Unit 8 Homework and Lab Packet

Transcription

1 Name: Per: Unit 8 Homework and Lab Packet!" #$ % % %% ## & '(& ) &"(* ' +", +-.,"/

2 Overall Objective: Understand and apply the properties of water and how they relate to solutions. Iowa Model Core standards addressed: o Understand and applies knowledge of the structure of atoms o Understands and applies knowledge of the structure and properties of matter o Designs and conducts scientific investigations o Uses technology and mathematics to improve investigations and communications Key Concepts: 1. Understand and describe the basic properties of water and ice and how they effect the world around you. 2. Explain the high surface tension and low vapor pressure of water in terms of the structure of the water molecule and hydrogen bonding (15.1.1) 3. Distinguish between solvent and solute (15.2.1) 4. Describe what happens in the solution process (15.2.2) 5. Explain why all ionic compounds are electrolytes (15.2.3) 6. Distinguish between suspension and solution (15.3.2) 7. Identify the distinguishing characteristic of a colloid (15.3.2) 8. Identify the factors that determine the rate at which a solute dissolves (16.1.1) 9. Identify the units usually used to express the solubility of a solute (16.1.2) 10. Identify the factors that determine the mass of solute that will dissolve in a given mass of solute (16.1.3) 11. Solve problems involving the Molarity of a solution (16.2.1) 12. Describe the effect of dilution on the total moles of solute in solution (16.2.2) 13. Define percent by volume and percent by mass solutions (16.2.3) 2

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5 Solvent Suspension Colloid Unsaturated solution Miscible Mayonnaise Blood Jell-o Water and ethanol Salt marshmallow Solute Saturated solution Immiscible Concentration Kool-aid Espresso Tea Oil and water Sugar Water paint Write your lists with a title here 5

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17 STATION Name of Substance FORMULA FORMULA WEIGHT (F.W.) MOLARITY M 1 Sodium thiosulfate L pentahydrate 2 Potassium chlorate cm 3 3 Ammonium chloride cm 3 4 Calcium hydroxide ml 5 Zinc sulfate L heptahydrate 6 Potassium chloride L Hoffman Gen. Chem Solutions 2010 SOLUTION INFORMATION VOLUME OF GRAMS OF SOLUTE SOLUTION 7 Iron(II) sulfate cm 3 heptahydrate 8 Calcium carbonate g 9 Sodium bicarbonate L 10 Copper (II) sulfate L 15 g pentahydrate 11 Calcium chloride 175 cm g 12 Lithium carbonate g Solution Preparation Practice 1) Move around the lab and collect formula weight and formula information from each sample. This is found on the bottle. 2) Move back to your desk with your lab partner and complete the blank spaces under Solution Information 3) Listen to your teacher and take notes on the next page on how to prepare one of the solutions. 17

18 Calculations for Solution Preparation Practice How to prepare a solution. Take notes using text and/or drawings. 18

19 Purpose Directions 1. To practice mixing a Molar solution 2. To mathematically determine the molar (M) concentration of a solution. 3. To quantitatively determine the mass of a solid in solution- in the lab. 1. Go to your lab station- read the information sheet at the station and, working with the pair across from you, calculate how much solute you need to make the desired volume and molarity of the solution. Write down your plan. 2. Go across the room and confirm the calculations of the station next to yours. If incorrect, challenge that group, and correct the calculations if necessary. 3. Return to your station and prepare your solution. 4. When all 6 stations have prepared their solutions- dump your solution into the large common flask. 5. Answer the following questions about the common solution. a. By calculation, what is the Molar concentration (M) of the common solution? Show your work. b. Calculate how many grams of salt would be in 5 ml of the common solution. Show your work. 6. Withdraw 5 ml of the common solution and experimentally determine how many grams of salt is in the solution. (If you need special equipment ask your teacher.) 7. Compare your experimental results with your calculate results in step 5a by doing a percent error. (Actual/theoretical)x100 Conclusion Summarize what you have learned from this lab experience. Describe the salt recovery technique that you used. How efficient was it? What are two sources of error? 19

