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# Biotech math problems_part1_answers (1)

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### Biotech math problems_part1_answers (1)

1. 1. Practice Problems, Part 1: Molarity, molality, NormalitySolve each problem on your own paper. Be sure to show: • Information the problem gives you- numbers and its description • Set up of the math • Doing the math; use dimensional analysis whenever possible • Answer before rounding • Answer after rounding • No naked numbers- put units on all numbers1. Calculate the Molarity of a solution that has 2.3 moles dissolved in 4.6liters total.2.3 moles4.6 liters of solutionNeed to solve for MolarityMoles =?Liters2.3 moles = 0.50 moles/L = 0.50M4.6 liters2. Calculate the molality of a solution that has 1.5 moles added to 675 mL ofsolvent.1.5 moles675 mL of solventNeed to convert mL to LNeed to solve moles/L675 mL x 1L = 0.675 L 1000mL1.5 moles = 2.2222 moles =2.2 moles/liter = 2.2 m0.675 L 1 L of solvent3. Calculate the Molarity of 23.5 grams of silver nitrate, AgNO 3, that isdissolved in water for a final volume of 750 mL.23.5 g AgNO3750 mL final volumeNeed to convert g to molesNeed to convert 750 mL to L Getz 2007
2. 2. Need to use equation moles/literAg = 107.9 g/molN = 14.0 g/mol3 oxygens = 3 (16.0) = 48.0 g/mol107.9 + 14.0 + 48.0 = 169.9 g/mol23.5 grams x 1 mol = 0.1383 mol = 0.138 mol 169.9 g750 mL x 1L = 0.75 L 1000 mL0.138 mol = 0.1844 mol/L = 0.18 mol/L = 0.18 M0.75 L4. How many grams of CuSO4 ⋅ 5H2O do you need to make 800. mL of a 0.6 Msolution? Remember to calculate the molar mass of this chemical you figureout the mass of Cu, S, four oxygens, and five waters. You treat the ⋅ as a +not as an x.800. mL0.6 MNeed grams of CuSO4 ⋅ 5H2ONeed to figure out mol of CuSO4 ⋅ 5H2O then how many grams it is.Convert 800. mL to L800.mL x 1L = 0.8 L 1000mL0.8 L x 0.6 mol = 0.48 mol 1LCu = 63.5 g/molS = 32.0 g/molO = 16.0 g/mol so 4- O = 64.0 g/molH2O = 18.0 g/mol so 5 H2O = 90.0 g/molMolecular weight of copper (II) sulfate =0.48 mol x 249.5 g = 119.76 g 1 mol Getz 2007
3. 3. 5. You have 20.0 grams of Pb(NO3)2. You put it in water and bring the finalvolume to 50.0 mL. What is the Molarity?20.0 grams50.0 mLNeed to convert g to molNeed to convert 50.0 mLNeed to use equation moles/literPb = 207.1 g/mol2 N = 2(14) = 28.0 g/mol6- O = 6(16)= 96.0 g/mol207. 1 + 28.0 + 96.0 = 331.1 g/mol20.0 g x 1 mol = 0.0604 mol 331.1 g50.0 mL x 1L = 0.050 L 1000mL0.0604 mol = 1.208 mol/L = 1.2 mol/L = 1.2 M0.050 L6. What is the normality of a 2 M solution of H3PO4?2 moles of H3PO4 x 3 moles H+ = 6 moles H+ so 6N1 liter 1 mole of H3PO4 1 liter7. How many grams of NaOH are in 400.0 mL of a 0.5 M solution of NaOH?400.0 mL0.5 MNeed to convert 400.0 mL to LNeed to figure out molecular weight of NaOH400.0 mL x 1L = 0.4000 L 1000mL0.4000 L x 0.5 mol = 0.2 mol 1L Getz 2007
4. 4. Na = 23.0 g/molO= 16.0 g/molH = 1.0 g/molNaOH = 40.0 g/mol0.2 mol x 40.0 g = 8.0 g 1 mol8. We need 850.0 mL of a 0.45 M solution of NaHCO 3. How much NaHCO3 dowe weigh?850.0 mL0.45 MConvert 850.0 mL to LNeed to figure out molNeed to figure out molecular weight of NaHCO3 to get to g of NaHCO3850.0 mL x 1L = 0.8500L 1000mL0.8500 L x 0.45 moles = 0.3825moles 1LNa= 23.0 g/molH= 1.0 g/molC = 12.0 g/mol3- O = 48.0 g/molNaHCO3= 84.0 g/mol0.3825 moles x 84.0 g = 32.13 g = 32.1 g or 32 g 1 mol9. Which solution will have a greater volume?a. 58.5 g of NaCl in water to make 1000 mL of solutionb. 58.5 g of NaCl added to 1000 mL of waterb will have a greater volume, even though it will not be that much greater Getz 2007
5. 5. 10. Identify the descriptions in problem 9a and 9b as being either Molarityor molality.a. Molarityb. molality11. Calculate the Molarity or the molality for the descriptions in 9a and 9b.You need to do question 10 first; figure out which one is a description ofMolarity and which is molality first. Make sure you use the proper units.NaCl = 58.5 g/molSo for 9a it would be 1 M and for 9b it would be 1 m58.5 g x 1 mol = 1 mol 58.5 g Getz 2007