Gen Chem Lab Test – Flashcards
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What are the basic unites of: Length? Mass? Volume? Temperature? in the SI system
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Length = meter Mass = kilogram Volume = m^3 Temperature = kelvin
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What decimal power do the following abbreviations represent? M k m n u
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M = 6 k = 3 m = -3 n = -9 u = -6
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What is the length in millimeters of a crystal of copper sulfate that is 0.180 in. long?
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0.180 in x 1 cm/2.54 in. x 10 mm/1 cm = 4.57 mm
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Perform the following conversions: a) 72.3 mg to g b) 6.0x10^-10 m to mm c) 325 mm to um
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a) 72.3 mg x 1 g/1000 mg = 0.0723 g b) 6.0 x 10^-10 m x 1000 mm/1 m = 6.0 x 10^-7 mm c) 325 mm x 1000 um/1 mm = 3.25 x 10^5 um
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A liquid has a volume of 3.70 L. What is its volume in mL? In cm^3?
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3.70 L x 1000 mL/1 L = 3,700 mL = 3.70 x 10^3 mL 3.70 L x 1000 cm^3/1 L = 3,700 cm^3 = 3.70 x 10^3 cm^3
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Why should you never determine the mass of a hot object?Why should you never place a hot object on the pan of a balance?
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Convection currents tend to buoy the object and thus lead to an inaccurately low mass. Moreover, hot objects can damage the balance. A hot object creates a buoyancy effect by radiating energy in the form of heat and will appear to have a reduced mass. In addition, the hot object may cause damage to the delicate balance and should be allowed to cool to room temperature before its mass is determined.
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Why is it necessary to calibrate a thermometer and volumetric glassware? Why do you calibrate thermometers and pipets?
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Thermometers and volumetric glassware are designed to be accurate. But their manufacture is subject to human error, and they should be calibrated. Thermometers, pipets, and other pieces of laboratory equipment are mass-produced and subject to human error. Consequently, they should be calibrated.
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What is precision?
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Precision is a measure of the internal consistency of a replicate set of data.
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Determining the mass of an object three times gave the following results: 9.2 g, 9.1 g, and 9.3 g. Find the mean mass and the average deviation from the mean.
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9.2 + 9.1 + 9.3 = 27.6/3 = 9.2 (MEAN) |9.2 - 9.2| + |9.1 - 9.2| + |9.3 - 9.2| = 0.2/3 = 0.07 (A.D)
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What is the mass in kilograms of 680 mL of a substance that has a density of 0.930 g/mL?
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D=M/V M=DV M=(680)(0.930) = 632.4 g 632.4 g x 1 g/1000 kg = 0.632 kg
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List 5 physical properties.
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1. Melting Points 2. Boiling Points 3. Solubility Properties 4. Color 5. Densities
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Are the substances lauric acid and stearic acid solids or liquids at room temperature?
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Solids
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Could you determine the density of bromoform using water? Why or why not?
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The density of bromoform could not be determined in water because it is not a solid at room temperature.
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Is toluene miscible with water? With ethyl alcohol?
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Toulon is not miscible with water but is miscible with ethyl alcohol.
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The density of a liquid whose boiling point is 55 degrees to 57 degrees C was determined to be 0.77 +/- 0.05 g/mL. What is the liquid?
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The liquid is acetone assuming that it is the one listed in Table 2.1
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What distinguishes a mixture from an impure substance?
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A mixture differs from an impure substance only in the relative amounts of materials. If the substance contains primarily one component, it is called an impure substance. If, on the other hand, it contains several components in similar amounts, it is called a mixture. In reality, all impure substances are mixtures.
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Define the process of sublimation.
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Sublimation is the process by which a substance changes physical states from the solid state to the gaseous state without passing through the liquid state.
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How do decantation and filtration differ? Which should be faster?
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Filtration differs from decantation in that the liquid phase passes through a semipermeable substance such as a filter paper, whereas in decantation, the liquid phase is separated from the solid phase by carefully pouring off the liquid. Decantation does not involve the use of another substance to achieve the separation and is faster than filtration.
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How does this experiment illustrate the principle of conservation of matter?
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All of the original sample should be recovered; thus, the sum of the masses of the components, NH4Cl, SiO2, and NaCl, should precisely equal the total mass of the sample within experimental error, as no matter is being converted into energy in this experiment.
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How could you separate a mixture of acetone and alpha-naphthol?
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In cyclohexane alpha-naphthol is insoluble and acetone is soluble. Alpha-naphthol can be removed by filtering it from the cyclohexane acetone mixture.
