Preparation for General Chemistry Skills Class Worksheet 4

Choose the aqueous solution that has the lowest freezing point. These are all solutions of nonvolatile solutes and you should assume ideal van't Hoff factors where applicable. a. 0.100 m NaNO3; i=2: -2(0.100)k_f = -0.200k_f b. 0.100 m Li2SO4; i=3: -3(0.100)k_f = -0.300k_f c. 0.200 m C6H12O6; i=1: -1(0.200)k_f = -0.200k_f d. 0.100 m Na3PO4; i=4: -4(0.100)k_f = -0.400k_f e. They all have the same freezing point. Glycerol (C3H8O3) is a nonvolatile nonelectrolyte with a density of 1.26 g/mL at 25 degrees C. Calculate the vapor pressure of a solution made by adding 50.0 mL of glycerin to 500.0 mL of water. The vapor pressure of pure water at 25 degrees C is 23.8 torr. The molar mass for C3H8O3 is 92.1 g/mol? Vapor pressure of the solution Use Raoult's Law P1 = X1 * P1 degrees Need to find X of water because glycerin has no VP. X_H2O = moles H2O / (moles H2O + moles glycerin) To find moles H2O: n_H2O = 500.0 mL H2O * (1.00 g / 1 mL) * (1 mol / 18.02 g) = 27.747 mol H2O To find moles glycerin: n_C3H8O3 = 50.0 mL * (1.26 g / 1 mL) * (1 mol / 92.1 g) = 0.684 mol X_H2O = 27.747 mol H2O / (27.747 mol H2O + 0.684 mol C3H8O3) = 0.97594 P1 = (0.97594) * (23.8 torr) = 23.222 torr Section 3 : Chemical Quantities and Stoichiometry 3-1 -> area of study devoted to the quantities of materials consumed and produced in a reaction. @ Atomic Masses -> in 1961 a system was devised to assign atomic masses to each element -> to do this, a "standard" was needed. -> an isotope of carbon, carbon-12 (C-12), was used as the standard and was assigned a value of exactly 12 amu -> amu = atomic mass units So, why is carbon's atomic mass 12.01 amu on the Periodic Table? -> Answer: most elements occur as a mixture of isotopes and natural carbon is found as 98.89% C-12 and 1.11% C-13 atoms -> So, (.9889)(12 amu) + (.0111)(13 amu) = 12.01 amu -> atomic mass is a "weighted avg." of isotopes this is why atomic masses of elements are expressed as decimals on the Periodic Table -> note that not a single carbon atom weighs 12.01 amu!! This is an average weight. Ex: lithium (Li) <-> 6.941 amu The vapor pressure of dichloromethane was measured as a function of temperature, and the following results were obtained. Relationship between V.P. & Temp is expressed in Clausius-Clapeyron. 2 forms: ln P = -Delta H_vap / R (1/T) + B Temperature (K) Vapor Pressure (mm Hg) 200. 0.800 220. 4.30 240. 21.0 260. 71.0 280. 217 300. 501 Експортувати в Таблиці a.) Use graphical method to determine the heat of vaporization of dichloromethane. From the graph, obtain slope m = -Delta H_vap / R b.) What is the normal boiling point for dichloromethane? Ethylene glycol, C2H4(OH)2, is a colorless liquid used as automobile antifreeze. If the density at 20 degrees C of a 1.028 m solution of ethylene glycol in water is 1.0241 g/mL, what is the molarity of the solution? The molar mass of ethylene glycol is 62.07 g/mol. Problem: Convert m to M moles C2H4(OH)2 / kg H2O -> moles C2H4(OH)2 / L SOLUTION solute + solvent moles C2H4(OH)2 / kg H2O + g C2H4(OH)2 moles C2H4(OH)2 / 1 x 10^3 g H2O + g C2H4(OH)2 Important Numbers One Electron Charge e = 1.602 x 10^-19 C Electrostatic Constant k = 8.99 x 10^9 Nm^2/C^2 Avogadro # 1 mole = 6.02 x 10^23 atoms Gravitational Constant G = 6.67430 x 10^-11 Conversion atm <-> C 1 atm = 1.013 x 10^5 Pa 1C = 10^-6 uC = 10^-9 nC Important Equations Coulombs Law Fe = k q1q2 / r^2(12) For Two Point Charges: Fe = Electric Force k = Coulomb's Constant q1, q2 = charge on objects r = distance between objects Electric Force due to an electric field F = QE F = electric force Q = (Test Charge) E = Electric Field E = F/Q Electric Field at Point P E(p) = Sum (kQ / R^2) R-hat R = distance from P to charge Q Q = Charge creating field R-hat = Unit vector from P to Q Superposition of electric charges F = kQ Sum (qi / ri^2) (ri-hat) Sum is over individual point charges For Continuous Charge lambda = Q/L sigma = Q/A X/Y sqrt(3) sqrt(3) (units in equation) 2m 60 degrees Chapter 2 Stuff F = k q1 q2 / r^2 E1 = 3.854 x 10^-22 E = k Q/R^2 E = F/Q E = lambda / (2 pi epsilon_0 R) (Line) Area of sphere = 4 pi R^2 Area of cylinder = 2 pi r L epsilon_0 = 8.85 x 10^-12 Integral E.dA = Q_enc / epsilon_0 (Gauss' Law) Flux = EA Cos theta Work = FD Work = 1/2 mv^2 Potential Difference V = U/q U = PE V = Integral E . ds Exponent Rules Product: a^x a^y a^z = a^(x+y+z) Quotient: a^x / a^y = a^(x-y) Power: (a^x)^y = a^(xy) Power of Product: (ab)^x = a^x b^x Power of a Fraction Rule: (a/b)^x = a^x / b^x Zero Exponent: a^0 = 1 Negative Exponent: a^-x = 1/a^x Fractional Exponent: a^(x/y) = y-th_root(a^x)