20 STATION 1 Volume: 125 ml M: 0.15 Mass needed g STATION 4 Volume 110 ml M: 0.75 Mass needed g STATION 2 Volume: 210 ml M: 2.1 Mass needed g STATION 5 Volume: 140 ml M: 1.7 Mass needed g COMMON SOLUTION STATION 3 Volume: 75 ml M: 0.30 Mass needed g STATION 6 Volume: 180 ml M: 1.1 Mass needed g 20

21 Introduction The Kool-Aid that you make when you follow the directions on the back of the package has a 2.0M dye concentration. In this lab we are going to determine if Kool-Aid Jammers that you buy at the store have the same dye concentration. If not we want to determine the concentration (molarity) of the Kool-Aid Jammers. We will start by making up four different concentrations of Kool-Aid( 2M, 1M, 0.5M, 0.25M). We will then use a colorimeter to analyze the samples and measure how much light is absorbed by the solution. The absorbance values will then be recorded and plotted on a graph versus the dye concentration to produce a standard curve. Using this standard curve and the absorbance value of the Kool-Aid Jammer, you can determine the Jammer s dye concentration. Procedure Preparing the Kool-Aid Stock Solution (2.0M) 1. Measure out the amount of Kool-Aid powder you calculated in the first pre-lab questions and place it in a 250mL beaker. 2. Put about 25-50mL of tap water in the beaker and dissolve the powder by mixing with a glass stirring rod. Carefully pour this solution into a 100mL graduated cylinder. 3. Fill the graduated cylinder up to the 100mL line with water from the squirt bottle. 4. Pour the solution back into the beaker. Stir to make sure the Kool-Aid is completely dissolved. 5. Pour a sample of the 2.0M Kool-Aid into a clean test tube and place it in your test tube rack. Preparing the Diluted Kool-Aid Solutions (1.0M, 0.5M, 0.25M) 6. Now you will make three dilutions from this stock solution. a. Use the calculations from pre-lab question #2 to determine how much of the 2.0M Kool- Aid to add to make a 10mL solution of 1.0M Kool-Aid. b. Add the correct amount of 2.0M Kool-Aid to a 10mL graduated cylinder. Use a medicine dropper to help you get the exact amount. c. Fill the graduated cylinder up to the 10mL line using the squirt bottle of water. d. Pour this sample into a clean test tube and place it in your test tube rack. Remember the concentration of this sample. 7. Repeat steps a-d to make the 0.5M and 0.25M Kool-Aid samples. Collecting Absorbance Data from the Colorimeter Your colorimeter is already calibrated and ready to use. 8. Be sure the knob on the colorimeter is turned to Blue (470nm). If it is not, turn the knob now. 9. Fill an empty cuvette ¾ full with the 2.0M Kool-Aid sample. 10. Place this sample into the colorimeter so the clear sides line up with the white line. Close the door and record the absorbance value on the screen in your data table. 11. Clean out the cuvette with distilled water and place the next sample (1.0M Kool-Aid) into the cuvette (or an extra if provided). Place this in the colorimeter and record the absorbance value. Repeat with the 0.5M and 0.25M Kool-Aid solutions. 12. Finally fill the cuvette with the Kool-Aid Jammer sample and record the absorbance value. Clean all your glassware and put your materials back. 21

22 Pre Lab Questions (go in lab notebook) Purpose Statement: Pre-Lab Questions: 1. We need to make 100mL of a 2M Kool-Aid Solution. Remember: Moles of solute Molarity = liters of total solution If Kool-Aid powder has a molar mass of 1 mol=40 g, calculate the amount in grams of powder needed. 2. Then we want to make a 10mL sample of 1M Kool-Aid solution from the 2M stock Kool-aid solution. Use the formula M1V1=M2V2 to determine how much (volume in milliliters) of the 2M Kool-Aid you need to add. 3. Use a similar calculation to #2 to determine how much to make a 10mL sample of 0.5M from the 2.0M stock solution of Kool-Aid. How much (volume in milliliters) of the 2.0M Kool- Aid do you need? 4. Let s do the calculation one more time. Make a 0.25M Kool-Aid solution using the 2.0M stock solution of Kool-Aid. How much (volume in milliters) of the stock solution do you need? Hypothesis: Do you think the concentration of the Kool-Aid Jammer will be greater than, equal to or less than the concentration of Kool-Aid you make at home? Data Table: Create a data table to record all of the measurements you will make in the lab. 22

