Version 001 Calculating Concentrations WKST vanden bout (51165) 1

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1 Version 001 Calculating Concentrations WKST vanden bout ( This print-out should have 22 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. ChemPrin3e G (part 1 of points Determine the mass of anhydrous copper(ii sulfate that must be used to prepare 250 ml of 1.9 M CuSO 4 (aq. Correct answer: g. V 250 ml 0.25 L FW CuSO g/mol g/mol + 4( g/mol g/mol M 1.9 M m CuSO4 (1.9 M(0.25 L( g/mol g 002 (part 2 of points Determine the mass of CuSO 4 5H 2 O that must be used to prepare 250 ml of 1.9 M CuSO 4 (aq. Correct answer: g. FW CuSO4 5H 2O FW CuSO4 +5(FW H2O g/mol + 10( g/mol + 5( g/mol g/mol m CuSO4 5H 2O (1.9 M(0.25 L( g/mol g points A chemist studying the properties of photographic emulsions needed to prepare 500 ml of M AgNO 3 (aq. What mass of silver nitratemustbeplacedintoa500mlvolumetric flask, dissolved, and diluted to the mark with water? Correct answer: g. v 500 ml 0.5 L M M FW AgNO g/mol g/mol + 3( g/mol g/mol m AgNO3 (0.178 M(0.5 L ( g/mol g Brodbelt points How much NaNO 3 is needed to prepare 225 ml of a 1.55 M solution of NaNO 3? g g correct g g g V 225 ml M 1.55 M? g NaNO ml 1 L soln 1000 ml 1.55 mol NaNO 3 1 L soln 85 g NaNO 3 1 mol NaNO g NaNO 3 ChemPrin3e G 05 Brodbelt 03 13

2 Version 001 Calculating Concentrations WKST vanden bout ( points How many moles of HCl are present in 40.0 ml of a M solution? mol mol mol mol mol correct V 40.0 ml M M?molHCl 40.0mLsoln 1 L mol HCl 1000 ml 1 L soln mol HCl Brodbelt points What is the final concentration of Ca(OH 2 when 255 ml of M Ca(OH 2 is mixed with 55.0 ml of 0.65 M Ca(OH 2? M M M M M M correct V 1 Ca(OH2 255 ml [Ca(OH 2 ] M V 2 Ca(OH2 55 ml [Ca(OH 2 ] M The total moles of Ca(OH 2 in the final solution will be the sum of the moles present in the two individual solutions:? mol Ca(OH 2 (soln L soln mol Ca(OH 2 1 L soln molca(oh 2? mol Ca(OH 2 (soln L soln 0.65 mol Ca(OH 2 1 L soln molca(oh 2 Total mol Ca(OH mol mol molca(oh 2 The total volume of the final solution is the sum of the volumes of the individual solutions. Total L L L 0.31 L soln Molarity is moles solute per L of solution.? M Ca(OH mol Ca(OH L soln M Ca(OH 2 Msci points What is the effective molality of a solution containing 12.0 g of KI in 550 g water? Assume 100 percent ionic dissociation molal molal correct molal molal molal molal m KI 12.0 g m H2O 550 g Because KI is a 1:1 salt, you get one cation and one anion for every single formula unit

