Laboratory manual for principles of general chemistry 9th edition 2

exp14.qxd 9/1/10 3:42 PM Page 187 Figure 14.5 Determining the mass of beaker and test tube before (Part A.2) and after adding cyclohexane (Part B.1) Figure 14.6 Transfer of the unknown solid solute to the test tube containing cyclohexane Three freezing point trials for the cyclohexane solution are to be completed Successive amounts of unknown sample are added to the cyclohexane in Parts B.4 and B.5 Measure the mass of solvent and solid solute Dry the outside of the test tube containing the cyclohexane and measure its mass in the same 250-mL beaker On weighing paper, tare the mass of 0.1–0.3 g of unknown solid solute (ask your instructor for the approximate mass to use) and record Quantitatively transfer the solute to the cyclohexane in the 200-mm test tube (Figure 14.6).4 Record data for the freezing point of solution Determine the freezing point of this solution in the same way as that of the solvent (Part A.3) Record the time and temperature data on page of the Report Sheet When the solution nears the freezing point of the pure cyclohexane, record the temperature at more frequent time intervals (ϳ15 seconds) A “break” in the curve occurs as the freezing begins, although it may not be as sharp as that for the pure cyclohexane Plot the data on the same graph Plot the temperature versus time data on the same graph (and same coordinates) as those for the pure cyclohexane (Part A.4) Draw straight lines through the data points above and below the freezing point (see Figure 14.3); the intersection of the two straight lines is the freezing point of the solution Repeat with additional solute Remove the test tube and solution from the ice–water bath Add an additional 0.1–0.3 g of unknown solid solute using the same procedure as in Part B.1 Repeat the freezing-point determination and again plot the temperature versus time data on the same graph (Parts B.2 and B.3) The total mass of solute in solution is the sum from the rst and second trials Again Repeat with additional solute Repeat Part B.4 with an additional 0.1–0.2 g of unknown solid solute, using the same procedure as in Part B.1 Repeat the freezing-point determination and again plot the temperature versus time data on the same graph (Parts B.2–4) The total mass of solute in solution is the sum for the masses added in Parts B.1, B.4 and B.5 You now should have four plots on the same graph B Freezing Point of Cyclohexane plus Unknown Solute Appendix C In the transfer, be certain that none of the solid solute adheres to the test tube wall If some does, roll the test tube until the solute dissolves Experiment 14 187 exp14.qxd 9/1/10 3:42 PM Page 188 Obtain instructor’s approval Have your instructor approve the three temperature versus time graphs (Parts B.3–5) that have been added to your rst temperature versus time graph (Part A.4) for the pure cyclohexane Disposal: Dispose of the waste cyclohexane and cyclohexane solution in the Waste Organic Liquids container CLEANUP: Safely store and return the thermometer Rinse the test tube once with acetone; discard the rinse in the Waste Organic Liquids container From the plotted data, determine ⌬Tf for Trial 1, Trial 2, and Trial Refer to the plotted cooling curves (see Figure 14.3) From kf (Table 14.1), the mass (in kg) of the cyclohexane, and the measured ⌬Tf, calculate the moles of solute for each trial See equations 14.1 and 14.3 Determine the molar mass of the solute for each trial (remember the mass of the solute for each trial is different) What is the average molar mass of your unknown solute? Calculate the standard deviation and the relative standard deviation (%RSD) for the molar mass of the solute C Calculations The Next Step NOTES 188 AND Salts dissociate in water (1) Design an experiment to determine the percent dissociation for a selection of salts in water—consider various concentrations of the salt solutions Explain your data (2) Determine the total concentration of dissolved solids in a water sample using this technique and compare your results to the data in Experiment CALCULATIONS Molar Mass of a Solid exp14.qxd 9/1/10 3:42 PM Page 189 Experiment 14 Prelaboratory Assignment Molar Mass of a Solid Date Lab Sec Name Desk No This experiment is more about understanding the colligative properties of a solution rather than the determination of the molar mass of a solid a De ne colligative properties b Which of the following solutes has the greatest effect on the colligative properties for a given mass of pure water? Explain (i) 0.01 mol of CaCl2 (an electrolyte) (ii) 0.01 mol of KNO3 (an electrolyte) (iii) 0.01 mol of CO(NH2)2 (a nonelectrolyte) A 0.194-g sample of a nonvolatile solid solute dissolves in 9.82 g of cyclohexane The change in the freezing point of the solution is 2.94ЊC a What is the molality of the solute in the solution See Table 14.1 and equations 14.1 and 14.3 b Calculate the molar mass of the solute to the correct number of signi cant gures c The same mass of solute is dissolved in 9.82 g of t-butanol instead of cyclohexane What is the expected freezingpoint change of this solution? See Table 14.1 Experiment 14 189 exp14.qxd 9/1/10 3:42 PM Page 190 Explain why ice cubes formed