23 Post-Lab Data Analysis: 1. Graph the absorbance versus Concentration of the samples. Then draw a best fit line. This is your standard curve. 2. Place a circle of * on your standard curve that matches the absorbance value of the Kool-Aid Jammer. Based on your standard curve, what is the dye concentration of the Kool-Aid Jammer sample? Show your work on your graph. 3. What does the absorbance of a solution tell you about the solution? 4. Did the absorbance increase or decrease as the concentration got smaller? Why? Conclusion: 1. Compare the dye concentration of the Kool-aid jammer to the actual concentration that Kool-Aid should be (based on how we are supposed to make it from the package). 2. If your concentrations were similar, explain why the Kool-Aid company would make the dye concentrations the same. OR If your concentrations were different, explain some possible reasons the Kool-Aid company would have a difference in the dye concentration of the Jammer and the solution concentration made from the package. 23

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27 Hoffman Gen. Chem Solutions 2010 That was a Killer Cup of Coffee: Using colorimetry to determine concentration of a poison Determine the concentration of cyanide in the solution A Killer Cup of Coffee? GlobalTech Manager Dies SOUTH PAINTER, Tuesday: It was a normal Morning at GlobalTech Industries until the mail boy discovered project manager Patrick Marchand dead in his cubicle, head on his desk. Mr. Marchand had died while writing an , in a room full of people hard at work. An early examination of the crime scene yielded no clues. Mr. Marchand was known to have a serious heart condition, and many signs pointed to cardiac arrest as the cause of his death. However, as police canvassed the office space, the distinct odor of bitter almonds was detected, and a vial containing a small amount of an unknown chemical was found discarded in a communal trash can. Based on the bitter almond odor, police have tentatively identified the substance as cyanide. The existence of this possible poison has lead police to suspect foul play in Mr. Marchand s death. The police have no leads. LAB NOTES Technician: Beverly Chin -received vile containing 20 ml cyanide solutionconcentration unknown -reacted syanide (CN-) solution with potassium polysulfide (K2Sx) to produce potassium thicyanate (KSCN) -reacted KSCN solution with iron(iii)chloride (FeCl3) to produce iron(iii)thiocyanate ion (FeSCN2+) -determination of amount of FeSCN2+ in reacted solution will allow estimation of concentration of CN- in original solution -included in package: FeSCN2+ solution of unknown concentration 27

28 That was a Killer Cup of Coffee: Using colorimetry to determine concentration of a poison Forensics Objective Use Beer s Law to determine the concentration of Iron (III) thiocyanate (FeSCN 2+ ) in an unknown solution. Science and Mathematics Objectives Use colorimetry to determine the concentration of a colored species in a solution Use a linear relationship to model Beer s Law Materials (for each group) Vernier colorimeter 2 cuvettes Distilled water 50 ml of prepared FeSCN 2+ solution of known concentration 5 ml of FeSCN 2+ solution with unknown concentration GOGGLES Introduction: The colorimeter you will use today is a computer-interfaced probe designed to determine the concentration of a solution by analyzing its color intensity. Light will be absorbed by the solution. This is called absorbance. In general, absorbance is important because of its direct relationship with concentration according to Beer s Law. You will make a graph of absorbance versus concentration of several different samples of known concentration. Then you will find the absorbance of an unknown solution, and, using the graph, determine its concentration. Procedure Part 1: Preparing the solutions Goggles MUST be worn at all times during this lab activity! CAUTION: Be careful not to ingest any solutions or spill any on your skin. Inform your teacher immediately in the event of an accident. A fatal dose of FeSCN 2+ is about 1.5 oz (equivalent to about three of four coffee creamers) or 0.105M 1. The five standard solutions, and the unknown have already been prepare for colorimetry. 28

