Lab Final Study Guide PDF

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Talya Kalman Chem 150 Lab Final Notes

Experiment 1 ~ The Fuel in a Lighter I.

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Procedure A. Fill a plastic tub with room temperature water. B. Using a clamp, fully submerge a 50 mL graduated cylinder. 1. Invert C. Weight your lighter D. Discharge the gas using one of two methods 1. Method 1 a) Attach the correct diameter plastic tube to the gas opening on the lighter b) Insert the other end of the tube under the mouth of graduated cylinder, under the water 2. Method 2 a) Hold the lighter directly under the mouth of the cylinder E. When you have dispensed the desired amount of gas, reweigh the lighter F. Adjust the height of the cylinder so that the level of the water inside and outside the cylinder are at the same level 1. Record the volume G. Record the temperature, atmospheric pressure H. Repeat until you feel your data is reliable. Calculations A. Molecular Weight 1. MW = mRT / PV a) MW = apparent molecular weight b) m = mass of sample gas c) P = atmospheric pressure d) T = Kelvin temperature → °celsius + 273.15 e) V = volume of sample f) R= the universal gas constant (1) R=6.24x104 mmHg mL/ mol K 2. Example Trial

Mass Before

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19.5828g

Mass After

Difference of mass

Displacement

Temperature

19.4812g

.1013g

40mL

20.5 C

4

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a) .1013g x (6.24 x 10 mmHg mL / molK) x 293.65 K/ (739.5 mmHg x 40mL) = 62.75g/mol Study Guide Questions A. Pure Water Pressure

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1. If the water pressure is not pure: pressure = pressure water + pressure of gas 2. To find actual molecular weight, you need to make sure you have pure water pressure a) Subtract gas pressure from combined pressure (1) This is going to result in a lower mmHg (pure water) and a higher molecular weight because they are inverse of each other. Whats on the Test: A. Determine the molecular weight of a gas. The gas will be discharged from a cylinder and collected by the water displacement method. 1. MW=mRT/PV a) R=6.24x104 mmHg mL/ mol K B. Techniques 1. Measuring gas volume by water displacement 2. Using a pan balance* 3. Using an analytical balance* C. Chemical Concepts 1. Using the ideal gas law to calculate molecular weight of a gas

Experiment 2 ~ Fascinating Phenomenon I.

Procedure A. Acid-Base Reaction 1. Place a solution of bromothymol blue in a test tube to a depth between 1 and 2 cm. 2. Add 0.1 M HCl dropwise a) Mix the solution after each drop (1) Record observations after each drop b) Stop when there are no further changes 3. Add 0.1 M NaOH a) Dropwise… the same way as the HCl was originally added. 4. Add HCl to get your solution back to the color it was originally 5. Notes: a) Solution starts clear green-blue → HCl turns it yellow → NaOH turns it back to blue b) It takes more drops to get the solution to becomes blue compared to yellow. B. Reaction of Sodium Alginate 1. Synthesize the calcium chloride solution (100 mL of a 0.50 M solution) 2. Place a magnetic stir bar in a 250 mL beaker and add 70 mL of DI water. 3. Weigh out 0.05 moles of calcium metal (2 grams). 4. Add the calcium, slowly, to the stirring water in the 250 mL beaker.

a) Record observations and temperature before and after the calcium is added. 5. Add HCl acid, you want around 0.1 moles and are given that it has 3.0 M (=30 mL) slowly to the stirring mixture. a) Add until the solution clears up and the precipitate has dissolved!! (1) Record observations, temperature, and final volume (HCl). 6. Put the beaker of calcium chloride in a pan of water and continue stirring until room temperature. 7. Obtain 15-20 mL of 1% aqueous solution of sodium alginate in 50 mL beaker. 8. Stop the magnetic stirring and add the alginate solution → add any way you would like to create different shapes and sizes 9. Put half the product into a beaker containing distilled water, and the other half into a beaker containing 1 M sodium chloride C. Phosphate Level: Does a person who drinks Coke have elevated levels of Phosphate? 1. Take a urine sample (5 mL) 2. Use a plastic transfer pipette to transfer 1 mL of urine into a 10 mL graduated cylinder 3. Add 1 mL of the phosphate color reagent. 4. Add some DI water and mix using plastic transfer pipette. 5. Let the solution stand for 10 minutes. 6. Pour the sample from the small graduated cylinder to the large one. 7. Add DI water up to the 25 mL line a) Mix 8. Measure the absorbance of your spectrometer sample at 470 nm II.