3 Version 001 Calculating Concentrations WKST vanden bout ( that dissolves. Therefore, you ll get a DOU- BLING of the stated molality for the effective molality. The formula weight of KI is 166 g/mol, so the number of moles of KI is ( 1 mol KI 12.0 g KI mol KI, 166 g KI and the (stated molality of the solution would then be mol KI m kg H 2 O But recall that the effective molality would be twice the stated molality here, so the effective molality is m. Nlib points If you mix 3 moles of ethylene glycol (antifreeze in 4165 grams of water, what is the molality of the solution? Correct answer: m. n ethylene glycol 3 mol m water 4165 g Molality (m is moles solute per kilogram of solvent. The solute is ethylene glycol. The solvent is water and 4165 g kg.? m 3 mol ethylene glycol kg H 2 O m Nsci points 1.9 g of NaCl and 6.1 g of KBr were dissolved in48gofwater. What isthemolalityofnacl in the solution? Holt da 13 1 sample points What is the molarity of a L solution that is made from g of NaCl? Correct answer: M. V solution L M? m NaCl g M L soln? mol NaCl g NaCl ( 1 mol NaCl g NaCl mol NaCl mol NaCl? M L soln M mol L Molality 08 44a points Calculate the molality of sucrose in a solution composed of g of sucrose (C 12 H 22 O 11 dissolved in 606 ml of water. Correct answer: m. m C12H 22O g V H2O 606 ml L MW C12H 22O g/mol Correct answer: m. m NaCl 1.9 g m water 48 g m KBr 6.1 g ( 1 kg m H2O (0.606 L kg 1 L Thus the molality is mol NaCl m NaCl kg water 1.9 g 58.4 g mol 1 NaCl kg water m moles solute m C12H 22O 11 ( g sucrose g/mol sucrose kg H 2 O m

4 Version 001 Calculating Concentrations WKST vanden bout ( Msci points What additional information, if any, would enable you to calculate the molality of a 7.35 molar solution of a nonelectrolyte solid dissolved in water? 1. Both the density of the solution and the molecular weight of the solute would be needed. correct 2. Only the density of the solution would be needed. 3. Only the molecular weight of the solute would be needed. 4. Only the density of water would be needed. 5. None is needed. molarity molality L solution The density of the solution can be used to convert volume (1 L of solution into mass of solution. Then the molecular weight of the solute (given or calculated from the formula can be used to convert the number of moles solute in 1 L solution into mass of solute in grams. The mass of the solvent is the difference between the mass of the solution and the mass of the solute (both of which have been calculated. Substitute the values into the molality formula and calculate. Molality 08 46c points Calculate the molality of 10.5 M NH 3 (aq with a density of g/cm 3. d g/cm 3 Assume 1 L of 10.5 M NH 3 (aq; it will contain 10.5 mol NH 3 with a mass of (10.5 mol( g/mol g. The density of the 1 L of solution is g/cm cm3 1 L g/l, so the total mass of the solution is g, which leaves g g g of water. Therefore, the molality is m 10.5 mol NH m. Nsci points Formalin is a solution of 40.0% formaldehyde (H 2 CO,10.0%methylalcohol(CH 3 OH,and 50.0% water by mass. Calculate the mole fraction of methyl alcohol in formalin. Correct answer: In a 100 g formalin, solution the masses are formaldehyde 40.0 g, methyl alcohol 10.0 g, and water 50.0 g. n CH3OH +n H2CO +n water 10 g 32 g/mol + 40 g 30 g/mol + 50 g 18 g/mol mol The mole fraction of methyl alcohol is X n CH 3OH 10.0 g 32.0 g/mol mol Correct answer: m. MW g/mol M 10.5 M Nsci points Toluene (C 6 H 5 CH 3 is a liquid compound

5 Version 001 Calculating Concentrations WKST vanden bout ( similar to benzene (C 6 H 6. Calculate the mole fraction of toluene in the solution that contains 112 g toluene and 72.0 g benzene. Correct answer: m toluene 112 g m benzene 72.0 g ( 1 mol n toulene (112 g toluene g 1.21 mol ( 1 mol n benzene (72.0 g benzene g mol The total number of moles of all species present is 1.21 mol mol 2.13 mol The mole fraction of toluene is then X toluene n toluene 1.21 mol 2.13 mol Msci points The mole fraction of a certain nonelectrolyte compound in a solution containing only that substance and water is The molecular weight of water is 18.0 g/mol. What additional information is needed to determine the molality of the solution? 1. The density of the solute. 2. The density of the solution. 3. The molecular weight of the compound. 4. The mole fraction of water in the solution. 5. No additional information; the molality can be calculated from the information given. correct Here we can assume that we have 1 mol total. (In fact, we can choose any number of moles, but the math is easier if you choose 1 mol. If the mole fraction of the substance is 0.100, you can then assume that you have mol of the substance, and the remaining mol is H 2 O. The molality of a solution is determined by the following formula: m We ve already assumed that we have mol of solute, and we can determine the kg of H 2 O in the usual way: ( 18.0 g 1 mol ( 1 kg mol H 2 O 1000 g kg, and we can calculatethe molalityof thissolution: m mol kg H 2 O 6.17 m So, it is possible to determine the molality of this solution without any additional information. Msci points The molecular weight ofsugar is342 and that of water is What is the mole fraction of sugar in a 2.00 molal solution of sugar dissolved in water? 1. mole fraction correct 2. mole fraction mole fraction mole fraction mole fraction MW sugar 342 MW water m sugar 2.00 m Molality Molality of sugar 2.00 mol sugar 1 kg water Mol water in 1 kg water ( 1 mol water (1000 g water g water 55.5 mol H 2 O