from water of a glacier freeze at a higher temperature than ice cubes formed from water of an underground aquifer Two students prepare two cyclohexane solutions having the same freezing point Student uses 26.6 g of cyclohexane solvent, and student uses 24.1 g of cyclohexane solvent Which student has the greater number of moles of solute? Show calculations Two solutions are prepared using the same solute: Solution A: 0.27 g of the solute dissolves in 27.4 g of t-butanol Solution B: 0.23 g of the solute dissolves in 24.8 g of cyclohexane Which solution has the greatest freezing point change? Show calculations and explain Experimental Procedure a How many (total) data plots are to be completed for this experiment? Account for each b What information is to be extracted from each data plot? 190 Molar Mass of a Solid exp14.qxd 9/1/10 3:42 PM Page 191 Experiment 14 Report Sheet Molar Mass of a Solid Date Lab Sec Name Desk No A Freezing Point of Cyclohexane (Solvent) Mass of beaker, test tube (g) Freezing point, from cooling curve (ЊC) Instructor’s approval of graph B Freezing Point of Cyclohexane plus Unknown Solute Unknown solute no _ Trial (Parts B.1, B.3) Trial (Part B.4) Trial (Part B.5) Mass of beaker, test tube, cyclohexane (g) _ Mass of cyclohexane (g) _ Tared mass of added solute (g) _ _ _ Freezing point, from cooling curve (ЊC) _ _ _ Instructor’s approval of graph _ Calculations kf for cyclohexane (pure solvent) 20.0 ЊC • kg/mol Freezing-point change, ⌬Tf (ЊC) _ _ _ Mass of cyclohexane in solution (kg) _ _ _ Moles of solute, total (mol) _ _ _ Mass of solute in solution, total (g) _ _ _ Molar mass of solute (g/mol) _ _* _ Average molar mass of solute _ Standard deviation of molar mass _ Appendix B Relative standard deviation of molar mass (%RSD) _ Appendix B *Show calculation(s) for Trial on the next page Experiment 14 191 exp14.qxd 9/1/10 3:42 PM Page 192 *Calculations for Trial A Cyclohexane Time B Cyclohexane ؉ Unknown Solute Trial Temp Time Trial Temp Time Trial Temp Time Temp Continue recording data on your own paper and submit it with the Report Sheet Laboratory Questions Circle the questions that have been assigned Part A.3 Some of the cyclohexane solvent vaporized during the temperature versus time measurement Will this loss of cyclohexane result in its freezing point being recorded as too high, too low, or unaffected? Explain Part A.3 The digital thermometer is miscalibrated by ϩ0.15ЊC over its entire range If the same thermometer is used in Part B.2, will the reported moles of solute in the solution be too high, too low, or unaffected? Explain Part B.1 Some of the solid solute adheres to the side of the test tube during the freezing point determination of the solution in Part B.2 As a result of the oversight, will the reported molar mass of the solute be too high, too low, or unaffected? Explain Part B.2 Some of the cyclohexane solvent vaporized during the temperature versus time measurement Will this loss of cyclohexane result in the freezing point of the solution being recorded as too high, too low, or unaffected? Explain Part B.2 The solute dissociates slightly in the solvent How will the slight dissociation affect the reported molar mass of the solute—too high, too low, or unaffected? Explain *6 Part B.3, Figure 14.3 The temperature versus time data plot (Figure 14.3) shows no change in temperature at the freezing point for a pure solvent; however, the temperature at the freezing point for a solution steadily decreases until the solution has completely solidi ed Account for this decreasing temperature Part C.1 Interpretation of the data plots consistently shows that the freezing points of three solutions are too high As a result of this “misreading of the data,” will the reported molar mass of the solute be too high, too low, or unaffected? Explain 192 Molar Mass of a Solid exp15.qxd 9/3/10 6:47 PM Page 193 Experiment 15 Synthesis of Potassium Alum A crystal of potassium alum, KAl(SO4)2•12H2O • To prepare an alum from an aluminum can or foil • To test the purity of the alum using a melting-point measurement Objectives The following techniques are used in the Experimental Procedure: Techniques An alum is a hydrated double sulfate salt with the general formula Introduction MϩMЈ3ϩ (SO4)2 • 12H2O Mϩ is a univalent cation—commonly, Naϩ, Kϩ, Tlϩ, NH4ϩ, or Agϩ; MЈ3ϩ is a trivalent cation—commonly Al3ϩ, Fe3ϩ, Cr3ϩ, Ti3ϩ, or Co3ϩ A common household alum is ammonium aluminum sulfate dodecahydrate (Figure 15.1) Some common alums and their uses are listed in Table 15.1, page 194 Potassium alum, commonly just called alum, is widely used in the chemical industry for home and commercial uses It is extensively used in the pulp and paper industry for sizing paper and for sizing fabrics in the textile industry Alum is also used in municipal water-treatment plants for purifying drinking water In this experiment, potassium aluminum sulfate dodecahydrate (potassium alum), KAl(SO4)2•12H2O, is prepared from an aluminum can or foil and potassium hydroxide Aluminum metal rapidly reacts with a hot, concentrated KOH solution producing a soluble potassium aluminate salt solution and hydrogen gas: Univalent: an ion that has a charge of one Dodeca: Greek prefix meaning “12” Preparation of Potassium Alum Sizing: to effect the porosity of paper or fabrics Al(s) ϩ Kϩ(aq) ϩ OHϪ(aq) ϩ H2O(l) l Kϩ(aq) ϩ Al(OH)4Ϫ(aq) ϩ H2(g) (15.1) When treated with sulfuric acid, the aluminate ion, Al(OH)4Ϫ, precipitates as aluminum hydroxide but redissolves with the application of heat Kϩ(aq) ϩ Al(OH)4Ϫ(aq) ϩ Hϩ(aq) ϩ SO42Ϫ(aq) l Al(OH)3(s) ϩ Kϩ(aq) ϩ SO42Ϫ(aq) ϩ H2O(l) ϩ Al(OH)3(s) ϩ H (aq) ϩ SO4 (aq) ⌬ ¶l Al3ϩ(aq) ϩ SO42Ϫ(aq) ϩ H2O(l) (15.2) 2Ϫ (15.3) Figure 15.1 Ammonium aluminum sulfate dodecahydrate Experiment 15 193 exp15.qxd 9/3/10 6:47 PM Page 194 Table 15.1 Common Alums Alum Formula Uses Sodium aluminum sulfate dodecahydrate (sodium alum) NaAl(SO4)2•12H2O Baking powders: hydrolysis of Al3ϩ releases Hϩ in water to react with the HCO3Ϫ in baking soda—this produces CO2, causing the dough to rise Potassium aluminum sulfate dodecahydrate (alum or potassium alum) KAl(SO4)2•12H2O Water puri cation, sewage treatment, re extinguishers, and sizing paper Ammonium aluminum sulfate dodecahydrate (ammonium alum) NH4Al(SO4)2•12H2O Pickling cucumbers Potassium chromium(III) sulfate dodecahydrate (chrome alum) KCr(SO4)2•12H2O Tanning leather and waterproo ng fabrics Ammonium ferric sulfate dodecahydrate (ferric alum) NH4Fe(SO4)2•12H2O Mordant in dying and printing textiles Potassium aluminum sulfate dodecahydrate forms octahedral-shaped crystals when the nearly saturated solution cools (see opening photo): Kϩ(aq) ϩ Al3ϩ(aq) ϩ SO42Ϫ(aq) ϩ 12 H2O(l) l KAl(SO4)2•12H2O(s) (15.4) Experimental Procedure Procedure Overview: A known mass of starting material is used to synthesize the potassium alum The synthesis requires the careful transfer of solutions and some evaporation and cooling techniques A Potassium Alum Synthesis Prepare an ice bath by half- lling a 600-mL beaker with ice Prepare the aluminum sample Cut an approximate 2-inch square of scrap aluminum (foil or beverage can) and clean both sides (to remove the plastic coating on the inside, a paint covering on the outside) with steel wool or sand paper Rinse the aluminum with deionized water Cut the clean aluminum into small pieces.1 Tare a 100-mL beaker and measure about 0.5 g (Ϯ0.01 g) of aluminum pieces Dissolve the aluminum pieces Move the beaker to a well-ventilated area such as a fume hood Add 10–12 mL of M KOH to the aluminum pieces (Caution: Wear safety glasses; not splatter the solution—KOH is caustic), and swirl the reaction mixture Warm the beaker gently with a cool ame or hot plate to initiate the reaction As the reaction proceeds, hydrogen gas is being evolved as is evidenced by the zzing at the edges of the aluminum pieces The dissolution of the aluminum pieces may take up to 20 minutes; it is important to maintain the solution at a level that is one-half to three-fourths of its original volume by adding small portions of deionized water during the dissolution process.2 Gravity filter the reaction mixture When no further reaction is evident, return the reaction mixture to the laboratory desk Gravity filter the warm reaction mixture through a cotton plug or filter paper into a 100-mL beaker to remove the insoluble impurities (see Figures T.11d and T.11e) If solid particles appear in the filtrate, repeat the filtration Rinse the filter with 2–3 mL of deionized water Cool flame: a nonluminous Bunsen flame with a reduced flow of natural gas The smaller the aluminum pieces, the more rapid is the reaction Some impurities, such as the label or the plastic lining of the can, may remain undissolved 194 Synthesis of Potassium Alum exp15.qxd 9/3/10 6:47 PM Page 195 Allow the formation of aluminum hydroxide Allow the clear solution (the ltrate) to cool in the 100-mL beaker While stirring, use a 10-mL graduated cylinder to slowly add, in 2–3-mL increments (Caution: An exothermic reaction), ϳ10 mL of M H2SO4 (Caution: Avoid skin contact!) Dissolve the aluminum hydroxide When the solution shows evidence of the white, gelatinous Al(OH)3 precipitate in the acidi ed ltrate, stop adding the M H2SO4 Gently heat the mixture until the Al(OH)3 dissolves Crystallize the alum Remove the solution from the heat Cool the solution in an ice bath Alum crystals should form within 20 minutes If crystals not form, use a hot plate (Figure 15.2) to gently reduce the volume by one-third to one-half (do not boil!) and return to the ice bath For larger crystals and a higher yield, allow the crystallization process to continue until the next laboratory period Isolate and wash the alum crystals Vacuum lter the alum crystals from the solution Wash the crystals on the lter paper with two (cooled-to-ice temperature) 5-mL portions of a 50% (by volume) ethanol–water solution.3 Maintain the vacuum suction until the crystals appear dry Determine the mass (Ϯ0.01 g) of the crystals Have your laboratory instructor approve the synthesis of your alum Percent yield Calculate the percent yield of your alum crystals Disposal: Discard the filtrate in the Waste Salts container CLEANUP: Rinse all glassware twice with tap water and twice with deionized water All rinses can be discarded as advised by your instructor, followed by a generous amount of tap water The melting point of the alum sample can be determined with either a commercial melting point