CEM Lab Notes PDF

# EXPERIMENT 1 - POST-LABORATORY QUESTIONS 1. A man who is 5 ft. 9 in. tall weighs 170 lb. What is his height in centimeters and his weight in kilograms? * 69 in. x 2.54 cm/1 in. = 175.26 cm * 170 lb x 453.592 g/lb = 77.11 kg 2. Drug medications are often prescribed on the basis of body we...

# EXPERIMENT 1 - POST-LABORATORY QUESTIONS 1. A man who is 5 ft. 9 in. tall weighs 170 lb. What is his height in centimeters and his weight in kilograms? * 69 in. x 2.54 cm/1 in. = 175.26 cm * 170 lb x 453.592 g/lb = 77.11 kg 2. Drug medications are often prescribed on the basis of body weight. The adult dosage of Elixophyllin, a drug used to treat asthma, is 6 mg/kg of body mass. Calculate the dose in milligrams for a 150-lb. person. * 150 lb x 453.592 g/lb = 68.04 kg * 6 mg/kg x 68.04 kg = 1408.24 mg 3. Carry out the following operations and express the answer with the appropriate Number of significant figures and units: * (5.231 mm)(7.1 mm) = 37 mm^2 * (72.3 g/1.21 mL) = 59.8 g/mL * 12.21 g + 0.0132 g = 12.22 g * 31.03 g + 12 mg = 31.04 g 4. A pipet delivers 9.04, 9.02, 9.08, and 9.06 mL in consecutive trials. Find the mean volume and the average deviation from the mean. * Mean = 9.05 mL * Average Deviation = 0.02 mL 5. A 141-mg sample was placed on a watch glass that weighed 9.203 g. What is the weight of the watch glass and sample in grams? * 141 mg x 1 mg/10^-3 g = 0.141 g * Weight of watch glass and sample = 9.203 g + 0.141 g = 9.344 g # EXPERIMENT 4 - POST-LABORATORY QUESTIONS 1. If your percent yield of copper was greater than 100%, what are the two plausible errors you may have made? * Contamination of the product * Incomplete drying of the sample, leading to excess weight. 2. Consider the combustion of methane, CH4: * CH4(g) + 2O2(g) -> CO2(g) + 2H2O(g) * Suppose 1.5 mol of methane is allowed to react with 4 mol of oxygen. * What is the limiting reagent? The limiting reagent is methane (CH4) * How many moles of CO2 can be made from this mixture? How many milligrams of CO2? * Moles of CO2 = 1.5 mol * Mass of CO2 = 1.5 mol x 44.01 g/mol = 66.015 g x 10^-3 g/mg = 66015mg 3. Suppose 8.00 g of CH4 is allowed to burn in the presence of 6.00 g of oxygen. How much (in grams) CH4, O2, CO2, and H2O remain after the reaction is complete? * CH4 = 8.00 g/(16.04 g/mol) = 0.499 mol * O2 = 6.00 g/(32.00 g/mol) = 0.1875 mol * CO2 = 0.1875 mol x 44.01 g/mol = 8.25 g * H2O = 0.1875 mol x 18.02 g/mol = 3.38 g 4. How many milliliters of 6.0 M H2SO4 are required to react with 0.80 g of CuO according to Equation [4]? * Moles of CuO = 0.80 g/(79.55 g/mol) = 0.01006 mol * Volume of 6.0 M H2SO4 = 0.01006 mol/(6.0 mol/L) = 0.001677 L x 10^3 mL/L = 1.68 mL 5. If 2.00 g of Zn is allowed to react with 1.75 g of CuSO4 according to Equation [5], how many moles of Zn will remain after the reaction is complete? * Moles of Zn = 2.00 g/(65.3 g/mol) = 0.0306 mol * Moles of CuSO4 = 1.75 g/(159.61 g/mol) = 0.01096 mol * Remaining Zn = 0.0306 mol - 0.01096 mol = 0.01964 mol 6. What is meant by the term limiting reagent? * The limiting reagent is the reactant that is completely consumed first, limiting the amount of product formed in a reaction. 7. Define molarity. * Molarity is the concentration of a solution expressed as the number of moles of solute per liter of solution (mol/L). # EXPERIMENT 1 - PRE-LABORATORY QUESTIONS 1. What are the basic units of length, mass, volume, and temperature in the SI system? * Length: Meter (m) * Mass: Kilogram (kg) * Volume: Cubic Meter (m^3) * Temperature: Kelvin (K) 2. A liquid has a volume of 3.70 liters. What is its volume in mL? in cm^3? * 3.70 L x 1000 mL/L = 3700 mL * 3.70 L x 1000 cm^3/L = 3700 cm^3 3. If an object weighs 1.47 g, what is its weight in mg? * 1.47 g x 1000 mg/g = 1470 mg 4. Why should you never weigh a hot object? * You should never weigh a hot object because it can cause inaccurate measures. The heat can create air currents that affect a thermometer and volumetric glassware. It could also damage the scale. 5. Why is it necessary to calibrate a thermometer and volumetric glassware? * Calibrating a thermometer and volumetric glassware is important to ensure they give accurate measurements. It helps avoid errors in experiment or calculations. 6. What is precision? * Precision measures how close results are to one another. 