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1: Reaction Stoichiometry

1: Reaction Stoichiometry. Gather all items by the door Find your seat number. Drill 9/4 (A Day) 9/5 (B Day). Outcome: I can use sig figs to correctly measure quantities. Goal: CW 1, CW 2 Hand In: Summer Assignment. CW 1: Safety in the Chemistry Lab. Who has responsibilities for safety?

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1: Reaction Stoichiometry

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  1. 1: Reaction Stoichiometry

  2. Gather all items by the door • Find your seat number Drill9/4 (A Day)9/5 (B Day) Outcome: I can use sig figs to correctly measure quantities. Goal: CW 1, CW 2 Hand In: Summer Assignment

  3. CW 1: Safety in the Chemistry Lab • Who has responsibilities for safety? • The student and the teacher. • What types of clothing are appropriate to wear during a lab? • Goggles, closed toe shoes, no baggy/ loose clothes, no dangling jewelry, tie back hair. • What should you do with backpacks and extra personal belongings during lab? • Put away unnecessary items in backpacks under your desk. Keep walkways clear. • What do you never ever do in a science laboratory? • Eat or drink anything.

  4. CW 1: Safety in the Chemistry Lab • What are the two types of safety equipment? Give an example of each. • Classroom: Eye wash, fire blanket, fire extinguisher, first aid, safety shower. • Personal: Goggles, gloves, apron. • What does this acronym stand for when using a fire extinguisher? • P: Pull the pin • A: Aim at the base of the flame • S: Squeeze the handle • S: Sweep back and forth

  5. CW 1: Safety in the Chemistry Lab • What is the correct way to smell a substance? • Gently waft. • How should you transport chemicals across a classroom? • Walk defensively, elbows in, use both hands. • How should you clean up broken glass? • Use a dust pan and broom. Only pick up glass with safety gloves.

  6. CW 1: Safety in the Chemistry Lab • What should you do if you are unsure of how to proceed during an experiment? • Ask for help. • Why should you not immerse hot glassware into cold water? • It can shatter. • Where should you dispose of chemical wastes? • As directed by your teacher. Do not return unused chemicals to their containers. Do not pour substances down the drain without checking with your teacher. • Where should you point a mouth of a test tube that is being heated? • Away from yourself and others.

  7. Safety Quiz • Complete the safety quiz by bubbling in your scan sheet. • If you finish early, start working individually on CW 2.

  8. CW 2: Measurement and Uncertainty Precision and Accuracy • Accuracy refers to the agreement of a measurement with the true value. Precision refers to the degree of agreement among several measurements of the same quantity. Both relate to error. A random error means that the measurement has an equal probability of too high or too low. This type of error occurs when you estimate the last digit of a measurement. A systematic error occurs in the same direction each time – it is always too high or too low.

  9. CW 2: Measurement and Uncertainty • To check the accuracy of a graduated cylinder, a student measured of water using a buret, placed it into a graduated cylinder, and recorded the volume. • Is this data accurate? Precise? Explain. • Not accurate: the graduated cylinder reads 25 mL, the buret is reading 1 mL high • Precise: all measurements are very close. • What type of error does the data show? Explain. • Systematic error: always too high • Does the student have good measurement technique? Provide evidence. • Yes, the measurements vary at most by 0.09 mL

  10. CW 2: Measurement and Uncertainty Correct Measurement • To correctly measure a quantity, determine what increments the measuring device uses, then measure out to one smaller place. For example, if a ruler goes by 1 cm increments, then your measurement from that ruler should have one decimal place.

  11. CW 2: Measurement and Uncertainty • Measure the following. • Is it possible that each of the three beakers contain the same amount of water? If no, why? If yes, did you report the same values in the previous question? Explain. • Yes, they may all have the same amount of water, but they have different precisions, so that amount may be measured differently. 32 mL 32.7 mL 32.75 mL

  12. CW 2: Measurement and Uncertainty • What graduations (tick marks) would be present on the following graduated cylinders: • one that can measure with a precision of ±0.1 mL. • ±0.1 mL: Goes by 1 (each mark = 1) • one that can measure with a precision of ±0.01 mL. • ±0.01 mL: Goes by 0.1 (each mark = 0.1)

  13. CW 2: Measurement and Uncertainty Rules for Counting Significant Figures • Nonzero integers. Nonzero integers are always significant. • Zeros. There are three classes of zeros: • Leading zeros precede all the nonzero digits. They are placeholders and are not significant. For example, 0.0025 g has two significant figures. • Captive zeros are between nonzero digits. They are significant. For example, 107 g and 1.07 g both have three significant figures. • Trailing zeros are found at the right end of a number. They are only significant if there is a decimal point in the number. For example, 100 g has one significant figure, while 100. g has three significant figures. • Exact numbers. These arise from counted quantities (10 experiments, 28 students) and from definitions, such as conversion factors (1 in = 2.54 cm). • Scientific notation. When written in scientific notation, all digits are significant. For example, 1.2000x108 g has five significant figures.