apparatus (Figure 15.5, page 196) or with the apparatus shown in Figure 15.6, page 196 Consult with your instructor Prepare the alum in the melting-point tube Place nely ground, dry alum to a depth of about 0.5 cm in the bottom of a melting point capillary tube To this, place some alum on a piece of dry lter paper and “tap–tap” the open end of the capillary tube into the alum until the alum is at a depth of about 0.5 cm (Figure 15.3, page 196) Invert the capillary tube and compact the alum at the bottom of the tube— either drop the tube onto the lab bench through a 25-cm piece of glass tubing (Figure 15.4, page 196) or vibrate the capillary tube with a triangular le (Figure 15.4) Determine the melting point of the alum Use the apparatus in either Figure 15.5 or 15.6 a Melting-point apparatus, Figure 15.5 Place the capillary tube containing the sample into the melting-point apparatus b Melting-point apparatus, Figure 15.6 Mount the capillary tube containing the sample beside the thermometer bulb (Figure 15.6 insert) with a rubber band or tubing Transfer the sample/thermometer into the water bath c Heat the sample Slowly heat the sample at about 3ЊC per minute while carefully watching the alum sample When the solid melts, note the temperature Allow the sample to cool to just below this approximate melting point; at a 1ЊC per minute heating rate, heat again until it melts Repeat the cooling/heating cycle until reproducibility is obtained—this is the melting point of your alum Record this on the Report Sheet The alum crystals are marginally soluble in a 50% (by volume) ethanol–water solution B Melting Point of the Alum Stirring rod Iron ring Reduce volume Gentle heat Figure 15.2 Reduce the volume of the solution on a hot plate Experiment 15 195 exp15.qxd 9/3/10 6:47 PM Page 196 Figure 15.3 Invert the capillary melting point tube into the sample and “tap-tap.” Figure 15.4 Compact the sample to the bottom of the capillary melting-point tube by (a) dropping the capillary tube into a long piece of glass tubing or (b) vibrating the sample with a triangular file Disposal: Dispose of the melting point tube in the Glass Only container The Next Step Other alums (Table 15.1) can be similarly synthesized (1) Design a procedure for synthesizing other alums (2) Research the role of alums in soil chemistry, in the dyeing industry, the leather industry, water purification, or the food industry (3) “Growing” alum crystals can be a very rewarding scientific accomplishment, especially the “big” crystals! How is it done? Figure 15.5 Electrothermal melting-point apparatus 196 Synthesis of Potassium Alum Figure 15.6 Melting-point apparatus for an alum bapp02.qxd 9/1/10 4:46 PM Page 437 Figure B.1a The standard error curve Figure B.1b Error curve for highprecision data values If x1, x2, x3, and so on are measured values, and there are n of them, then the average value, x, is computed as average (or mean) value, x ϭ x1 ϩ x2 ϩ x3 ϩ ϩ xn n (B.1) Most values lie close to the average, but some lie farther away If we plot the frequency with which a measured value occurs versus the value of the measurement, we obtain the curve in Figure B.1a When the random errors are small (high-precision data, Figure B.1b), the curve is very narrow, and the peak is sharp When the random errors are large (low-precision data, Figure B.1c), the data are more spread out, and the error curve is broader and less sharp Figure B.1c Error curve for low-precision data Figure B.2a Relationship of the standard deviation to the error curve Appendix B 437 bapp02.qxd 9/1/10 4:46 PM Page 438 Figure B.2b Data set with a large standard deviation Standard Deviation, s Figure B.2c Data set with a small standard deviation Statistics gives us methods for computing quantities that tell us about the width of the error curve for our data and, therefore, about the precision of the data, even when the amount of data is relatively small One of the most important statistical measures of precision is the standard deviation, s To calculate the standard deviation, we rst compute the average value, x The next step is to compute the deviation, d, from the average value for each measurement—the difference between the average and each measured value: deviation, di ϭ x Ϫ xi (B.2) di is the deviation for the measured value, xi The standard deviation is obtained by squaring the deviations of all measurements, adding the squared values together, dividing this sum by n Ϫ (where n is the number of measurements), and then taking the square root: d 21 d 22 … d 2n standard deviation, s (B.3) (n 1) The standard deviation means that if we make yet another measurement, the probability that its value will lie within Ϯs of the average value is 0.68 In other words, 68 percent of the measurements lie within Ϯs of the average value (i.e., within the range x Ϫ s to x ϩ s) On the error curve in Figure B.2a, page 437, this represents the measurements falling within the shaded area If we obtain a large calculated s from a set of measured values, it means that the error curve for our data is broad and that the precision of the data is low (Figure B.2b); a small value of s for a set of data means that the error curve is narrow, and the precision of the data is high (see Figure B.2c) Thus, s is a statistical measure of the precision of the data For most scienti c data, three results is the absolute minimum number for determining the standard deviation of the data Chemists tend to require four or more results for a meaningful interpretation of the standard deviation value of the data Relative Standard Deviation 438 Treatment of Data The ratio of the standard deviation to the average value of the data often gives a better appreciation for the precision of the data The ratio, called the relative standard deviation (RSD), is either expressed in parts per thousand (ppt) or parts per hundred (pph or percent) bapp02.qxd 9/1/10 4:46 PM Page 439 When expressed as a percentage, the RSD is referred to as %RSD or as the coef cient of variation (CV) of the data RSD ϭ s ϫ 1,000 ppt x s %RSD (or CV) ϭ ϫ 100% x (B.4) (B.5) The RSD or CV expresses precision of the data—the smaller the RSD or CV, the greater the precision for the average value of the data As an example that illustrates how these statistical methods are applied, suppose that four analyses of an iron ore sample give the following data with four signi cant gures: Trial Mass of Iron per kg Ore Sample 39.74 g/kg 40.06 g/kg 39.06 g/kg 40.92 g/kg average (or mean) value, x ϭ 39.74 ϩ 40.06 ϩ 39.06 ϩ 40.92 ϭ 39.94 g/kg To calculate the standard deviation and percent relative standard deviation (or coef cient of variation), compute the deviations and their squares Let’s set up a table Trial Measured Values 39.74 g 40.06 g 39.06 g 40.92 g x ϭ 39.94 g di ϭ x Ϫ xi d 2i 0.20 Ϫ0.12 0.88 Ϫ0.98 0.040 0.014 0.77 0.96 Sum ϭ 1.78 standard deviation, s %RSD (or CV) ϭ 1.78 0.77 0.77 ϫ 100 ϭ 1.93% 39.94 The precision of our analysis is expressed in terms of a standard deviation; the amount of iron in the sample is reported as 39.94 Ϯ 0.77 g Fe/kg of sample, meaning that 68 percent of subsequent analyses should be in the range of 39.94 Ϯ 0.77 g Fe/kg of sample The percent relative standard deviation, %RSD (or coef cient of variation, CV), of the precision of the data is 1.93 percent Scientists check the accuracy of their measurements by comparing their results with values that are well established and considered accepted values Many reference books, such as the Chemical Rubber Company’s (CRC) Handbook of Chemistry and Physics, are used to check a result against an accepted value To report the relative error in your result, take the absolute value of the difference between your measured value and the accepted value and divide this difference by the accepted value Taking x to be your measured value and y to be the accepted value, relative error ϭ ͉x Ϫ y ͉ y Relative Error (B.6) Relative error may be expressed as percent or parts per thousand, multiplying the relative error by 100 or 1,000 Appendix B 439 bapp03.qxd 9/1/10 4:47 PM Page 440 Appendix C Graphing Data Plotted data show how the solubilities of salts vary with temperature A well-designed graph of experimental data is a very effective organization of the data for observing trends, discovering relationships, or predicting information It is therefore worthwhile to learn how to effectively construct and present a graph and how to extract information from it Graph Construction In general, a graph is constructed on a set of perpendicular axes (Figure C.1); the vertical axis (the y axis) is the ordinate, and the horizontal axis (the x axis) is the abscissa Constructing a graph involves the following ve steps whether the graph is constructed manually or with the appropriate software such as Excel torr Select the axes First choose which variable corresponds to the ordinate and which one corresponds to the abscissa Usually, the dependent variable is plotted mL Figure C.1 A graph is usually constructed on a set of perpendicular axes 440 Graphing Data Figure C.2 An example of a properly drawn and labeled graph showing how the pressure of a gas depends on the volume of that gas bapp03.qxd 9/1/10 4:47 PM Page 441 along the ordinate and values of the independent variable along the abscissa For example, if we observe how the pressure of a gas responds to a change in volume, pressure is the dependent variable We therefore assign pressure to the vertical axis and volume to the horizontal axis; we say we are plotting pressure versus volume Be sure to label each axis by indicating the units that correspond to the variables being plotted (Figure C.2) Set the scales for the axes Construct the graph so that the data ll as much of the space of the graph paper as possible Therefore, choose scales for the x- and y-axes that cover the range of the experimental data For example, if the measured pressure range is 150 to 740 torr, choose a pressure scale that ranges from 100 to 800 torr This covers the entire data range and allows us to mark the major divisions at intervals of 100 torr (Figure C.2) When choosing the scale, always choose values for the major divisions that make the smaller subdivisions easy to interpret With major divisions at every 100 torr, minor divisions occur at every 50 torr This makes plotting values such as 525 torr very simple Construct the scale for the x-axis in the same manner In Figure C.2, the volumes range from 170 mL at a pressure of 150 