CHEM 1411 Practice Lab Exam: Total 100 points. Separation of the Components in an Inorganic Mixture Mass of evaporating dish: 42.8 g Mass of evaporating dish and unknown mixture: 45.6 g Mass of unknown mixture: _________2.8_____ g Mass of evaporating dish after subliming NH4Cl: 44.6 g Mass of NH4Cl: ___1.0____________ g Percent of NH4Cl: _____35.71________ % (Show calculations for percent of NH4Cl) (1.0/2.8)x100% What does MSDS mean? This is to ask you to write out the whole words of this abbreviation. Material Safety Data Sheet Why you must do the first heating in the fume hood? The white fume has odor and irritant to lung What chemicals are in the white fume you saw in the experiment? Hydrogen chloride (HCl) and ammonia (NH3) What is the major error contributed to percent recovery in this experiment? Spattering of sand, salt or both What attributes to the recovery greater than 100% in this experiment? Sand, salt or both are not dried completely 1 The Iron-copper Molar Ratio-Single Replacement Reaction and Limiting Reagent The quantities of chemical used, copper (II) sulfate pentahydrate and iron metal, are actually in the stoichiometric quantities, and the data sheet of this experiment is not clear, and thus no calculation from this experiment will be asked. What are the color and chemical formula of copper (II) sulfate pentahydrate, respectively? Blue, CuSO4.5H2O What does it mean “limiting reactant or limiting reagent”? The reactant that is used up first or completely during a chemical reaction and thus it limits the amount for product(s) produced. What is the major source of error of this experiment? The replaced Cu metal (molar mass is about 63.55 g/mol) is not washed completely with de-ionized and dried. If any of copper (II) sulfate pentahydrate (molar mass is about 250 g/mol) remains, the error will be huge. Reactions in Aqueous Solutions: Single- and Double-Displacement Reactions: Write its balanced molecular equation and net-ionic equation respectively for zinc metal and hydrochloric acid. Molecular: Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g) Net-Ionic: Zn(s) + 2H+ (aq) Zn2+ (aq) + H2 (g) Write its balanced molecular equation and net-ionic equation respectively for sodium carbonate and hydrochloric acid. Molecular: Na2CO3(aq) + HCl(aq) 2NaCl(aq) + H2O (l) + CO2 (g) Net-Ionic: CO32- (aq) + 2H+ (aq) H2O (l) + CO2 (g) Write its balanced molecular equation and net-ionic equation respectively for calcium chloride and sodium sulfide. Molecular: CaCl2(aq) + Na2S(aq) CaS (s) + 2NaCl (aq) Net-Ionic: Ca2+ (aq) + S2- (aq) CaS (s) Write its balanced molecular equation and net-ionic equation respectively for nickel (II) chloride and silver nitrate. Molecular: NiCl2 (aq) + 2AgNO3 (aq) 2AgCl (s) + Ni(NO3)2 (aq) 2 Net-Ionic: Ag+ (aq) + Cl- (aq) AgCl (s) Write its balanced molecular equation and net-ionic equation respectively for hydrochloric acid and sodium hydroxide. Molecular: HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l) Net-Ionic: H+ (aq) + OH- (aq) H2O (l) Write its balanced molecular equation and net-ionic equation respectively for potassium chloride and sodium nitrate. Molecular: KCl (aq) + NaNO3 (aq) NaCl (aq) + KNO3 (aq) Net-Ionic: There is no net ionic equation. Column Chromatography of Spinach What kinds of pigments are there in spinach? Chlorophyll and beta-carotene are the two main kinds. What does it mean eluent? The eluent is the "carrier" portion of the mobile phase that coming out from the column. It moves the analytes through the chromatograph. In liquid chromatography, the eluent is the liquid solvent; in gas chromatography, it is the carrier gas. Elution is the process of extracting one material from another by washing with a solvent. The eluate, or mobile phase is a combination of the mobile phase "carrier" and the analyte material that emerge from the chromatograph. It specifically includes both the analytes and solutes passing through the column, while the eluent is only the carrier. What does it mean UV-Vis spectrophotometer? This is to ask you write out the whole words of UV-Vis. Ultraviolet-Visible Spectrophotometer or spectrometer Why you can only touch the frosted side of the cuvette or have to wipe the cuvette? 3 The fingerprints may absorb the light and interfere with the results. What does it mean “blank”? A Blank solution is one that does not have any chemical that you are looking for or measuring or detecting. A blank solution is a solution containing little to no analyte of interest, usually used to calibrate instruments such as a colorimeter, UV-Vis spectrometer. A blank solution is the solution prepared accordingly without analyte in there. Molar Mass of a Volatile Liquid: Mass of flask + cap + rubber band 45.6 g Temperature of boiling water 98 oC Barometric pressure 745 mm Hg Mass of flask + rubber band + cap + condensed vapor 45.8 g Mass of condensed liquid __0.2_______________ g Volume of flask 143 mL Molar mass of vapor ______43.42__________ g/mol (Show calculations) PM = dRT ; 1 L= 1000 mL (745/760) x M = (0.2 / 0.143) x 0.082 x (98 +273.15) M = 43.42 Why you need to wipe the aluminum foil inside and outside before you weight it after heating? It may trap water and affects the weighing. 4