7. What is the density of an object with a mass of 1.663 g and a volume of 0.2009 mL? * Density = 1.663 g / 0.2009 mL = 8.28 g/mL 8. Weighing an object three times gave the following results: 9.2 g, 9.1 g, and 9.3 g. Find the mean weight and the standard deviation from the mean. * Mean = (9.2 + 9.1 + 9.3)/3 = 9.2 g * Standard Deviation = √[((9.2 - 9.2)^2 + (9.1 - 9.2)^2 + (9.3 - 9.2)^2)/3] = 0.082 g 9. DNA is approximately 2.5 nm in length. If an average man is 6 ft. tall, how many DNA molecules could be stacked end to end in an average man? * 6 ft x 12 in/ft x 2.54 cm/in x 10 mm/cm x 10^-6 m/mm x 10^9 nm/m = 1.8288 x 10^9 nm * Number of DNA molecules = 1.8288 x 10^9 nm / 2.5 nm/molecule = 7.3152 x 10^8 molecules 10. An object weighs exactly five grams on an analytical balance that has an accuracy of 0.1 mg. To how many significant figures should this weight be recorded? * The weight should be recorded with 4 significant figures to represent the accuracy of the balance. The weight of 5 g can be expressed as 5.000 g. # EXPERIMENT 4 - PRE-LABORATORY QUESTIONS 1. Give an example, other than the ones listed in this experiment, of redox and metathesis reactions. * Redox: The reaction between hydrogen peroxide and potassium permanganate. * Metathesis: The reaction between Silver nitrate and sodium chloride. 2. When will reactions proceed to completion? * Completion occurs when the reactants are fully converted into products, often when one reactant is completely used up. 3. Define percent yield in general terms. * The percent yield is the ratio of the actual yield to the theoretical yield, expressed as a percentage. 4. Name six methods of separating materials. * Filtration * Decantation * evaporation * Distillation * Centrifugation * Chromatography 5. Give criteria in terms of temperature changes for exothermic and endothermic reactions. * Exothermic reactions release heat (temperature increases) while endothermic reactions absorb heat (temperature decreases). 6. What is the maximum percent yield in any reaction? * The maximum percent yield in any reaction is 100%. 7. What is meant by the terms decantation and filtration? * Decantation is pouring off a liquid to separate it from a solid while filtration uses a filter to separate solids from liquids. 8. When Cu(OH)2(s) is heated, copper(II) oxide and water are formed. Write a balanced equation for the reaction. * Cu(OH)2(s) -> CuO(s) + H2O(l) 9. When sulfuric acid and copper (II) oxide are allowed to react, copper (II) sulfate and water are formed. Write a balanced equation for this reaction. * H2SO4(aq) + CuO(s) -> CuSO4(aq) + H2O(l) # EXPERIMENT 1 - POST-LABORATORY QUESTIONS 1. List five physical properties. * Density * Melting Point * Boiling Point * Solubility * State of Matter 2. An 1.192-mL sample of an unknown weighed 9.02 g. What is the density of the unknown? * D = m/V = 9.02 g / 1.192 mL = 7.57 g/mL 3. Are the substances diphenyl and acetone solids or liquids at room temperature? * Diphenyl = Solid * Acetone = Liquid 4. Could you determine the density of cadmium nitrate using water? Why or why not? * No, because cadmium nitrate is soluble in water. When dissolved, it doesn't form a separate phase to measure. 5. What would be the boiling point of acetone at 670 mm Hg? * Acetone's normal boiling point is about 56°C at 760 mm Hg. Since boiling decreases with lower pressure, you can expect the boiling point to be around 50-55°C at 670 mmHg. 6. Why do we calibrate thermometers and pipets? * Calibration helps identify errors from the true values, ensuring accurate measurements and reliability. 7. Is chloroform miscible with water? With cyclohexane? * Chloroform is not miscible with water. It's only slightly soluble. Cyclohexane is miscible. 8. When water and toluene are mixed, two layers form. Is the bottom layer water or toluene? (See Table 2.1) * The bottom layer is water. 9. What solvent would you use to determine the density of cadmium nitrate? * To determine the density of cadmium nitrate, you would use water as a solvent since cadmium nitrate is soluble in water.. 10. The density of a solid with a melting point of 52 to 54°C was determined to be 1.45 ± 0.02 g/mL. What is the solid? * The solid would be benzoic acid. # EXPERIMENT 3 - POST-LABORATORY QUESTIONS 1. Could the separation in this experiment have been done in a different order? For example, if the mixture were first extracted with water and then the extract and the insoluble residue both heated to dryness, could you determine the amounts of NaCl, NH4Cl, and SiO2 originally present? Why or why not? * No, this method wouldn't work because NaCl and NH4Cl are soluble in water, so they would be lost in the extract, impossible to later measure their amounts. SiO2 would remain as residue, but without the others. 2. How could you separate barium sulfate, BaSO4, from NH4Cl ? * Dissolve NH4Cl in water. It's soluble, BaSO4 remains insoluble and can be filtered out. 3. How could you separate barium chloride, BaCl2, from calcium sulfate, CaSO4? * Add water, dissolve BaCl2, filter out undissolved CaSO4. 4. Naphthalene sublimes easily but potassium bromide does not. How could you separate these two substances? * Heat the mixture to sublimate naphthalene. Cool the vapor to collect it as a solid while potassium bromide remains. 5. How could you separate benzophenone from α-naphthol? * You can separate benzophenone from α-naphthol by dissolving the mixture in a suitable solvent and then using fractional crystallization or extraction, as they have different solubilities.