Chem 150L Cheat Sheet PDF

Fascinating Phenomena Density Measurement Of Liquid 3.1: Acid base Reaction Goal: compare volumetric pipet against graduated cylin...

Fascinating Phenomena Density Measurement Of Liquid 3.1: Acid base Reaction Goal: compare volumetric pipet against graduated cylinder in accuracy (how close data is to true value) Goal: Can you get the dye back to the original color (green)? for density calculations Procedure: Recorded initial concentration of BB, observed color changes with dropwise HCl Procedure: Measure 150 mL beaker mass, use volumetric pipette, graduated cylinder to add 10 mL DI (yellow/orange) and NaOH (blue) to beaker. Measure mass again. Perform 5 determinations each, calculate density. Evaluate accuracy by 3.2: Did you see finding absolute error and assess precision through standard deviation.. Volumetric pipette was winner Goal: Hypothesize reaction products using mass change. - Volumetric pipette more precise (smaller absolute error) → always dispenses the same amount of Procedure: Weighed empty vial, added sodium hydrogen carbonate, observed changes after liquid bc smaller uncertainty 300°C heating, and reweighed post-cooling. - Graduated cylinder → less precise bc larger uncertainty + unequal amount of water dispensed 3.3: Can you grow a seed crystal? (adhesion to sides) Goal: Create supersaturated alum soln & observe crystal growth. - Density calculation: D = Mass/Volume → 0.99609 g/mL = 9.9609g/10mL Procedure: Weighed alum exceeding solubility in beaker, dissolved in DI water, heated & stirred, stored - Absolute error: |true value - measured value| solution for crystal growth observation. Instruments: 10mL volumetric pipette, 10 mL graduated cylinder, top loading balance, 150 mL beaker, Instruments: test tube to hold bromothymol blue, hot plate to heat up NaHCO3, vial to contain analytical balance (water + beaker) NaHCO3, analytical balance to measure the weight of vial+NaHCO3, top loading balance used for alum Post Lab: crystal measurements Post lab: Synthesis of Alum from Aluminum Stoichiometry Goal: What is the yield of this synthesis when you start with 1g of aluminum foil as starting material - Goal: Determine the stoichiometric ratio of elements A and B in a chemical reaction Forming KAl(OH)4: 2Al(s) + 2KOH(aq) + 6H2O(l) → KAl(OH)4 (aq) + 3H2 (g) Procedure: Concentrated solutions A & B were retrieved, and 5 mL of each was transferred into Procedure: Cut aluminum into squares, weighed and placed in beaker.Add KOH, causing volumetric flask, diluted, and mixed. Mixtures w/ A and B in volumes 1:4, 2:3, 2.5:2.5, 3:2, 4:1 prepared bubbling rxn w/ milky white soln. Put beaker in hot water. Set up gravity filtration to in triplicate. Absorbance of each mixture measured using spectrometer. Linear portions on graph were separate solids. Collect filtrate in beaker. identified, and their intersection point indicated stoichiometric ratio Adding 2M KOH to 1g of AL: KOH turned white/translucent, continuous bubbling, ~10mins solution is ofAtoB.MolsofAandBatthispointwere calculated, leading to the formula AyBx and balanced reaction for gray, ~17min reaction slows, exothermic - Forming Alum: KAl(OH)4 (aq) + 2H2SO4 (aq) + 8H2O(l) → A and B. KAl(SO4)2 ・12H2O(l) mole fraction: dividing moles of one component by the total # of moles of all components. - Adding 23 mL 6M H2SO4: white solid formed, after all 23 ml added, solution became white and Job's plots: energy vs mole fraction translucent, after heating at 80oC, solution became clear - Cooling solution in ice bath → clear crystals Tabulate possible compounds of AyBx, appeared in bottom of container (dry using vacuum filtration EX COMPOUND: AB4 Instruments: Top loading balance (weigh Al), reagent-dispensing pump (KOH), graduated cylinder theta = volume of soln A/ volume of A+B = 1/4+1 = 0.2 (H2SO4), vacuum filtration system to (separate liquid and dry alum crystals), stainless steel bowl (ice ————————————————————————————————————————— bath) Neutralization Equivalent Post lab: theoretical yield: look at overall chemical reaction and calculate product in grams using Goal:Accurately determine the concentration of NaOH by titrating it with KHP (Standardize) coefficient ratios Procedure: Burette filled w/ NaOH. Recorded initial weight of burette. KHP weighed w/ weigh paper on - Experimental error: positive (larger than the accepted value), negative (lower than accepted value), analytical balance; added to erlenmeyer flask. DI water added to flask. 