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Calculations: A. Moles calcium metal → grams (B) 1. 0.05 mol Ca x (40.078 g / mol) = 2 grams B. Moles of hydrochloric acid → grams (B) 1. 3.0 M = 0.1mol/L → 30 mL Chemicals A. Calcium Metal + Water → Calcium Hydroxide (B) B. Calcium Hydroxide + Hydrochloric Acid → Calcium Chloride (B) C. Sodium Alginate = (C6H7NaO6)n (B) Waste: A. Dispose of the spectrometer samples with the phosphate color reagent into the waste container labeled “Phosphate Test Waste”. (C) B. Rinse all lab equipment that came into contact with specimen with 10% bleach solution provided (C) Study Guide Questions A. Two-step synthesis of aq CaCl from Ca and HCl acid. You can do this by subtracting one from the other.

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1. Step one: Ca(s) +2H2O (aq) -> Ca(OH)2 (aq) +H2(g). 2. Step two: Ca(OH)2 (aq) + 2HCl (aq) -> CaCl2(aq) + 2H2O(aq) 3. Overall: Ca(s) +2HCl(aq) -> CaCl2(aq) +H2(g) B. What are the steps and calculations of getting from the measured absorbance to the concentration of phosphate in your urine. 1. .060A=0.00353x-0.01913 a) x=22.416, multiply this by 25 (because we did 25 mL) b) =560.411ppm. Whats on the Test: A. Given an unknown solution containing phosphate or copper (II) and the correct calibration curve, determine the concentration of the sample. 1. Given equation → A = mx - b a) A is found using absorbance machine b) m and b are given → solve for x (1) Multiply x by number of mL used and find concentration B. Given lithium metal, synthesize lithium chloride as an approximately 0.1 M solution. Use the same method to prepare lithium chloride as you used to prepare calcium chloride. You should plan to make 25 mL of this solution. C. Create a solution of hydrogel formation 1. Procedure B Above D. Techniques 1. Preparing solutions of approximate concentration from a solid* 2. Measuring absorbance using a Genesys 20 or Genesys 30 Spectrophotometer* a) Use DI water to tare it. E. Chemical Concepts 1. Sodium hydroxide is hygroscopic (tending to absorb moisture from the air) and reacts with CO2 (in the atmosphere) 2. Cross-linking of polymers (alginate) produces a change in physical properties.

Experiment 3 ~ Synthesis of Alum from Aluminum I.

Procedure A. Get a piece of aluminum close to the mass you will be using B. Cut it into small square pieces about 4 mm C. Measure and record the mass of your pieces of Al to the nearest 0.01 grams 1. You should be within 0.05g of the target mass. D. Add 30 mL of 2 M KOH to the beaker and observe what happens E. Place a watch glass over the plastic beaker F. When reaction calms down, place the plastic beaker in a 400 mL beaker containing no more than 125 mL of hot water on a hot plate (around 80 °C) 1. Remove plastic beaker from hot bath if the reaction gets too vigorous. G. The reaction is complete when gas evolution ceases or in 20 minutes H. Separate the solids from the liquid by gravity filtration.