torr to 85 mL at a pressure of 750 torr The scale on the x-axis ranges from 80 to 180 mL and is marked off in 20-mL intervals Label each axis with the appropriate units There are a few additional points to note about marking the scales of a graph: • The values plotted along the axes not have to begin at zero at the origin; in fact, they seldom • The size of the minor subdivisions should permit estimation of all the signi cant gures used in obtaining the data (if pressure measurements are made to the nearest torr, then the pressure scale should be interpreted to read to the nearest torr) • If the graph is used for extrapolation, be sure that the range of scales covers the range of the extrapolation Plot the data Place a dot for each data point at the appropriate place on the graph Draw a small circle around the dot Ideally, the size of the circle should approximate the estimated error in the measurement For most software graphing programs, error bars can be added to the data points to better represent the precision of the data If you plot two or more different data sets on the same graph, use different-shaped symbols (triangle, square, diamond, etc.) around the data points to distinguish one set of data from another Draw a curve for the best t Draw a smooth curve that best ts your data This line does not have to pass through the centers of all the data points, or even through any of them, but it should pass as closely as possible to all of them Most software has the option of adding a trendline to the plotted data Generally, several options as to the type of trendline are offered—select the one that best ts your data Note that the line in Figure C.2 is not drawn through the circles It stops at the edge of the circle, passes undrawn through it, and then emerges from the other side Title your graph Place a descriptive title in the upper portion of the graph, well away from the data points and the smooth curve Include your name and date under the title Often, the graphical relationship between measured quantities produces a straight line This is the case, for example, when we plot pressure versus temperature for a xed volume of gas Such linear relationships are useful because the line corresponding to the best t of the data points can be drawn with a straight edge and because quantitative (extrapolated) information about the relationship is easily obtained directly from the graph Algebraically, a straight line is described by the equation y ϭ mx ϩ b Straight-Line Graphs (C.1) Appendix C 441 9/1/10 4:47 PM Page 442 torr bapp03.qxd K Figure C.3 The slope and intercept for a straight line, y ϭ mx ϩ b Figure C.4 Determination of the slope of a straight line drawn for a plot of pressure versus temperature for a gas m is the slope of the straight line and b is the point of intersection of the line with the y-axis when x ϭ (Figure C.3) The slope of the line, which is usually of greatest interest, is determined from the relationship y2 Ϫ y1 ⌬y mϭx Ϫx ϭ ⌬x (C.2) torr Figure C.4 illustrates the determination of the slope for a typical plot of pressure versus temperature First plot the data and then draw the best straight line Next, choose points on the drawn line corresponding to the easily readable values along the x-axis Read corresponding y values along the y-axis, and then compute the slope Using appropriate software, if a straight line is the selected trendline, the equation for the straight line is generally given, from which the slope and y-intercept can be obtained See Figure C.5 K Figure C.5 Using Microsoft Excel, the equation for the trendline provides the slope and y-intercept for the pressure versus temperature data 442 Graphing Data bapp04.qxd 9/1/10 4:48 PM Page 443 Appendix D Familiar Names of Common Chemicals Sodium bicarbonate is commonly called baking soda or bicarbonate of soda Familiar Name Chemical Name Formula alcohol aqua regia aspirin baking soda banana oil bauxite bleaching powder blue vitriol borax (tincal) brimstone calamine calcite Calgon calomel carborundum caustic soda chalk Chile saltpeter copperas cream of tartar DDT dextrose Epsom salt fool’s gold Freon Glauber’s salt glycerin green vitriol gypsum hypo invert sugar laughing gas levulose lye magnesia marble marsh gas milk of lime (limewater) milk of magnesia milk sugar Mohr’s salt moth balls muriatic acid oil of vitriol ethanol (ethyl alcohol) mixture of conc nitric and hydrochloric acids acetylsalicylic acid sodium bicarbonate amyl acetate hydrated aluminum oxide calcium chloride hypochlorite copper(II) sulfate pentahydrate sodium tetraborate decahydrate sulfur zinc oxide calcium carbonate polymer of sodium metaphosphate mercury(I) chloride silicon carbide sodium hydroxide calcium carbonate sodium nitrate iron(II) sulfate heptahydrate potassium hydrogen tartrate dichlorodiphenyltrichloroethane glucose magnesium sulfate heptahydrate iron pyrite dichlorodi uoromethane sodium sulfate decahydrate glycerol iron(II) sulfate heptahydrate calcium sulfate dihydrate sodium thiosulfate pentahydrate mixture of glucose and fructose nitrous oxide fructose sodium hydroxide magnesium oxide calcium carbonate methane calcium hydroxide magnesium hydroxide lactose iron(II) ammonium sulfate hexahydrate naphthalene