribed into a neatly typed table. A finalcolumn should be added giving the calculated value of density ? in g/mL for each value ofV%alcohol.In your report you will graph the values of density (g/mL) (y-axis) versus V% (x-axis) andprovide a straight line fit to the points on the graph.Table C2. Volume V and mass m of two aliquots of alcohol/water mixture of unknown V%.VolumeMassDensity (r)aliquot #1:aliquot #2:Using the graph of density (g/mL) (y-axis) versus V% (x-axis) which you have prepared determine and report the V% of each of the two aliquots.?5? Chemistry 113.1Introduction to Chemical TechniquesExperiment 1. Density(May 2012)A. TABLE OF MATERIALS AND THEIR DENSITIESMaterialDensity(g/cm3)aluminumteflonpolyvinyl chloridephenolicpolyurethaneacrylicnylonpolypropylene2.712.201.371.321.231.171.150.90B. TABLE OF MINERAL DENSITIES AND DESCRIPTIONSDensity(g/mL)5.04.94-5.072.75-2.794.013.122.93descriptionmetallic brassy crystallinemetallic graylight blue with white and yellow-browndark brown with red highlightsblackblue with white2.832.712.692.592.582.532.36?dark brown with paler gold and white streakspurple and hitelight brown with paler gold and white streakslight gray with blackturquose (light) with whitelight blue with white and brownroyal blue with white veining6?Probable IDFeS2 pyritehematite a-Fe2O3aquamarineAlamndine garnetSchorl tourmalinelapis lazulitiger eye microcrystalline SiO2 withiron oxideamethyst SiO2 with Fe impuritiescitrineLabradoriteamazonitechrysoprasesodalite Na4Al3(SiO4)3Cl Chemistry 113.1Introduction to Chemical TechniquesExperiment 1. Density(May 2012)LABORATORY REPORT SUGGESTIONS FOR THIS LABORATORYIn addition to the more general instructions posted on Blackboard here are some specific tipswith reference to the Density experiments:Abstract• One sentence defining density• One sentence stating the results of the regular shaped object density determination• One sentence stating the results of the irregularly shaped object(s)-minerals densitydetermination• One sentence or two giving the results of the density of liquids experiments including thevolume percent (V%) of the unknown mixtureIntroduction• Explain the difference between intensive and extensive properties and why one is usefulin characterizing materials• Explain density with the equations defining all variables or symbols usedExperimental• Summarize the procedures for regularly shaped objects• Summarize the procedures for irregularly shaped objects• Summarize the procedures for density of liquids including the unknown sample.Results/Discussion• Tables of data should be neatly transcribed from the data sheets in your laboratorynotebook adding where needed values (such as density) calculated from the data.• Provide a sample calculation of each type of calculated value (but not every one).• Show the graphs for density of regular shaped objects (A) and volume percent as afunction of density (C). State the slope for each and what it signifies.• In the appropriate section provide the tentative ID for the material of the regularlyshaped objects (cylinders) and explain your reasoning. Do the same for the irregularlyshaped object(s) with appropriate reasoning. In each case provide an estimate of theuncertainty in the reported density values with explanation.• Report the value of the V% for the unknown alcohol-water mixture with uncertainty.?7? Chemistry 113.1Introduction to Chemical TechniquesExperiment 1. Density(May 2012)ADDENDUMREPORTING THE MEAN AND MEAN ABSOLUTE DEVIATIONCalculating the Mean density and Mean Absolute Deviation1) Determine the Mean: Add all numbers and divide by the count (3)Example: the density of three cylinders denoted by letters are found to be:A : 1.6 g/cm3B : 2.0 g/cm3C : 1.8 g/cm3Mean = (1.6 1.8 2.0)/3 = 1.8 g/cm32) Determine deviation of each result from the Mean ( individual value – Mean)1.6 – 1.8 = – 0.21.8 – 1.8 =0.02.0 – 1.8 = 0.23) Eliminate the or – sign and take the mean of the absolute deviationsThus the Mean Absolute Deviation is (0.2 0.0 0.2)/3 =0.13 g/cm3 round to 0.1 g/cm3Report the density as 1.8 /- 0.1 g/cm3 [Alternatively you can use the Excel formula=AVEDEV(1.6 2.0 1.8) to obtain the result. ]?8? Chemistry 113.1Introduction to Chemical TechniquesExperiment 2. Hydrate Composition(May 2012)I. INTRODUCTIONThe law of definite (or multiple) proportions states that when two or more elements combine toform a given compound they do so in fixed proportions by mass. For example sodium chloridecontains 39.3% by mass sodium and 60.7% by mass chlorine. In these experiments the law ofdefinite proportions will be used to determine the empirical formulas of hydrated ionic salts. Anempirical formula expresses the simplest whole number ratio of atoms or units in a compound.(For ionic compounds or hydrates the unit can be a polyatomic anion or water.)Hydrates are substances formed when water combines chemically in definite proportionswith an ionic salt thereby giving a constant ratio of water molecules to the ions of the salt.Hydrates are not mixtures since the water is coordinatively (covalently) bound to either thecation or anion or both in the salt. In CuSO4 • 5 H2O for example the bonding involves fourwater molecules coordinatively bound to the Cu2 ion in a square planar structure and onemolecule of water bound to the sulfate ion by hydrogen bonds. The anhydrous (without water)form of a hydrated salt is produced when all the waters of hydration are lost. Some examples ofhydrates are listed below:Formula2 CaSO4 • H2OCaSO4 • 2 H2OCuSO4 • 5 H2OMgSO4 • 7 H2ONa2CO3 • 10 H2OCommon nameplaster of Parisgypsumblue vitriolEpsom saltWashing sodaThe • in the formula indicates a kind of chemical bond that usually can be easily broken. Forexample magnesium sulfate heptahydrate can be converted to anhydrous magnesium sulfate byheating:MgSO4 • 7 H2O (s) ? MgSO4 (s) 7 H2O (g) .In this chemical reaction equation (or chemical equation) the (s) indicates a solid and the (g)indicates a gas. In the appendix more details about this reaction equation will be given alongwith how these equations are balanced and how they can be used to predict products of reactions.In this experiment you will heat various hydrated salts to determine the number of watermolecules in the salt.?1? Chemistry 113.1Introduction to Chemical TechniquesExperiment 2. Hydrate Composition(May 2012)II. PROCEDUREObtain from the instructor a hydrated salt chosen from copper sulfate calcium sulfate andmagnesium sulfate. The difference in the mass of the anhydride and the hydrate will then beused to determine the mass of water in the hydrate and therefore the empirical formula of thehydrate. The procedure which should be performed on two samples of the same hydrate is asfollows:1. Weigh a clean dry labeled crucible. Record the weight in your notebook.2. Introduce about 1 – 2 grams of the pulverized hydrated salt. Note the appearance andcolor of the solid.3. Weigh the crucible and contents. Record this weight in your laboratory notebook.4. Setup a wire triangle on the iron ring over a Bunsen burner. (Ensuring that the wiretriangle will hold the crucible in an upright position.)5. Watch the instructor demonstrate how to setup and properly light a Bunsen burner andhow to turn-off the burner after use. (Be sure to record this in your notebook for laterreferral.)6. Heat the crucible and contents in the hottest part of the flame for 5 – 10 minutes. (Thebottom of the crucible should turn a dull red during heating.) Initially the hydrate shouldbe heated slowly by waving the burner flame fairly rapidly under the crucible. If thematerial begins to boil or crackle the heating is too intense and splattering may occur.Within approximately 1 minute the material should become drier and stronger heat canbe applied. At the end of the 5 – 10 minute period of heating allow the crucible to coolslightly before transfer.7. Using clean crucible tongs transfer the crucible to a desiccator and allow the crucible tocool to room temperature.8. When cool weigh the dish and the anhydride and record this weight in your notebook.9. Heat the crucible in the flame again for 5 minutes place in desiccator and allow thecrucible to cool. Once cool weigh the sample again. Continue the heat/cool/weigh cycleuntil the mass of the sample remains constant. Be sure to record all of yourmeasurements in your notebook.10. Place a thermometer in the anhydrous salt and record the temperature.11. Add a few drops of water to the anhydrous salt near the thermometer and record thetemperature (once the temperature has stopped increasing). This temperature changerepresents the change from an anhydrous salt to a hydrated salt.Remember: Write the experimental procedures that YOU followed while you were doingthe experiment. Be sure to note if the salt splattered or popped out of the crucible whileheating. These types of observations will be important when discussing sources ofexperimental error.?2? Chemistry 113.1Introduction to Chemical TechniquesExperiment 2. Hydrate Composition(May 2012)Useful information that should be recorded in the notebook at some point during the experiment:•••Name of salt and formulaQualitative description of the salt before and after heating.Temperature of the salt before and after the addition of waterTable 4.1. Masses m in grams (g) necessary to determine the composition of the salt from thefirst trial.Objectm (g)NotesClean dry crucibleCrucible with salt (beforeheating)Crucible with salt after 1stheat/cool cycleCrucible with salt after 2ndheat/cool cycleCrucible with salt after 3rdheat/cool cycle (or until stable)Crucible with salt after 4thheat/cool cycle (or until stable)Crucible with salt after 5thheat/cool cycle (or until stable)?3? Chemistry 113.1Introduction to Chemical TechniquesExperiment 2. Hydrate Composition(May 2012)Table 4.2. Masses m in grams (g) necessary to determine the composition of the salt from thesecond trial.Objectm (g)NotesClean dry crucibleCrucible with salt (beforeheating)Crucible with salt after 1stheat/cool cycleCrucible with salt after 2ndheat/cool cycleCrucible with salt after 3rdheat/cool cycle (or until stable)Crucible with salt after 4thheat/cool cycle (or until stable)Crucible with salt after 5thheat/cool cycle (or until stable)?4? Chemistry 113.1Introduction to Chemical TechniquesExperiment 2. Hydrate Composition(May 2012)III. POST-LABORATORY DISCUSSION AND QUESTIONSThe mass of a single atom is difficult to measure. (For instance the