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South Pasadena Honors Chemistry Name __________________________________ 4 Salts and Solutions Period ___ Date ___/___/___ Station 1 – ACIDS, BASES, AND NEUTRALS Classify each statement as talking about an [A]cid, [B]ase, or [N]eutral. __B___ feels slippery __N___ CH3OH __A___ tastes sour __A___ H+ donor __B___ KOH __B___ increases [OH-] __A___ turns cabbage juice red __A___ increases [H+] __B___ tastes bitter __A___ H2SO3 __N___ cabbage juice stays purple __B___ NaHCO3 (baking soda) Ammonia, NH3, is a weak base. Cabbage juice would turn _blue_ with NH3. NH3(aq) would be considered a _weak (strong | weak | non) electrolyte. In water, NH3 can be described by the equation: NH3(aq) + H2O(l) NH4+(aq) + OH Indicate one conjugate acid-base pair: _NH3_ and _NH4+__ (or H2O/OH–) NH3 fits the Arrhenius definition of a base because it _increases [OH–]________________. NH3 fits the Bronsted-Lowry definition of a base because it _accepts H+_______________. Draw the solution to the right using + and – for ions and for molecules. Indicate the brightness of the light bulb when testing a solution of NH3(aq). + – South Pasadena Honors Chemistry 4 Salts and Solutions Station 2 – SOLUBILITY RULES Circle the Insoluble Ionic Solids and then list the strong acids and strong bases from memory. MgF2 AgCl CuSO4 Fe(OH)3 NH4Cl CdS PbSO4 CuF2 Na2SO4 NH4OH Sr(NO3)2 BaCO3 PbBr2 CaC2O4 Strong Acids Strong Bases HCl LiOH HBr NaOH HI KOH HNO3 RbOH Hg2I2 CsF Ba(OH)2 Na2CrO4 MgO HC2H3O2 H2SO4 CsOH HClO3 Ca(OH)2 HClO4 Sr(OH)2 HIO4 Ba(OH)2 South Pasadena Honors Chemistry 4 Salts and Solutions Station 3 – SOLUBILITY Is this well-stirred mixture best described as saturated or unsaturated? Justify your answer. Saturated. Undissolved solids (precipitate) indicates there maximum dissolved solutes. Consider a solution of NaCl(aq). Draw four water molecules surrounding each Na+ and Cl ion below. + Na Cl Which of the following solutes dissolve well in the polar solvent, H2O? (check all that apply) soluble ionic solids insoluble ionic solids strong acids strong bases weak acids weak bases nonpolar solutes A test tube has a layer of polar H2O floating on a layer of nonpolar CCl4 (carbon tetrachloride). CH3OH (polar), C6H6 (nonpolar benzene), AgCl, KCl, and I2 (nonpolar) are added to the tube. Which solutes will dissolve in the CCl4 layer? _C6H6_ _I2_ Which solute does not go into either layer? _AgCl___ South Pasadena Honors Chemistry 4 Salts and Solutions Station 4 – SOLUBILITY CURVES The solubility of NH4Cl(s) at 70˚C is _60_g/100 g H2O. How much NH4Cl(s) will dissolve in 40.0 g of H2O? 60 g NH4Cl x = x = 24 g NH4Cl 100 g H2O 40 g H2O If 40.0 grams of H2O, saturated with NH4Cl, is cooled from 70˚C to 50˚C, how many grams of solute should precipitate? __________ 50 g NH4Cl x At 50°C, = x = 20 g NH4Cl 100 g H2O 40 g H2O 24 g – 20 g = 4 g NH4Cl will precipitate 15.0 g NH4Cl dissolved in 40.0 g of H2O at 50˚C would be described as a ______________(unsaturated | saturated | supersaturated) solution. Since 