hydrochloric acid sulfuric acid C2H5OH HNO3 ϩ HCl by volume CH3COOC6H4COOH NaHCO3 CH3COOC5H11 Al2O3 • xH2O Ca(ClO)2, Ca(ClO)Cl CuSO4 • 5H2O Na2B4O7 • 10H2O S8 ZnO CaCO3 (NaPO3)x Hg2Cl2 SiC NaOH CaCO3 NaNO3 FeSO4 • 7H2O KHC4H4O6 (C6H4Cl)2CHCCl3 C6H12O6 MgSO4 • 7H2O FeS2 CCl2F2 Na2SO4 • 10H2O C3H5(OH)3 FeSO4 • 7H2O CaSO4 • 2H2O Na2S2O3 • 5H2O C6H12O6 ϩ C6H12O6 N 2O C6H12O6 NaOH MgO CaCO3 CH4 Ca(OH)2 Mg(OH)2 C12H22O11 Fe(NH4)2(SO4)2 • 6H2O C10H8 HCl(aq) H2SO4(aq) Appendix D 443 bapp04.qxd 9/1/10 4:48 PM Page 444 Familiar Name Chemical Name Formula oil of wintergreen oleum Paris green plaster of Paris potash quartz quicklime Rochelle salt rouge sal ammoniac salt (table salt) saltpeter silica sugar (table sugar) Te on washing soda white lead wood alcohol methyl salicylate fuming sulfuric acid double salt of copper(II) acetate and copper(II) arsenite calcium sulfate hemihydrate potassium carbonate silicon dioxide calcium oxide potassium sodium tartrate iron(III) oxide ammonium chloride sodium chloride potassium nitrate silicon dioxide sucrose polymer of tetra uoroethylene sodium carbonate decahydrate basic lead carbonate methanol (methyl alcohol) C6H4(OH)COOCH3 H2S2O7 Cu(CH3CO2)2 • Cu3(AsO3)2 CaSO4 • 2H2O K2CO3 SiO2 CaO KNaC4H4O6 Fe2O3 NH4Cl NaCl KNO3 SiO2 C12H22O11 (C2F4)x Na2CO3 • 10H2O PbCO3 • Pb(OH)2 CH3OH For a listing of more common chemical names, go to www.chemistry.about.com and www.sciencecompany.com (patinas for metal artists) 444 Familiar Names of Common Chemicals bapp05.qxd 9/1/10 4:48 PM Page 445 Appendix E Vapor Pressure of Water Vapor pressure of water as a function of temperature Temperature (ЊC) 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 37* — 100 Pressure (Torr) 4.6 6.5 9.2 9.8 10.5 11.2 12.0 12.5 13.6 14.5 15.5 16.5 17.5 18.6 19.8 21.0 22.3 23.8 25.2 26.7 28.3 30.0 31.8 33.7 35.7 37.7 39.9 42.2 47.1 — 760 *Body temperature Appendix E 445 bapp06.qxd 9/1/10 4:49 PM Page 446 Appendix F Concentrations of Acids and Bases Concentrated laboratory acids and bases Approximate Molar Concentration Reagent Acetic acid Hydrochloric acid Nitric acid Phosphoric acid Sulfuric acid Ammonia (aq) (ammonium hydroxide) Potassium hydroxide Sodium hydroxide Approximate Mass Percent Speci c Gravity mL to Dilute to L for a 1.0 M Solution 17.4 (conc) 11.6 (conc) 16.0 (conc) 18.1 (conc) 18.0 (conc) 14.8 (conc) 99.5 36 71 85 96 28%(NH3) 1.05 1.18 1.42 1.70 1.84 0.90 57.5 86.2 62.5 68.0 55.6 67.6 13.5 19.1 50 50 1.52 1.53 74.1 52.4 Caution: When diluting reagents, add the more concentrated reagent to the more dilute reagent (or solvent) Never add water to a concentrated acid! 446 Concentrations of Acids and Bases bapp07.qxd 9/1/10 4:51 PM Page 447 Appendix G Water Solubility of Inorganic Salts Many salts, such as cadmium sulfide, have very low solubilities All salts of the chloride ion (ClϪ), bromide ion (BrϪ), and iodide ion (IϪ) are soluble except those of Agϩ, Hg22ϩ, Pb2ϩ, Cuϩ, and Tlϩ, BiI3, and SnI4 are insoluble PbCl2 is three to ve times more soluble in hot water than in cold water All salts of the acetate ion (CH3CO2Ϫ), nitrate ion (NO3Ϫ), chlorate ion (ClO3Ϫ), perchlorate ion (ClO4Ϫ), and permanganate ion (MnO4Ϫ) are soluble All common salts of the Group 1A cations and ammonium ion (NH4ϩ) are soluble All common salts of the sulfate ion (SO42Ϫ) are soluble except those of Ba2ϩ, Sr2ϩ, Pb2ϩ, and Hg2ϩ All Group 1A and 2A salts of the bicarbonate ion (HCO3Ϫ) are soluble Most salts of the uorosilicate ion (SiF62Ϫ), thiocyanate ion (SCNϪ), and thiosulfate ion (S2O32Ϫ) are soluble Exceptions are the Ba2ϩ and Group 1A uorosilicates, the Agϩ, Hg22ϩ, and Pb2ϩ thiocyanates, and the Agϩ and Pb2ϩ thiosulfates Water-Soluble Salts All common salts of the uoride ion (F Ϫ) are insoluble except those of Agϩ, NH4ϩ, and Group 1A cations In general, all common salts of the carbonate ion (CO32Ϫ), phosphate ion (PO43Ϫ), borate ion (BO33Ϫ), arsenate ion (AsO43Ϫ), arsenite ion (AsO33Ϫ), cyanide ion (CNϪ), ferricyanide ion ([Fe(CN)6]3Ϫ), ferrocyanide ion ([Fe(CN)6]4Ϫ), oxalate ion (C2O42Ϫ), and the sul te ion (SO32Ϫ) are insoluble, except those of NH4ϩ and the Group 1A cations All common salts of the oxide ion (O2Ϫ), and the hydroxide ion (OHϪ) are insoluble except those of the Group 1A cations, Ba2ϩ, Sr2ϩ, and NH4ϩ Ca(OH)2 is slightly soluble Soluble oxides produce the corresponding hydroxides in water All common salts of the sul de ion (S 2Ϫ) are insoluble except those of NH4ϩ and the cations that are isoelectronic with a noble gas (e.g., the Group 1A cations, the Group 2A cations, Al3ϩ, etc.) Most common salts of the chromate ion (CrO42Ϫ) are insoluble except those of NH4ϩ, Ca2ϩ, Cu2ϩ, Mg2ϩ, and the Group 1A cations All common salts of the silicate ion (SiO32Ϫ) are insoluble except those of the Group 1A cations Water-Insoluble Salts Appendix G 447 bapp07.qxd 9/1/10 4:51 PM Page 448 Table G.1 Summary of the Solubility of Salts Anion Soluble Salts with These Cations “Insoluble Salts” with These Cations Acetate, CH3CO2 Arsenate, AsO43Ϫ Arsenite, AsO33Ϫ Borate, BO33Ϫ Bromide, BrϪ Carbonate, CO32Ϫ Chlorate, ClO3Ϫ Chloride, ClϪ Chromate, CrO42Ϫ Cyanide, CNϪ Ferricyanide, [Fe(CN)6]3Ϫ Ferrocyanide, [Fe(CN)6]4Ϫ Fluoride, FϪ Fluorosilicate, SiF62Ϫ Hydroxide, OHϪ Iodide, IϪ Nitrate, NO3Ϫ Nitrite, NO2Ϫ Oxalate, C2O42Ϫ Oxide, O2Ϫ Perchlorate, ClO4Ϫ Permanganate, MnO4Ϫ Phosphate, PO43Ϫ Silicate, SiO32Ϫ Sulfate, SO42Ϫ Sul de, S 2Ϫ Sul te, SO 32Ϫ Thiocyanate, SCNϪ Thiosulfate, S2O32Ϫ Most cations NH4ϩ, Group 1A (except Liϩ) NH4ϩ, Group 1A (except Liϩ) NH4ϩ, Group 1A (except Liϩ) Most cations NH4ϩ, Group 1A (except Liϩ) Most cations Most cations NH4ϩ, Ca2ϩ, Cu2ϩ, Mg2ϩ, Group 1A NH4ϩ, Group 1A (except Liϩ) NH4ϩ, Group 1A (except Liϩ) NH4ϩ, Group 1A (except Liϩ) Agϩ, NH4ϩ, Group 1A Most cations NH4ϩ, Sr2ϩ, Ba2ϩ, Group 1A Most cations Most cations Most cations NH4ϩ, Group 1A (except Liϩ) NH4ϩ, Sr2ϩ, Ba2ϩ, Group 1A Most cations Most cations NH4ϩ, Group 1A (except Liϩ) Group 1A Most cations NH4ϩ, Groups 1A and 2A NH4ϩ, Group 1A (except Liϩ) Most cations Most cations None Most cations Most cations Most cations Agϩ, Hg22ϩ, Pb2ϩ, Cuϩ, Tlϩ Most cations None Agϩ, Hg22ϩ, Pb2ϩ, Cuϩ, Tlϩ Most cations Most cations Most cations Most cations Most cations Ba2ϩ, Group 1A Most cations Agϩ, Hg22ϩ, Pb2ϩ, Cuϩ, Tlϩ, Br3ϩ, Sn4ϩ None None Most cations Most cations None None Most cations Most cations Sr2ϩ, Ba2ϩ, Pb2ϩ, Hg2ϩ Most cations Most cations Agϩ, Hg22ϩ, Pb2ϩ Agϩ, Pb2ϩ Cations Soluble Salts with These Anions “Insoluble Salts” with These Anions Ammonium, NH4ϩ Group 1A Most anions Most anions No common anions No common anions Ϫ 448 Water Solubility of Inorganic Salts This page intentionally left blank InsideCV 8/24/10 8:46 PM Page Name of Chemist Tel No (optional) Local Address (optional) Local Laboratory Information First Term Second Term Third Term Laboratory Instructor’s Name Laboratory Section Number Laboratory Room Number Desk Number Month / Day / Year Location of Safety Equipment Nearest to Your Laboratory Bench Safety Shower Eye Wash Fountain Fire Extinguisher Fume Hood QUICK REFERENCE FOR ICONS USED IN THIS TEXT page 13 page 20 page 26 page 13 page 21 page 26 page 14 page 21 page 27 page 15 page 21 page 27 page 15 page 21 page 28 page 16 page 22 page 29 page 17 page 23 page 30 page 17 page 24 page 32 page 18 page 25 page 32 page 18 page 25 page 19 page 26 InsideBackCV 18 8A 1A H 13 3A 2A Hydrogen 1.00794 14 4A 15 5A 16 6A 17 7A He Helium 4.002602 10 Li Be B C N O F Ne 11 12 13 14 15 16 17 18 Na Mg Al Si P S Cl Ar 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Cd In Sn Sb Te I Xe 95.96 (98) 101.07 102.90550 Palladium 106.42 Ag Lithium 6.941 Sodium Beryllium 9.012182 3B Magnesium 22.989769 24.3050 Potassium 39.0983 Rubidium 85.4678 Calcium 40.078 Strontium 87.62 Scandium 44.955912 Yttrium 88.90585 4B Titanium 47.867 Zirconium 91.224 5B Vanadium 50.9415 Niobium 92.90638 6B Chromium 51.9961 7B 8B Manganese Iron 54.938045 55.845 8B Cobalt 58.933195 Molybdenum Technetium Ruthenium Rhodium 10 8B Nickel 58.6934 11 1B Copper 63.546 Silver 107.8682 12 2B Zinc 65.38 Cadmium 112.411 Carbon 12.0107 Aluminum Silicon 26.9815386 28.0855 Gallium 69.723 Indium 114.818 Nitrogen 14.0067 Phosphorus Sulfur 30.973762 32.065 Germanium Arsenic 72.64 74.92160 Tin 118.710 Oxygen 15.9994 Antimony 121.760 Selenium 78.96 Tellurium 127.60 Fluorine Neon 18.9984032 20.1797 Chlorine 35.453 Bromine 79.904 Iodine 126.90447 Argon 39.948 Krypton 83.798 Xenon 131.293 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Cesium Barium 132.90545 137.327 Boron 10.811 Lanthanum Hafnium 138.90547 178.49 Tantalum Tungsten 180.94788 183.84 Rhenium 186.207 Osmium 190.23 Iridium 192.217 Platinum 195.084 Gold Mercury 196.966569 200.59 Thallium 204.3833 Lead 207.2 Bismuth 208.98040 Polonium (209) Astatine (210) Radon (222) 87 88 89 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Uuq Uup Uuh Uus Uuo (289) (288) (293) (294) (294) Francium (223) Radium (226) Actinium (227) Ruthenfordium (267) Dubnium (268) Seaborgium Bohrium (271) (272) Hassium (270) Meitnerium Darmstadium Roentgenium Copernicium Ununtrium (281) (280) (285) (276) (284) Ununquadium Ununpendium Ununhexium Ununsepium Ununoctium Inner Transition Elements 58 Lanthanide Series Ce Cerium 140.116 Actinide Series 59 60 61 62 63 64 65 66 67 68 69 70 71 Pr Nd Pm Sm Eu Tb Dy Ho Er Tm Yb Lu 140.90765 144.242 (145) 150.36 Europium 151.964 Gd Praseodymium Neodymium Promethium Samarium Gadolinium Terbium 157.25 158.92535 Dysprosium Holmium 162.500 164.93032 Erbium 167.259 Thulium Ytterbium 168.93421 173.054 Lutetium 174.9668 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr (258) (259) (262) Protactinium Uranium Thorium 232.03806 231.03588 238.02891 Neptunium Plutonium (237) (244) Americium Curium (243) (247) Berkelium (247) Californium Einsteinium Fermium (251) (252) (257) Mendelevium Nobelium Lawrencium Page 6:24 PM 1 8/24/10 Periodic Table of the Elements ... shift right, forming the metal–ammonia complex ions:1 [Cu(H2O)4 ]2 (aq) ϩ NH3(aq) [Cu(NH3)4 ]2 (aq) ϩ H2O(l) 2 2 [Ni(H2O)6] (aq) ϩ NH3(aq) [Ni(NH3)6] (aq) ϩ H2O(l) (16 .2) (16.3) Addition of strong... the formula of the complex ion) See Experiment 36 Experimental Procedure 20 4 (repeat of 16.1) The reaction for the formation of colorless N2O4 is exothermic by 58 kJ To favor the formation of N2O4,... experiment, has the formula KAl(SO4 )2 12 H2O; written as a double salt, however, its formula is K2SO4•Al2(SO4)3 24 H2O Refer to Table 15.1 and write the formula of a chrome alum as a double salt