Solubility Unit PDF

Solubility unit Dissolving ionic solids Ionic compounds arrange themselves to increase attractive forces between ions and to decrease repulsive forces between ions. This arrangement is known as a crystal structure (lattice). *Polar solvent molecules will surround each ion *When ions are separate...

Solubility unit Dissolving ionic solids Ionic compounds arrange themselves to increase attractive forces between ions and to decrease repulsive forces between ions. This arrangement is known as a crystal structure (lattice). *Polar solvent molecules will surround each ion *When ions are separated it is called dissociation *When solute molecules are surrounded by solvent molecules it is called solvation *If the solvent is water, it is called hydration Dissolving covalent solids > covalent molecules are held together by weak intermolecular forces >during solvation each molecule is surrounded by solvent molecules Writing dissolving equations > solvents dont show up in the equation >ionic solids separate into ions (ex NH4NO3------->NH4(aq) + NO3) >covalent solids just separate between molecules (ex. C6H12O6(S)-----> C6H12O6(aq)) Definitions Undersaturated: solution contains less than the max amount of solute that can be dissolved (dissolving>crystalizing). Saturated solution: contains the max amount of solute that can be dissolved (dissolving = crystallization). Super-saturated: under special conditions, solution contains more than the max amount of solute, but crystallization does not occur. Dissolving and crystallization occur at the same rate in a saturated solution, this is called equilibrium. The max amount of dissolving that can occur is known as the solubility of a solute. Solute = grams of a solute that can dissolve in 100ml H2O at a given temperature The solubility of solids in liquids tends to increase with temperature The solubility of gasses in liquid tends to decrease with temperature 3 factors affecting solubility 1. Nature of solute and solvent “like solves like” >particles must attract each other for dissolving to occur *Greater attraction=greater solubility >different substances will have different solubilies in a given solution >polar dissolves polar, non-polar dissolves non-polar. 2. Temperature >the solubility of a solid or liquid solute will usually increase with temperature *Increase temp=increase solubility, ex. Sugar in hot tea VS sugar in cold tea. Exception: the solubility of ALL GASSES decreases with an increase in temperature. *Gases escape more quickly *Particles have greater kinetic energy and can escape the solution more quickly, ex. Cold pop VS warm pop. 3. Pressure >only applies to solutions of gasses in liquids > henrys law: the solubility of gasses in liquids is directly proportional to the pressure of the gas above the liquid 4 factors affecting the rate of dissolving (find other 2????) 1. Surface area >when a solute dissolves, the action takes place only around the surface of each particle. >increase in surface area = increase in solute-solvent collisions, ex. Dissolving a cube of sugar VS a tbsp. 2. Amount of solute already dissolved >as the solution approaches the point where no more solute can be dissolved, dissolving takes place slower than if it were being dissolved in pure solvent. Solubility notes >the solubility of t=a solution is determined by the mass of a solution >undersaturated is any point below the solubility curve > any point above is supersaturated >the line tells you the maximum amount to be saturated. Colligative properties A colligative property is a property of a solution that depends on the concetration of a solute (the number of solute particles dissolved) but NOT the type of solute. 3 colligative properties *Vapor pressure reduction *Boiling point elevation *Freezing point depression Vapor pressure >the pressure directly above the surface of a liquid, exerted by the molecules that have evaporates >low vapor pressure = not much evaporation >high vapor pressure = lots of evaporations Vapor pressure reduction >solute interferes with vaporization (blocking the exit for water molecules) therefore, lowers the vapor pressure of a solution Boiling point elevation >boiling point is closely tied to vapor pressure; therefore, the water needs more heat to boil since the vapor pressure is lower. >since vapor pressure is lowered, boiling point is elevated. Freezing point depression > the presence of a solute in water disrupts the formation of the ordinary pattern of ice. Therefore, more kinetic energy must be withdrawn to form a solution than from pure solvent to cause the solution to solidify because the particles need to get closer