3 drops of phenolphthalein added. random (affects each trial differently) Magnetic stir bar dissolved KHP. Titration: NaOH added to flask until soln went from colorless to pink. Synthesis of Alum Continued Final mass burette recorded, & titrations repeated until concentrations matched given concentration. Acid Goal: Continue the synthesis of alum by collecting and drying crystals. base titration eq: HA + OH- --> A- + H2O - as you add base, end up with anion of acid Procedure: Preparing an ice bath to cool the alum mixture, resulting in the formation of white opaque Instruments: 250mL erlenmeyer flask, mass burette, phenolphthalein (indicator), analytical balance crystals at the bottom of the jar and a murky solution. Vacuum filtration used to collect the crystals, (KHP), top loading balance (NaOH) rinsed with water bath. Analysis of Alum Synthesis & Reaction of Calcium Chloride What is the pH of an aq soln of alum? 11.1: Synthesis of Calcium Chloride Goal: pH, raising pH, determining presence of Al ions, sulfate ions, and water Goal: Efficiently synthesize soln of CaCl2 Procedure: A magnetic stir bar placed in beaker with DI - pH of 5% alum solution using pH paper ~ 3.0 water. Calcium metal added, resulting in smoking and opaqueness. HCl gradually added until soln was - Adding drops of 1M KOH → 1: white precipitate formed, 5: white and cloudy solution, 10: clear, 20: clear and precipitate dissolved. Cause temp to go up. Beaker cooled in ice bath. 10.2: Reaction with pink solution (dispose down sink) Alginate - Aluminon turns red when in contact with Al ions → alum solution turned red, sodium sulfate no color Goal: How does introducing sodium alginate into a calcium chloride solution affect the formation and change, aluminum nitrate turned red (4 drops each) - Barium chloride forms properties of the resulting product? Procedure: Sodium alginate added dropwise to calcium chloride in white solid w/ with sulfate ions → alum solution: cloudy solution, sodium sulfate: cloudy solution, beaker using plastic transfer pipette. Gelatinous green solid balls formed. product was examined, aluminum nitrate: no change (“”) revealing non-solid core. The influence of saltwater (sodium hydroxide) on the product was studied: in - Heating to constant weight: 0.3051g to 0.12g, lost mass bc alum is hydrated (KAl(SO4)2 ・12H2O(l)) DI water, alginate balls expanded (lysed), while in sodium hydroxide, alginate balls shrank (crenated). (take mass of sample, heat until no changes, take mass again → repeat until no further changes in mass) Ca(s)+2H2O(l)→Ca(OH)2 (aq)+H2 (g) Ca(OH)2 (aq) + 2HCl (aq) --> CaCl2 (aq) + 2H2O - Crystal: seed crystal suspended in 50mL beaker in saturated solution of alum solution ---------------------------- 5.1: What is the pH of an aq soln of alum? Ca (s) + 2HCl(aq) --> CaCl2 (aq) + H2 (g) Goal: Determine the pH of an aqueous solution of alum and assess if pH measurements can identify Instruments: 100mL graduated cylinder, 250 mL beaker, 50mL beaker, analytical balance, stir plate, compounds. thermometer Procedure: A 5% alum solution was prepared in a beaker, diluted, and its pH tested (pH 3.0) Post Lab:. Comparison with expected pH values indicated similarity to aluminum sulfate. Salicylate Level in a Blood Serum 5.2: What happens when you raise pH of soln? Goal: Determine concentration of salicylate in an unknown serum using standard solutions and a Goal: Investigate the effect of raising the pH on an alum test solution. spectrophotometer. Procedure: Test tubes were filled w/ alum soln. Drops of 1M potassium hydroxide were added to the Procedure: Standard solutions with iron (III) soln and varying salicylate concentrations were prepared solution with dropper, resulting in slight fogging and bubbling. The pH changes were observed through in volumetric flasks. Measured absorbance of each solution at 535 nm after blanking spectrophotometer. 