mass of a single hydrogencation (or proton) is 1.67 × 10-24 g.) Therefore the mole is defined as the number of 12C atoms inexactly 12 grams of 12C. Moreover the basic unit of mass for elemental chemistry namely theatomic mass unit (amu or dalton) is defined as 1 amu = 1/12 the mass of an atom of 12C = 1.6605× 10-24 g. Thus The constant 6.022 × 1023 atoms (or molecules)/mole is known as Avogadro’s number NA. Sincethe mole and the atomic mass unit are defined using the same scale 1 amu × NA = 1 g/mole.Thus the masses given on the periodic table can also be expressed as the number of grams of theelement per mole of element. The molar mass M of a compound is obtained by summing themass of all of the elements in a compound and therefore has units of g/mol. Moreover thedefinition of a mole when combined with the law of definite proportions implies that a sample ofH2O will have 2 moles of atomic hydrogen for every 1 mole of atomic oxygen while a sample ofMgF2 has a mole ratio of 1 mole of magnesium for 2 moles of atomic fluorine.Please note that moles are used as the universal conversion factor in chemistry. Thechemical reaction equation written in the introduction for instance can now be read as follows:1 mole of solid magnesium sulfate heptahydrate decomposes with heating to generate onemole of solid magnesium sulfate and 7 moles of gaseous waterThus please become more familiar with this difficult concept by reading about the mole in astandard freshman chemistry book or on Wikipedia. Also in the future when in doubt convert to moles! The post-laboratory questions below will help guide you in the conversionsbetween mass in grams and moles of compound and will show you how this allows you todetermine an empirical formula for a hydrate.?5? Chemistry 113.1Introduction to Chemical TechniquesExperiment 2. Hydrate Composition(May 2012)POST-LABORATORY QUESTIONSWhere appropriate these questions should be answered for each trial. Remember do notwrite Question 1 and then an answer. Also remember to show all work for the calculationsfor one of the trials.1. Determine the mass mh of the hydrated salt by subtracting the mass of the empty cruciblefrom the mass of the salt and the crucible before heating.2. Determine the mass ma of the anhydrous salt by subtracting the mass of the emptycrucible from the mass of the salt and the crucible after the heat/cool cycles are complete.3. The difference in the mass of the hydrated salt and the anhydrous salt is the mass of waterpresent in the sample. Why is the mass different (i.e. what happened to the water)?4. Calculate the molar mass of water.5. Calculate the moles of water in the hydrated salt by dividing the mass of water by themolar mass of water.6. Calculate the molar mass of the anhydrated salt. (To do this use the chemical formulayou wrote from the name of the compound that you used.)7. Calculate the moles of the anhydride in the sample by dividing the mass of the anhydrideby the molar mass of the anhydride.8. Determine how many moles of water are associated with a single mole of anhydride bydividing the moles of water by the moles of anhydride. What is the average value for thisratio?9. Using the information write the formula of the hydrated salt in the formAnhydride • x H2O where x is the average value obtained in question 810. Is x an integer to the correct precision? If not why? What sources of error could havecaused x not to be an integer?11. Lookup your salt on Wikipedia. Is x in Question 9 an appropriate value based on thepossible hydrates that your salt can form? What is the percent error in your value assuming that the information on Wikipedia for the hydrate is correct??6? Chemistry 113.1Introduction to Chemical TechniquesExperiment 3. Precipitation reactions(May 2012)I. INTRODUCTIONIn Experiment 3 you applied heat from a Bunsen burner to decompose a hydrate into ananhydrous salt and gaseous water. A decomposition reaction is one of four broader categories ofchemical reactions. The remaining categories are precipitation reactions acid/base reactions and oxidation/reduction reactions. In this experiment you will investigate precipitationreactions. In a precipitation reaction two aqueous solutions of soluble salts are mixed and yieldan aqueous solution of a soluble salt and a solid compound. The formation of the solid is calledprecipitation and the solid is called the precipitant.When ionic compounds dissolve in water the water interacts with the cation and anion toweaken the Coulombic interaction holding the two ions together as a solid. Thus as the ionsbreak apart because of water surrounding the…I am taking Chem 1 and I am doing my first lab on Density. I am having issues with one section of the lab. I am given two different Aliquots (Unknowns) I’m instructed to determine the V% of each Aliquot. My Figures are as follows Aliquot #1 Mass = 2.219 (g) Volume 3.0 ML Density = .74 g/ml Aliquot # 2 Mass 2.795 (g) Volume 4.0 ML Density = .70 G/ml – How do I calculate the Volume % for these Aliquots? I was given a formula V% = 100 x (V alcohol / V total) but from what I gather I only know the V total.The entire lab document is attached my question pertains to page 5 Table C 2 Any help would be greatly appreciated