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Percent component
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(mass component in grams x 100%)/(mass sample in grams)
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Before you can write a chemical equation, what must you know?
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Before a chemical equation can be written, you must know the reactants and products of the reaction, their formulas, and their physical states.
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What observations might you make that suggest that a chemical reaction has occurred?
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A color change or formation of a solid or gas is indicative of a chemical reaction, as is evolution or absorption of heat.
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How could you distinguish between NH4Cl and AgCl?
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NH4Cl is soluble in water and AgCl is not.
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Define metathesis reactions. Give an example.
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Metathesis (double replacement) reactions are atom (or group) exchange reactions. For example, AgNO3 (aq) + NaCl (aq) --> AgCl (s) + NaNO3 (aq) is a metathesis reaction in which chloride transfer occurs.
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What is a precipitate?
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A precipitate is an insoluble substance that separates from a homogeneous chemical reaction mixture as a solid.
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Balance these equations: KBrO3 --> KBr + O2 MnBr2 + AgNO3 --> Mn(NO3)2 + AgBr
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2KBrO3 --> 2KBr + 3O2 MnBr2 + 2AgNO3 --> Mn(NO3)2 + 2AgBr
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Give an example, other than the ones listed in this experiment, of redox and metathesis reactions.
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Numerous examples of redox and metathesis reactions could be cited. Two are CuO + H2l --> Cu + H2O (redox) and AgNO3 + NaI --> AgI + NaNO3 (metathesis)
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When will reactions proceed to completion?
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Reactions will proceed to completion whenever one of the products is physically removed from the reaction medium. This often occurs when a gas or solid is formed.
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Define percent yield in general terms.
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Percent yield = (actual yield/theoretical yield)(100%)
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Name six methods of separating materials.
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1. Distillation 2. Sublimation 3. Filtration 4. Decantation 5. Chromatography 6. Extraction
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Give criteria in terms of temperature changes for exothermic and endothermic reactions.
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Exothermic reactions are usually accompanied by a temperature increase, while endothermic reactions are usually accompanied by a temperature decrease.
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If 3.35 g of Cu(NO3)2 are obtained from allowing 2.25 g of Cu to react with excess hno3, what is the percent yield of the reaction?
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The balanced chemical equation is Cu + 4HNO3l --> Cu(NO3)2 + 2H2O + 2NO2. From this equation, moles Cu(NO3)2 = moles Cu and moles Cu = 2.25g/63.55 g/mol = 0.0354 mol The theoretical yield is Cu(NO3)2 = (0.0354 mol)(187.56 g/mol) = 6.66 g % Yield = 3.35 g x100%/6.66 g = 50.3%
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What two liquids are flammable in this experiment?
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Methyl alcohol and acetone
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What is the maximum percent yield in any reaction?
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The maximum percent yield in any reaction is 100%. This occurs when the actual and theoretical yields are the same.
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What is the fundamental difference between gravimetric and volumetric analysis?
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Gravimetric analyses involve a mass measurement as the determining measurement, whereas volumetric analyses involve a volume measurement as the determining measurement.
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What does stoichiometry mean?
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Stoichiometry is the mole or number ration of atoms in a compound or compounds in a chemical reaction and can be related to the amounts (masses) of substances involved in reactions.
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Why should silver chloride be protected from light? Will your result be high or low if you don't protect your silver chloride from light?
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Silver chloride is photosensitive and reacts with light to produce silver metal and chlorine gas, which will lead to a low result if the silver chloride is not protected from light.
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Can you eliminate indeterminate errors from your experiment?
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Indeterminate errors are just that, indeterminate. They cannot be ascertained or eliminated, but rather occur in a random fashion; so they are accounted for with statistics.
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Does standard deviation give a measure of accuracy or precision?
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Standard deviation measures precision
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Why don't you open your folded filter paper so that two pieces touch each side of the funnel?
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If the filter paper were opened this way, the solution and precipitate would simply pass through the opening between the sides of the filter paper and no filtration would result.
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If your silver chloride undergoes extensive photocomposition before you determine its mass will your results be high or low?
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Because photocomposition liberates Cl2 from AgCl according to the equation 2AgCl --> 2Ag + Cl2, the Ag will have a smaller mass than the AgCl and your results will be low.
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Gravimetric Factor
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0.2473; converts grams of AgCl into grams of Cl; used repeatedly in analytical chemistry
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Standard Deviation
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Square root of (the sum of the squares of the average deviations from the mean/number of observations -1) Steps: Find the Mean Find the average deviations Solve the standard deviation