29 REMEMBER: - Cuvettes fill up FAST. Be careful not to spill. Use 1.5 pipettes to fill each cuvette. - Use two cuvettes for this lab. One with water for a blank and one for your standard solutions. Rinse standard cuvette with the next solution two or three times before filling it and putting it in the colorimeter - Handle a cuvette only by the edges or the ribbed sides. - All solutions should be free of bubbles. Lightly tap the cuvette on the table to move bubbles out of the solution Solution Concentrations Test Tube FeSCN 2+ Solution (ml) Distilled H 2 O (ml) Final Concentration of FeSCN 2+ (mol/l) Part II: Collecting the Data 1. The colorimeter is attached to the computer and the program is open. 2. Calibrate the Colorimeter (may be completed, check with your teacher) a. Click Experiment at the top of the screen and choose Calibrate towards to bottom and choose the colorimeter. b. Place an empty cuvette in the cuvette slot of the Colorimeter. Make sure that one of the transparent faces of the cuvette is pointing toward the white reference mark (match the line on the top of the cuvette with the white line on the colorimeter). Close the lid of the Colorimeter. c. Turn the knob to 0% T. When the voltage value shown on the computer monitor stabilizes, type 0 where it asks you to enter a value. Click Keep. d. Set the wavelength of the Colorimeter to 470 nanometers (nm). This will set the Colorimeter s light emitter and receiver to emit and record blue light. e. Place a cuvette filled ¾ full with distilled water into the colorimeter. f. When the voltage value shown stabilizes, enter 100 for the value. Click Keep. 3. You are now ready to collect absorbance data for the five standard solutions. a. Rinse a cuvette two ro three times with the 0.15M solution. b. Fill a cuvette ¾ full (1.5 pipettes) with solution 0.15M. Place a lid on the cuvette. c. Place the cuvette into the colorimeter. Be sure the ribbed edges face you and away from you. d. Select Collect to begin collecting data. 29

30 e. When the value displayed on the calculator screen has stabilized, select keep to record the absorbance of the first standard. DO NOT CLICK STOP. f. The program will ask you to enter a value. Enter the concentration of FeSCN 2+ in the solution (from the table above). Select OK to store this absorbance-concentration data pair. g. Write the absorbance value, rounded to the nearest 0.001, for each standard solution in your Evidence Record. h. Repeat steps 3a-3g for each of the remaining standards (0.12, 0.09, 0.06 and 0.03) Be sure to enter the correct concentration for each standard in step 3d. 4. Select STOP when you have finished collecting data for all the standards. 5. Logger Pro should display a graph showing concentration of FeSCN 2+ on the x-axis and absorbance of blue light on the y-axis. 6. Rinse the cuvette two or three times with the unknown solution. Fill the cuvette ¾ full with the unknown solution. Place the cuvette with the unknown solution in the Colorimeter. Monitor the absorbance value displayed on the screen. When this value has stabilized, round it to the nearest and write it in your Evidence Record. Note: There s no need to click collect or keep for the unknown. 7. Discard the remaining solutions according to your teacher. Part III: Analyzing the Data 8. To determine the concentration of FeSCN 2+ in the unknown solution, you will use the graph of absorbance vs. concentration for your standard solutions and fit a straight line to the points. Then use the absorbance value of the unknown to estimate its concentration of FeSCN Click the box in the tool bar that says R= in it. It s to the left of the LabPro box. a. This will put a linear fit line through your data and display a box to the right of your graph. b. The equation for the straight line is y=mx+b, where y is absorbance, x is concentration, m is the slope, and b is the y-intercept. The correlation coefficient, R, indicates how well the data points match the line. A value of 1.00 indicates a perfect fit. c. Record the values of m, b, and r in the Evidence Record. 10. The linear relationship (straight line) between absorbance and concentration is known as Beer s Law. 11. Move the mouse along the straight line that was drawn. The values are at the bottom in this format (x, y). Move the mouse along the line until the Y value reads the absorbance of the unknown that you recorded. BE SURE THE CURSOR IS ON THE LINE. a. The corresponding X value is the estimated concentration of FeSCN 2+ in the unknown solution. Write this value in the Evidence Record. %*(&(+, (#(- 30

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