  14. CW 2: Measurement and Uncertainty • Determine how many significant figures are in the following. • 6.07x10–15 • 0.003840 • 17.00 • 8x108 • 463.8052 • 300 • 301 • 300. 3 SF 4 SF 4 SF 1 SF 7 SF 1 SF 3 SF 3 SF

  15. CW 2: Measurement and Uncertainty • Round off each of the following numbers to the indicated number of significant figures. • 0.00034159 to three sig figs • 103.351x102 to four sig figs • 1.79915 to five sig figs • 3.365x105 to three sig figs • Use scientific notation to express the number 385,500 to • One significant figure • Two significant figures • Three significant figures • Five significant figures 0.000342 103.4x102 1.7992 3.37x105 4x105 3.9x105 3.86x105 3.8550x105

  16. CW 2: Measurement and Uncertainty Addition and Subtraction • The number of significant figures in the answer depends on the least precise place of the measurements.

  17. CW 2: Measurement and Uncertainty Multiplication and Division • The number of significant figures in the answer is the same as the number of significant figures in the least precise measurement.

  18. CW 2: Measurement and Uncertainty Order of Operations • In multistep operations, ensure that you use the correct order of operation (PEMDAS). Mentally keep track of how many significant figures you are left with after each step, but do not round until all steps are complete.

  19. CW 2: Measurement and Uncertainty • Perform the following operations and express each result to the correct number of significant figures. • 188.1 • 12 • 4.89 • 0.22%

  20. CW 2: Measurement and Uncertainty • Perform the following operations and express each result to the correct number of significant figures. 2 SF 3 SF 4 SF 3 SF 1 decimal place, 2 SF

  21. CW 2: Measurement and Uncertainty • Perform the following operations and express each result to the correct number of significant figures. (Assume you are taking the average of 4 numbers, thus 4 is an exact number.) 3 SF (This is a percent error calculation, thus 100 is an exact number.) 2 SF 4 SF

  22. Complete CW 1 and CW 2 • Read Background for LAB 1 Purification of a Mixture • HW 1: Things to Do • Get you syllabus and safety contract signed • Sign up for OWL • Complete OWL tutorial • Sign up for AP Classroom • Bring in lab notebooks Summary9/4 (A Day)9/5 (B Day) Outcome: I can use sig figs to correctly measure quantities. Goal: CW 1, CW 2 Hand In: Summer Assignment

  23. If 3.80 g of H2O are produced, what mass of NaHCO3 reacted? Drill 19/6 (A Day)9/9 (B Day) 2NaHCO3(s) + heat  Na2CO3(s) + CO2(g) + H2O(g) Outcome: I can apply green chemistry principles to the purification of a mixture. Goal: CW 3, Prelab Hand In: syllabus, safety contract,

  24. Lab Guidelines • Write in your lab notebook in pen only. The notebook will make a “carbon” copy of your work. • Use the separation sheet so that the copy is transferred to only one yellow sheet at a time. Press hard enough for the copy to be clear. • Cite any outside of class resources that you use using APA format. • Keep Organized! • Develop a file naming system that makes sense for the word-processed portion of the document and save all files in the same place. • Keep all hand-written work organized in your lab notebook. • You may be able to use these documents to seek additional college credits. • You have a short time to complete the lab. You must work as a team. Does it make sense for 1 person to do the lab while 3 others watch? • Helpful videos can be found here: http://leffellabs.com/ap-videos/

  25. CW 3: Purification of a Mixture Challenge • You have been asked to participate in the peer-review process by an editor of a journal on green chemistry that has received three different manuscripts that report on the same process of separating two substances. You will design a procedure to determine the relative amounts of two substances in a mixture using green chemistry principles, then submit a review on one of the manuscripts to the editor.

  26. CW 3: Purification of a Mixture Pre-Laboratory Work • Introduction: Explain theory and applications behind the lab, as well as any chemical equations, graphs, diagrams, or mathematical equations that will be required. • Discussion of separation techniques for mixtures • Applications (why do we care?) • Green chemistry/ atom economy • Explain how to find the percent NaHCO3 in the mixture

  27. CW 3: Purification of a Mixture Pre-Laboratory Work • Safety Data Sheets: Recreate the table below. Look up the SDS for all chemicals used during the lab and complete the table using the Hazards Identification section. • Materials and Methods: Write a detailed step-by-step procedure for the experiment. Include all the materials, glassware and equipment that will be needed, safety precautions that must be followed, the mass of reactants, accuracy of any equipment, the required data table and calculations.