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Collect the filtrate in a 250 mL glass beaker 1. Wash filter paper with DI water. 2. Record observations. J. Add 23 mL of 6 M H2SO4 solution in portions to the filtrate. 1. Stir K. When addition is complete, heat the solution to 80 °C with stirring. 1. Turn off the hot plate and allow to cool L. Cool the filtrate in a bowl of ice and water. 1. Swirl a) You should see crystals form M. Collect crystals through vacuum filtration 1. Clamp the filter flask in pace 2. Add circle filter paper 3. Attach the vacuum hose, turn on vacuum, moisten the filter paper, and collect your crystals N. Wash crystals with 10 mL of 50:50 mixture of ethanol and water that is ice-bath cold. O. Wash crystals with two more 10 mL portions of ethanol. P. Dry by pulling air through the filtrate for ten minutes. Q. Transfer dried crystals into a weighed 50 mL beaker. 1. Label it “alum”. Chemicals A. Potassium aluminum sulfate dodecahydrate (alum) = KAl(SO4)2*12H2O B. Potassium Hydroxide= KOH Waste A. Dispose of filter paper in the solid waste container. Study Guide Questions A. WTF Whats on the Test: A. Techniques 1. Determining pH 2. Gravity filtering / Vacuum filtering 3. Heating on a hot plate, and in a water bath* 4. Magnetic stirring* B. Chemical Concepts: 1. Oxidation-Reduction reactions. a) OIL → Oxidation is the gain of oxygen → loss of electrons (+) b) RIG → Reduction is the loss of oxygen → gain of electrons (-)

Experiment 4 ~ Analysis of Alum

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Procedure A. What is the pH of an aqueous solution 1. Prepare 30 mL of an alum solution (5%) a) 1.54 grams alum + 20 mL DI water 2. Measure pH using strips B. What happens when you raise the pH 1. Put some alum test solution in small test tube (1cm) 2. Use KOH to raise pH → mix after each drop 3. Continue until no further changes (20 drops) 4. Results: solution becomes murky white → after 15 drops solution cleared up completely C. Does your product contain aluminum ions? 1. Add alum solution to clean, dry, small test tube 2. Add aluminon 3. Try the same test on the provided solutions of sodium sulfate and aluminum nitrate 4. Results: a) Alum solution + Aluminon = red clear solution b) Aluminum Nitrate + Aluminon = red clear solution c) Sodium Sulfate + Aluminon = lighter red solution D. Does your product contain sulfate ions? 1. Test your alum solution with the barium chloride test solution provided. 2. Try the same test with sodium sulfate and aluminum nitrate. 3. Results: a) Alum Solution + Barium Chloride = white precipitate, murky b) Aluminum Nitrate + Barium Chloride = completely clear, no change c) Sodium Sulfate + Barium Chloride = white precipitate, murky E. Does your product contain water? 1. Set hot plate to medium heat a) Measure temperature (aim for 200-400°C) 2. Weigh 0.2-0.4 grams of crystal into a vial 3. Put vial on hot plate and remove when reaction complete 4. Allow to cool to room temperature and reweigh 5. Repeat until you get two successive matching weights Chemicals A. Sucrose → C12H22O11 Calculations A. To get a concentration of 5% when given mL. → 30 mL x .05= 1.5 mL B. How to find percent mass loss: 1. (Initial Weight - Final Weight / Initial Weight) x 100 = % mass loss Study guide questions A. Raising pH with KOH