20 dropwise additions. 3 indep. samples from unknown serum prepared similarly, and their absorbance measured. standard 5.3: Does your product contain Al ions? calibration curve used to calculate salicylate concentration in unknown samples Procedure: Test tubes labeled for alum, sodium sulfate, & aluminum nitrate prepared. Aluminon reagent Absorbance ( Y-axis) vs. Concentration (X-axis) added, turning alum solution red, indicating presence of Al ions. 5.4: Does your product contain sulfate ions? CC1 :Dehydration Procedure: Test tubes labeled for alum, sodium sulfate, & aluminum nitrate prepared. Barium chloride Procedure: Weighed empty vial w/ scoop of unknown powder. Put vial on hot plate. Allowed vial to cool reagent reacted, turning alum and sodium sulfate solutions milky&cloudy, confirming the presence of and then reweigh *Summary: finding starting mass of the sample and then find final mass of sample after sulfate ions. heating 5.5: Does your product contain water? CC2: Density Procedure: Alum crystals were heated, producing smoke, bubbling, and liquification. After cooling, Record temp at which density is measured. Measure mass of beaker. Use volumetric pipette to measure successive weighings indicated the removal of water. Dehydrated alum removed from the vial. unknown.Pour measured liquid into beaker and weigh. Calculate density of unknown mass/volume Instruments: Top loading balance to measure mass of alum for pH, analytical balance to test whether C3: NE Equivalent → Titration the alum contains water, pH paper to measure the pH of the alum solution, and hot plate to heat the alum Obtain unknown acid and measure it into an erlenmeyer flask. Add DI water to line on flask. Add 3 drops to a constant weight, test tubes for 5% alum solution of phenolphthalein.Add magnetic stir bar. Record initial weight of burette using toploading balance after Post lab: cancel out each side of equation for net ionic equations filling with NaOH solution.Start titrating by slowly adding NaOH solution from the burette to flask. Solution in flask will turn pink when neutralization point is reached EXCEL Formulas: Model questions: Molarity: mol / Liters What is concentration of hydrochloric acid when a drop of 0.10 M HCl is added to 2.0 mL pure % Mass loss = Mass Difference/ Initial Mass water? Assume 20 drops to 1.0 milliliter. 20 drops = 1 mL so 1 drop = 0.05 mL %w/v = x grams of solute in 100 mL of solvent Total volume = 2.0+0.05 = 2.05 mL= %w/w = mass fraction M1V1 = M2V2 Beer Lambert's Law: relationship b/t concentration of a solute in a soln and amount of light absorbed (0.05mL)(0.10M) = (2.05)M2 by the solution M2 = 0.0024 A = ε*c*l How many sigfigs will stdev usually have? where: 1 significant figure A = absorbance (unitless); ε = molar extinction coefficient (L⋅mol-1cm-1); c= concentration (M); l = Upon heating, if baking soda reacted to give solid sodium carbonate along w/ H2O & CO2 gas that path length (cm) left rxn container, what would be theoretical % mass loss of a sample of baking soda upon heating mole fraction: dividing moles of one component by the total # of moles of all components to a constant weight? Neutralization Eq: amount of an acid or base required to neutralize one eq of the opposite type. 1. Write chemical equation: Neutralization equivalent: mass (g) acid/ (concentrationNaOH * mass(kg) NaOH soln) molar mass * 2NaHCO3 --> Na2CO3 (s) + H2O (g) + CO2 (g) 2. Find total mass of products = 168g (1molHnA/n mol base) molar mass / acidic hydrogens 3. Find % mass loss of baking soda, putting MM of water & carbon dioxide in numerator since they left molar extinction coefficient: measures how much light a substance absorbs at specific wavelength. container Errors: (44 + 18)/168 * 100 Random error: Occurs as a limit of measuring devices, has equal chances of being positive or negative, Use a balanced rxn and concept of limiting reagent to calculate theoretical yield for rxn. and exhibit statistical variation. 