  28. CW 3: Purification of a Mixture During Laboratory Work • Procedural Notes: Record details of the procedure, exact sizes of glassware, concentrations or amounts of chemicals, instructions for using LoggerPro, and any other notes provided by your instructor or group members. Finalize your procedure. • Data Collection: Create a data table to neatly record measurements, written with the correct precision based on the equipment, detailed observations, and sources of error.

  29. CW 3: Purification of a Mixture Post-Laboratory Work • Calculations: Show one neat handwritten worked example for each major required calculation. Include the unrounded answer and the answers with correct sig figs. • Calculate the % NaHCO3 in the mixture. • Calculate atom economy. • Conclusion: Rather than completing a traditional lab report, you will instead review a lab manuscript on an experiment like the one you carried out and make suggestions for how they may be improved. Each manuscript has some information that is reported well, and some that is reported poorly. As a group, complete one manuscript review, which can be download from LEFFELlabs/ Unit 1.

  30. CW 3: Purification of a Mixture Post-Laboratory Work • Cover Sheet: Create a cover sheet using the exact table below. Place cover sheet on top of items 4 to 7 from above.

  31. CW 3: Purification of a Mixture Guided Inquiry Design and Procedure • In your groups, discuss the following questions, recording your thinking on a sheet of newsprint. • The balanced equation for the experiment is listed below. The desired product is solid metal carbonate. Calculate the atom economy for the reaction. 2KHCO3(s)  K2CO3(s) + H2O(g) + CO2(g) • Review the stoichiometry of the bicarbonate decomposition. How does the mass lost relate to the mass of the starting material? • Some fraction of the starting mass has been lost as H2O(g) and CO2(g). • Equal moles (NOT MASSES!) of H2O(g) and CO2(g) are produced.

  32. CW 3: Purification of a Mixture Guided Inquiry Design and Procedure • In your groups, discuss the following questions, recording your thinking on a sheet of newsprint. • Use your data to determine the percent yield of potassium carbonate. Based on the starting mass of KHCO3 (use stoichiometry)

  33. CW 3: Purification of a Mixture Guided Inquiry Design and Procedure • In your groups, discuss the following questions, recording your thinking on a sheet of newsprint. • Describe how the calculation in Question 3 would change if the sample was a mixture of KHCO3(s) and K2CO3(s)? Keep in mind that K2CO3can decompose further, but only at temperatures above 1200°C, much higher than the Bunsen burner can get. • The mass lost would be equal to the grams of CO2 plus the grams of H2O lost. • What is another possible consideration from the principles of green chemistry that could tell you more about comparing the “greenness” of reactions? • Toxicity of products • A reusable method to speed up the reaction

  34. CW 3: Purification of a Mixture Guided Inquiry Design and Procedure • In your groups, discuss the following questions, recording your thinking on a sheet of newsprint. • What are some reasons the percent yield of a reaction may be less than 100%? • Mass lost due to errors/ poor technique. • What are some reasons percent atom economy may be less than 100%? • Not all the reactants became the desired product, there were by-products.

  35. CW 3: Purification of a Mixture Guided Inquiry Design and Procedure • In your groups, discuss the following questions, recording your thinking on a sheet of newsprint. • Write a detailed step-by-step procedure for the experiment. • Include all the materials, glassware and equipment that will be needed • Safety precautions that must be followed • The mass of reactants to be used • Accuracy of any equipment • Any required data table(s) • Calculations to make • Review additional variables that may affect the reproducibility or accuracy of the experiment and how these variables will be controlled.

  36. Complete pre-laboratory work for LAB 1: Purification of a Mixture. Summary 19/6 (A Day)9/9 (B Day) Outcome: I can apply green chemistry principles to the purification of a mixture. Goal: CW 3 Hand In: syllabus, safety contract, googles

  37. A group of students heated of mixture of NaHCO3 and Na2CO3. Their data is found below. Determine what percentage of the mixture is NaHCO3 and Na2CO3. 2NaHCO3(s)  Na2CO3(s) + H2O(g) + CO2(g) Drill 29/10 (A Day)9/11 (B Day) Outcome: I can apply green chemistry principles to the purification of a mixture. Goal: Complete lab Hand In: Prelab Hint: check your work from last class, Question 4!