15 g < 20 g, the solution is unsaturated. South Pasadena Honors Chemistry 4 Salts and Solutions Station 5 – pH CALCULATIONS Fill in this chart: [H+] 1.0 × 10-4 M [OH-] 1.0 × 10 pH pOH Acidic/Basic M 4.00 10.00 Acidic 5.0 × 10–12 M 2.0 × 10-3 M 11.30 2.70 Basic 1.0 ×10–5 M 1.0 × 10–9 M 5.0 9.0 Acidic 3.2 × 10–12 M 3.2 × 10–3 M 11.5 2.5 Basic 3.3 × 10-2 M 3.0 × 10–13 M 1.48 12.52 Acidic 1.0 × 10–5 M 1.0 × 10-9 M 5.0 9.0 Acidic 1.6 × 10–2 M 6.3 × 10–13 M 1.8 12.2 Acidic 1.0 × 10–10 M 1.0 × 10–4 M 10.0 4.0 Basic –10 South Pasadena Honors Chemistry 4 Salts and Solutions Station 6 – MOLARITY CALCULATIONS A 2.00 mole sample of NaOH is dissolved in enough water to make 500. mL of solution. What is the concentration of the solution? n = 2.00 mol V = 0.500 L M=? n 2.00 mol M= = = 4.00 M V 0.500 L 60.0 grams of NaOH (MM = 40.00 g·mol-1) is dissolved in enough water to make 0.750 L of solution. What is the concentration of the solution? 1 mol n = 60 g V = 0.750 L M=? = 1.5 mol 40.00 g n 1.5 mol M= = = 2.0 M V 0.750 L A 250. mL sample of a 0.125 M solution of NaOH contains ________ grams of NaOH. n=? V = 0.250 L M = 0.125 M n = M × V = (0.125 M)(0.250 L) = 0.0313 mol 40.00 g 0.0313 mol = 1.25 g 1 mol South Pasadena Honors Chemistry 4 Salts and Solutions Station 7 – MORE MOLARITY PROBLEMS Rank these three solutions from most dilute to most concentrated: __X___ = __Y___ < __Z___ X: 10. g solute in a 300. mL solution X and Y have the same concentration! Y: 20. g solute in a 600. mL solution Z: 20. g solute in a 300. mL solution You need to prepare 2.00 L of 3.00 M HCl. What volume of stock (12.1 M HCl) do you need? Mc = 12.0 M Vc = ? Md = 3.00 M Vd = 2.00 L McVc = MdVd MdVd (3.00 M)(2.00 L) Vc = = = 0.500 L Mc (12.0 M) Consider a 0.200 M solution of aluminum sulfate, Al2(SO4)3. [Al3+] = __0.400 M______ [SO42] = _0.600 M________ South Pasadena Honors Chemistry 4 Salts and Solutions Station 8 – WEAK ACID EQUILIBRIA HF is a weak acid. Finish the dissociation equation for HF. HF(aq) F– + H+ (I shouldn’t have included the H2O --Groves) The Ka for HF is 7.0 x 10-4. Write the equilibrium expression for HF. [H+][F–] Ka = [HF] Use the ICE Box below to calculate the H+ concentration in a 1.0 M solution of HF. HF H+ + F– Initial 1.0 0 0 Change –x +x +x Equilibrium 1.0 – x x x + – 2 [H ][F ] (x)(x) x Ka = = = = 7.0 × 10–4 x = [H+] = 0.026 M [HF] (1.0 – x) 1.0 What is the % dissociation of a 1.0 M HF solution? 0.026 % dissociation = ×100% = 2.6% 1.0 South Pasadena Honors Chemistry 4 Salts and Solutions Station 9 – LOOSE ENDS Solids dissolve best in __hot______ (hot | cool) water. Gases dissolve best in __cool_______ (hot | cool) water. Gases dissolve best when the gas pressure above the solvent is __high_____ (high | low). O2(g) would dissolve in water best: (A) 20C and 2 atm pressure (B) 50˚C and 5 atm pressure (C) 20˚C and 5 atm pressure (D) 50˚C and 2 atm pressure Rate these weak acids from weakest to strongest. HNO2 Ka = 4.0 × 10−4 HC2H3O2 Ka = 1.8 × 10−5 HOCl Ka = 3.5 × 10−8 HCN Ka = 6.2 × 10−10 HCN < HOCl < HC2H3O2 < HNO2