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1. Solution became milky but went back to being clear → what occured is similar to why salts do not stay as salts. They can come apart and back together. Similarly, it would stay in a more “milky” state if the solution was not as diluted. B. Testing for sulfate 1. The solution turned white and murky after barium chloride was added, which indicates that there are sulfate ions present in the solution. 2. To prove this, when barium chloride is added to sodium sulfate it is expected to also turn white and murky, which it did. a) This is the positive control 3. When barium chloride is added to aluminum nitrate, there is no change and no white and murky solution because there are no sulfate ions present. a) This is the negative control. C. How to find value and percent error. What’s on the Test: A. Distinguish between samples of: alum, potassium sulfate, aluminum nitrate, barium nitrate, and potassium hydroxide using the same test solutions, apparatuses, and instrument you used in the lab. The samples may be provided as solids or dilute solutions. Describe the observation you use to determine the identity of the compound. If you observe a chemical reaction, write a balanced equation. 1. Aluminum → red 2. Sulfate Ions → white / murky B. You have a hydrate of unknown composition. Heat the sample to a constant weight. As precisely as possible, determine the percent mass loss upon heating and the formula for the hydrate from a list of possible compounds. 1. Procedure E above 2. (Initial Weight - Final Weight / Initial Weight) x 100 = % mass loss C. Techniques 1. Heating to a constant weight 2. Determining pH (using a pH meter and with pH paper)* D. Chemical Concepts: 1. Oxidation reactions (calcium with water, aluminum with KOH) a) Ca(s) + 2H2O(l) ——> Ca(OH)2(aq) + H2(g) b) Al(s) + 2 KOH(aq) + 6 H2O(l) →2 KAl(OH)4 (aq) + 3 H2 (g) 2. "Double Displacement" (or metathesis) reaction (calcium hydroxide with HCl, sulfate with barium) a) Ca(OH)2+ 2HCl → CaCl2+H2O b) Ba + SO4 → BaSO4 3. Acid - Base reactions (alum with KOH, calcium hydroxide with HCl) a) KAl(SO4)2*12H2O(aq) + 3KOH(aq) ⟶ Al(OH)3(s) + 2K2SO4(aq) + 12H2O(l) b) Ca(OH)2(aq) + 2HCl(aq) → CaCl2(aq) + 2H2O(l)

4. Dehydration of inorganic hydrates (alum losing waters of hydration) 5. Amphoteric (of a compound, especially a metal oxide or hydroxide; able to react both as a base and as an acid) reactions of aluminum (III)

Experiment 5 ~ Coke Density I.

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Procedure A. Density of a Liquid: calculate the density of DI water at room temperature using two methods. 1. Method 1: using a volumetric pipette a) Mease the mass of a 150 mL beaker using an analytical balance. b) Use the volumetric pipette to add a 10 mL portion of DI water. c) Measure the mass of the beaker and water (1) Calculate the mass difference (a) Use this to calculate density d) Perform 3 or more replicates 2. Method 2: using a 10 mL graduated cylinder a) Weigh the empty cylinder b) Add water (between 9 and 10 mL) (1) Reweigh c) Make 3 or more replicate density determinations. Calculations A. Calculating Density 1. Density = mass / volume 2. Mass = (Mass of Beaker + Water) - (Mass of Beaker) 3. Volume → using a volumetric pipette, volume always equals 10, using a graduated cylinder volume is somewhere between 9 and 10 B. Using a t-Test 1. Statistical test is used to determine whether the averages from two sets of data are the same or whether the means are different 2. Use a t-Test calculator to find the t and p value 3. Results: a) The absolute value of the calculated t is smaller than critical value (x.xxxy.yyy), so the means are significantly different → conclude that you can use this density measurement to distinguish between the products Notes