1. Write and Balance the Chemical Equation Ex: Different interp. of where meniscus lies 2. Determine limiting reagent by calculating moles of product that can be formed from each reactant. LR Systematic error: occurs as a consistent bias in a system, and it can be detected and corrected produces least amount of product Ex: Scale always measuring 0.300 g over 3. Covert moles of LR to mols of product by using coefficients from balanced equation Error: degree of inaccuracy in a measurement. when measured value deviates from true value. 4. Convert mols of product to grams Error = measured value - true value. Explain how the process of crystallization is necessary to isolate the product, and how this also Top-loading balance vs analytical: If soln has precision of 2 sig figs, top loading sufficient Qualitative leads to the loss of product. Crystallization is vital for purifying a solid product from a solution.By analysis: Figuring out what something is; interrogating qualities of substance. Precision: Refers to how controlling solubility through temperature changes, crystals form and can be separated from close repeated measurements are to eachother soln.Impurities can co-precipitate with crystals, affecting purity. Small amounts of solvent may be Accuracy: refers to how close a measurement is to the correct (true) value retained in the crystals, contributing to lower yield. SDS: Provides information about properties, hazards, and safe use of a chemical product. Describe a synthetic method. Propose to use the method to make a new compound. Synthetic method: series of rxns designed to produce compound from simpler materials. 1. Identify key features/functional groups in Compound X. 2. Break down Compound X into simpler fragments. Identify possible precursors that could lead to the formation of Compound X. 3. Choose appropriate reactions to connect the identified precursors. Example of how to calculate neutralization equivalent using titration data: 1. Find balanced equation 2. Determine Moles of Titrand (acid): 3.Calculate Moles of Titrant 4. Calculate Neutralization Equivalent: Propose structure for product of rxn product of Safety: sodium alginate with calcium chloride. In the event of a fire alarm where do we meet? Peavine Parking Deck The rxn b/t sodium alginate and calcium chloride Where are safety showers? In hallway forms calcium alginate. Flexible backbone and Where are eyewash stations? At each sink -COO-NA+ groups in sodium alginate enable creation of gel-like structure as calcium ions replace What should you do in case of a fire alarm?Turn off gas taps & hotplates. Evacuate sodium ions. Gelation process results in significant transformation, forming beads/long strands, showing cross-linking of alginate polymers w/ calcium chloride. Reversal: high Na+ concentrations, as Na+ ions replace calcium ions, disrupting the gel network. Components of spectrophotometer: Light Source: provides light of specific wavelength. Monochromator: Separates the incoming light into its individual wavelengths. Sample Holder Detector: captures the intensity of light transmitted/reflected by sample. Display: shows the absorbance or transmittance values Transmittance Is ratio of intensity of light transmitted through the sample I to I0. T = I/I0 Absorbance = − log 10 (T) Barium was used to test for presence of sulfate. What observation distinguishes control positive from control negative rxn? Positive: tested a solution known to contain sulfate ions; white precipitate formed. Negative: lack of sulfate ions; no precipitate Precipitate is key to observation to distinguish between control positive and negative What systematic error would occur if the vial were ridiculously short? Positive error. A short vial would cause alum inside to burn since the sides of the vial would get hotter faster. burned alum would cause excess dehydration, leading to lower mass and a error of % loss. Acid Base titration: Determining how much acid is present in sample by observing the precise volume of base that will completely react with an unknown (neutralization equivalent of acid)