6 Version 001 Calculating Concentrations WKST vanden bout ( The mole fraction of sugar is mol sugar X sugar mol sugar+mol water 2.00 mol 2.00 mol+55.5 mol Nsci exam points 11.6g ofnacl(58.4g/moland 16.9gofKBr (119.8 g/mol were dissolved in 49 g of water (18.0 g/mol. What is the mole fraction of KBr in the solution? Correct answer: m NaCl 11.6 g m KBr 16.9 g m water 49 g FW NaCl 58.4 g/mol FW KBr g/mol FW water 18.0 g/mol 11.6 g n KBr mol g/mol n NaCl 16.9 g mol 58.4 g/mol 49 g n H2O mol 18.0 g/mol Since n KBr +n NaCl +n H2O, mol mol mol mol, the mole fraction is n KBr mol X KBr mol mol Correct answer: g. m water 100 g X sucrose 0.3 n water X sucrose n 100 g 18.0 g/mol mol n 0.3 n+n water n 0.3(n+n water 0.7n 0.3n water n 0.3n water m g/mol, so (342 g/mol(0.3( mol m g Nsci points A solution is made from 596 ml methanol (CH 3 OH of density g/ml and 82 ml of water (H 2 O of density g/ml. Assume that the solution behaves ideally and the volumes are additive. Calculate the mole fraction of methanol in this solution. Correct answer: V methanol 596 ml V water 82 ml density methanol g/ml density water 1.00 g/ml mole fraction CH 3 OH n CH 3OH Nsci points How many grams of sucrose (C 12 H 22 O 11 must be dissolved in 100 g water to make a solution in which the mole fraction of sucrose is 0.3? n CH3OH 82 ml CH 3 OH g CH 3OH 1.0 ml CH 3 OH 1.0 ml CH 3OH 32.0 g CH 3 OH 14.9 mol CH 3 OH

7 Version 001 Calculating Concentrations WKST vanden bout ( ( 1.0 ml H2 O n n H2O 82 ml H 2 O total 0.14 mol P total 700 torr 18.0 g H 2 O n H mol mol H 2 O The mole fraction is 14.9 mol X CH3OH 14.9 mol mol Holt da 10 rev points Three of the primary components of air are carbon dioxide, nitrogen, and oxygen. In a sample containing a mixture of only these gases at exactly one atmosphere pressure, the partial pressures of carbon dioxide and nitrogen are given as P CO torr and P N torr. What is the partial pressure of oxygen? Correct answer: torr. P CO torr P T 1atm 760torr P N torr P O2? X H2 n H mol 0.14 mol P H2 X H2 P total ( (700 torr 100 torr P T P CO2 +P N2 +P O2 P O2 P T (P CO2 +P N2 P O2 760 torr (0.285 torr torr P O torr Mlib points A 22.4 L vessel contains 0.02 mol H 2 gas, 0.02 mol N gas, and 0.1 mol NH 3 gas. The total pressure is 700 torr. What is the partial pressure of the H 2 gas? torr correct 2. 7 torr 3. None of these torr torr