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A. Absolute error is the absolute value of the differences between the reference value and the average of your density measurement. B. Percent error is that same difference divided by the reference value and converted to percent. C. Standard deviation is a measure of the spread of the data. 1. Round the standard deviation to the same significant figures as the density. D. To find relative error, divide the Absolute Error by the Actual Value of the item in question to get Relative Error. Whats on the test: A. Prepare a salt solution at a requested concentration and measure the density of the solution. 1. Density = mass / volume B. Two types of measuring devices are available. Determine which one gives the most precise results. Given a reference sample of known value, determine which device give the most accurate results. You may use your laptop computer to calculate averages and standard deviations. 1. Volumetric Pipette vs. Graduated Cylinder 2. Use standard deviation and t-test C. Understand how a t-test can determine if two data sets are different. 1. The absolute value of the calculated t is smaller than critical value (x.xxxy.yyy), so the means are significantly different D. Given a measured and a "true" value, calculate error and percent error. 1. Absolute error is the absolute value of the differences between the reference value and the average of your density measurement. 2. Percent error is that same difference divided by the reference value and converted to percent. E. Techniques 1. Reading a graduated device (cylinder at the bottom of the meniscus, for example)* F. Techniques 1. Practicing The Pipette Rule* 2. Using a volumetric pipette* 3. Determining the density of a liquid G. Chemical Concepts 1. Determining accuracy and precision of a measurement a) Accuracy = how close your calculated number is to the true value b) Precision = how close your calculated numbers are to eachother 2. Determine error in a measurement 3. State random uncertainty as a range 4. Recognize systematic and random error

a) Systematic error- A systematic error is one that results from a persistent issue and leads to a consistent error in your measurements. (1) Example: if your measuring tape has been stretched out, your results will always be lower than the true value b) Random error- errors that fluctuate due to the unpredictability or uncertainty inherent in your measuring process, or the variation in the quantity you’re trying to measure. (1) Example: a spring balance might show some variation in measurement due to fluctuations in temperature. 5. Analyze results of a t test to compare the means of two groups

Experiment 6 ~ Stoichiometry I.

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Procedure A. Prepare Solution A and Solution B 1. Dilute the solutions by a factor of 10 a) Take about 15 mL of a concentrated solution in your smallest beaker b) Using a 5 mL volumetric pipette, transfer precisely 5 mL of the stock solution into your 50 mL labeled volumetric flask c) Add solvent up to the line d) Invert 10 times to make homogenous solution B. React Solution A with Solution B 1. Each sample should contain 5 mL a) Add both solutions in assigned ratio to test tube b) Cover the mouth of the test tube with plastic and invert to create homogenous solution c) Allow reaction to proceed for 10 minutes d) Decide wavelength at which your group will measure absorbance e) Create a graph and look for linear points on right and left (1) Keep testing ratio until you are confident with your results C. Make your absorbance measurements 1. Chose a wavelength that must be held constant by looking at the color AB compound formed (chose wavelength complementary to the color). a) Scale from 400-700… violet→ red 2. Black or zero the spectrometer with DI water before testing for absorbance with your sample. 3. Measure and record the absorbance data for all samples. Notes A. Jobs plott is used to determine the stoichiometry of a binding event.

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1. The spot where the two lines meet is called the stoichiometric point. At this point, the reactants are supplied in the correct ratio to totally consume both of them, leaving nothing in excess. B. Mole fraction is calculated by dividing the moles of one compound by the total number of moles of all the components. C. Volume Fraction is defined as θ = volume A / total volume. D. When you take a measurement of a colored solution it is the wavelength of the absorbed light that is of interest to chemists because it provides clues about molecular structure. E. Beer-Lamber Law: A= Elc 1. A = absorbance 2. E = molar extinction 3. L = distance light travelled through sample (cm) 4. C = concentration Whats on the test? A. Given a standard solution of known concentration, as accurately as possible prepare a 1:10 dilution and a 1:100 solution. Measure the absorbance of the two solutions you prepare. Plot absorbance vs concentration. Determine the extinction coefficient of the solute B. Use a Job's plot to determine the stoichiometry of a reaction. 1. Finding concentration C. Techniques 1. Preparing solutions of approximate concentration by dilution* 2. Using a volumetric pipette* 3. Using a graduated pipette* D. Chemical Concepts 1. Beer-Lambert Law a) that absorbance of a material sample is directly proportional to its thickness. 2. Using the method of continuous variation (Job's plot) to determine stoichiometry. 3. Apply stoichiometry concepts to understand laboratory data.

Experiment 7 ~ Neutralization Equivalent I.

Procedure A. Prepare a solution of NaOH 1. Weigh 2 g...