together. Difference between mixtures and solutions >solutions are homogenous mixtures that are uniform is composition with a single phase >mixtures can be heterogenous where the substances that make them up remain distinct Suspension and colloids >A suspension is a heterogeneous mixture that settles out if left undisturbed. > the particles in a colloid are much smaller than those in a suspension and do not settle out  Dissociation equations A dissociation equation is the equation used to show a chemical has dissolved It usually looks something like AB ------> A+ + B-. Just breaking down a compound into simple ions. If a question asks if a chemical is an electrolyte or not it is asking is the chemical can be dissolved in water and produce ions that allow the solution to conduct electricity Bringing back mole calculations Molarity (M) (concentration) expresses solutions concertation M= moles of solute ÷ liters of solution Molarity, molar, M, Mol/liter and concentration all mean the same thing. 1.3M = one point three molar How to solve how many moles of ____ are in how many liters of solute questions How many grams of solute are in 2.5L 0.3M cacl Step one setup the question 0.3= mol/2.5L Then multiple by 2.5 on each side to cancel out liters (2.5)0.3=mol/2.5 (2.5) =.75=.75mol cacl Step two: convert to grams.75gCaCl x 111.1g CaCl= 83g CaCl 1mol What is the concentration of s solution that contains 30g of potassium chloride in 1.8L of water Step one: find moles of potassium chloride 30g x 1 mol = 0.402m KCl 74.55 Step two: plug it into the formula M= 0.402mol KCl = 0.2M 1.8L water How to do mixing and dilution problems What volume of concentrated H2SO4 (18M) is needed to make 1.5L of a 2M H2SO4 solution? Step one: identify what values go where M1= 18M (because it is the initial Molarity) V1=? (because that is the volume needed to make the solution) M2=2M (because it is the final molarity of the diluted solution) V2=1.5L (because it is the final volume of the diluted solution So (18M) (?L) =(2M) (1.5L) Step two: solve for V1 by getting the variable alone V1= (2M)(1.5L) 18M V1= 0.167 L Step three (optional): convert into ML 0.167 x 1000 = 167ML Your final answer in that 167 ML is needed to make 1.5L of a 2M solution To 180 ML of a 1.5 M NaCl solution 10g of NaCl is added. Find the molarity of the new solution. Step one: find the mol of NaCl in the original solution Using the M=mol/L we can find the amount of NaCl in the original solution 1.5M= ?/.18L Now multiply by.18 on each side 1.5M x.18 =.27 The mol of NaCl in the original solution is.27mol Step two: calculate the added NaCl into mols Na= 22.989 Cl= 35.457 NaCl = 58.441 10g ÷ 58.441g = 0.17mol added Step three: add to the amount of mols in the original solution 0.27+0.17= 0.44mol Step four: use molarity formula ?=.44mol/.18L = 2.44M So, the molarity of the new solution is 2.44M If 150 Ml of 2M solution is mixed with 550ml of a 3.5 M solution, whats is the volume and the molarity of the resulting solution? Step one: find the mol of chemical in each solution Solution one: 2M= ?/.15 = 2M=.3mol/.15 Solution two: 3.5=?/.550 = 3.5=1.925mol/.550 Step two: add the mols and liters.3+1.925= 2.225mol.15+.550= 0.700L Step three: plug it into the formula M=2.225/0.7 3.17=2.225/0.7 Harder stuff What mass of Mg will react with 1.5L of 3.5M solution of HCl by the following reaction: Mg + 2HCl ---------> MgCl2 + H2 Step one: determin the moles of HCl 3.5 = ? 1.5 3.5 x 1.5 = 5.25 mol of HCl Step two: use reaction stoichiometry Looking at the balanced equation you see that 2 moles of HCl react with 1 mole of mg Mg + 2HCl ---------> MgCl2 + H2 So to find the moles of Mg you need to divide the mols of HCl by 2 to cacel it out 5.25 x 1mol Mg = 2.625mol Mg 2mol HCl Step three: convert into grams 2.625 x 24.31 = 63.85 So the final answer is 63.85g of Mg (ok that honestly wasn't that bad)x When H2SO4 is mixed with NaOH, water and Na2SO4 are formed. What mass of NaSO4 is formed when 500ml of a 4.5M solution of H2SO4 is mixed with an excess of NaOH? Step one: write a balanced chemical equation H2SO4 + 2NaOH -------> Na2SO4 +2H2O We can see from the balanced equation that 1 mole of H2SO4 reacts with 2 moles of NaOH to produce 1 mole of Na2SO4 Step two: calculate the moles of H2SO4 4.5 = ? 4.5x.5 = 2.25 mol H2SO 4.5L Step three: use reaction stoichiometry to find the moles of Na2SO4 We can see that there is no coefficient in front of Na2SO4 or H2SO4 which means 1 mole of H2SO4 produces 1 mole of Na2SO4. So, 2.25 x 1mol Na2SO4 = 2.25mol Na2SO4 1mol H2SO4 Step four: convert to grams Na2 = 45 S= 32.07 O4= 63.96 140.96 x 2.25mol= 317g Na2SO4 The mass of Na2SO4 formed is 317.1 grams.