  38. Drill Solution 2NaHCO3(s)  Na2CO3(s) + H2O(g) + CO2(g) • A group of students heated of mixture of NaHCO3 and Na2CO3. Their data is found below. Determine what percentage of the mixture is NaHCO3 and Na2CO3. Mass is lost as H2O and CO2 during heating Mole ratio is 1:1 so mol H2O = mol CO2 Let x = mol H2O = mol CO2 Solve for x Convert mol CO2 to g NaHCO3 Find % NaHCO3 in mixture

  39. Summer Assignment Quiz 1 • Clear your desks, you may have a calculator and the reference sheet you picked up by the door. • About 10 minutes.

  40. CW 3: Purification of a Mixture Procedural Notes • You will be given a mixture of NaHCO3(s) and Na2CO3(s). Upon heating, the NaHCO3 will decompose, causing the mass to decrease. Your goal is to use this decrease in mass to calculate the percent of NaHCO3 in the original mixture. • Plan to use about 5 g of the solid mixture. Record exact mass using the analytical balance. • Heat to constant mass: mass the sample, heat, cool, and repeat until the mass stops changing. May take 3 or 4 heating cycles. • Give your crucible a rinse and make sure it’s dry.

  41. Complete CW 3 • HW 2: Stoichiometry I, due 9/12 (A) & 9/13 (B) through OWL • Purification of a Mixture Report Review (one per group), 9/18 (A Day) and 9/19 (B Day) Summary 29/10 (A Day)9/11 (B Day) Outcome: I can apply green chemistry principles to the purification of a mixture. Goal: Complete lab Hand In: Prelab

  42. A molecule containing only nitrogen and oxygen contains 36.8% N (by mass). What is the empirical formula of this compound? Drill 39/12 (A Day)9/13 (B Day) Outcome: I can explain the properties of solutions. Goal: Lab assessment, CW 4

  43. Summer Assignment Quiz 1 • Let’s go over the quiz.

  44. Purification of a Mixture Lab Assessment • Due on the day of the experiment: 1. 2. 3. • Due on the due date (9/19): 4. 5. 6. 7. 8. • Group conclusion • Download Purification of a Mixture Manuscript Review from LEFFELlabs • You will be given a sample lab report (all group members receive a copy) • Work as a group to review to provide a concise report on what is done well and what is lacking. Provide suggestions for the author of the lab report. • Print ONE copy per group.

  45. Purification of a Mixture Lab Assessment • Make sure to read exactly what the problem is asking you – don’t make the question harder than it is. • Just because we used an equation to solve for moles in the lab doesn’t mean you have to do the same thing on the assessment. • Watch your time – go for the low hanging fruit. • Show your work – the AP exam does give partial credit. • Box your final answers and write neatly.

  46. CW 4: Properties of Solutions The Nature of Aqueous Solutions • A solution is a homogenous mixture, made by dissolving a solute in a solvent. There are three types of aqueous solutions, based on how well they conduct electricity. • Strong electrolytes include soluble salts, strong acids, and strong bases. These compounds are completely ionized when added to water. There are seven strong acids to memorize: HCl, HBr, HI, HNO3, HClO4, H2SO4, and HClO3. Strong bases to memorize include group one hydroxides, the most common being NaOH and KOH. • Weak electrolytes exhibit a small amount of ionization when added to water. These include weak acids and weak bases. Nonelectrolytes are substances that dissolve in water, but do not produce any ions. For example, when ethanol dissolves, entire C2H5OH molecules are dispersed in the water.

  47. CW 4: Properties of Solutions • Match each name below with the following microscopic pictures of that compound in aqueous solution. • Barium nitrate • Sodium chloride • Potassium carbonate • Magnesium sulfate MgSO4 K2CO3 Ba(NO3)2 NaCl NO3– Ba(NO3)2 Ba2+ Cl– Na+ NaCl CO3–2 K+ K2CO3 SO42– Mg2+ MgSO4

  48. CW 4: Properties of Solutions • Which picture best represents HNO3(aq)? • HNO3(aq)  H+(aq) + NO3–(aq) • Best matches the NaCl beaker • Why aren’t any of the pictures a good representation of HC2H3O2? • HC2H3O2 is a weak acid: we should see some ionized H+ and C2H3O2– as well as some unionized HC2H3O2

  49. CW 4: Properties of Solutions Molarity • The concentration of a solution is most often expressed as molarity (M), which is defined as moles of solute per volume of solution in liters. When the concentration of a solution is accurately known, either from its preparation or from experimental determination, it is called a standard solution. • To save space in a laboratory, concentrated stock solutions are often prepared. Water is added to achieve the desired molarity, in a process is called dilution. When diluting a solution, remember that the moles of solute before dilution is equal to the moles of solute after dilution. A helpful equation when doing dilutions is below, where M is molarity and V is volume.

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