Chapter 4 Solutions and Solution Stoichiometry
Solutions Homogeneous mixtures are called solutions. The component of the solution that changes state is called the solute. The component that keeps its state is called the solvent. If both components start in the same state, the major component is the solvent.
Kinds of Solutions Gas in gas Air (O Gas in liquid Gas in solid Liquid in liquid Liquid in solid Solid in liquid Solid in solid Carbonated water (CO H Gasoline, tequila Dental amalgam (Hg in Ag) Salt water (NaCl in H Sterling silver (Cu in Ag)
Solvent and Solute in an Aqueous Solution
Solvent and Solute in an Aqueous Solution
The Solution Process
What Happens When a Solute Dissolves? There are attractive forces between the solute particles holding them together. There are also attractive forces between the solvent molecules. When we mix the solute with the solvent, there are attractive forces between the solute particles and the solvent molecules. If the attractions between solute and solvent are strong enough, the solute will dissolve.
Table Salt Dissolving in Water In the case of an ionic compound each ion is attracted to the surrounding water molecules and pulled off and away from the crystal.
Sugar Dissolving in Water In the case of a molecular compound, each molecule is surrounded by water molecules and pulled off and away from the crystal.
Electrolytes and Nonelectrolytes
Salt vs. Sugar Dissolved in Water Ionic compounds dissociate into ions when they dissolve. Molecular compounds do not dissociate into ions when they dissolve.
Electrolytes and Nonelectrolytes Materials that dissolve in water to form a solution that will conduct electricity are called electrolytes. Materials that dissolve in water to form a solution that will not conduct electricity are called nonelectrolytes.
Acids Acids are molecular compounds that ionize when they dissolve in water. The molecules are pulled apart by water. The percentage of molecules that ionize varies. Acids that ionize virtually 100% are called strong acids. HCl(aq) H + (aq) + Cl (aq) Acids that only ionize a small percentage are called weak acids. HF(aq) H + (aq) + F (aq)
Strong and Weak Electrolytes Strong electrolytes are materials that dissolve completely as ions. 1) ionic compounds and strong acids 2) The solutions conduct electricity well. Weak electrolytes are materials that dissolve mostly as molecules, but partially as ions. 1) weak acids 2) The solutions conduct electricity, but not well.
Dissociation vs Ionization When ionic compounds dissolve in water, the anions and cations are separated from each other. This is called dissociation. Na 2 S(aq) 2 Na + (aq) + S 2- (aq) ompounds containing polyatomi When compounds containing polyatomic ions dissociate, the polyatomic group stays together as one ion. Na 2 SO 4 (aq) 2 Na + (aq) + SO 4 2 (aq) en in water, the When strong acids dissolve in water, the molecule ionizes into H+ and anions. H 2 SO 4 (aq) 2 H + (aq) + SO 4 2 (aq)
Write the equation for the process that occurs when the following strong electrolytes dissolve in water CaCl2 HNO3 (NH4)2CO3 CaCl2(aq) Ca 2+ (aq) + 2 Cl (aq) HNO3(aq) H + (aq) + NO3 (aq) (NH4)2CO3(aq) 2 NH4 + (aq) + CO3 2 (aq)
The Real Picture of Acid Ionization HCl H + + Cl H Cl H H [ ] + O H O + H H + - Cl strong acid water HCl + H2O H3O + + Cl hydronium ion chloride ion
Solubility
Solubility of Ionic Compounds Some ionic compounds, such as NaCl, dissolve very well in water at room temperature. Other ionic compounds, such as AgCl, dissolve hardly at all in water at room temperature. Compounds that dissolve in a solvent are said to be soluble, where as those that do not are said to be insoluble.
Solubility Rules Compounds that Are Generally Soluble in Water Compounds Containing the Following Ions are Generally Soluble Li NO Cl Ag Exceptions Insoluble none none SO Ag
Solubility Rules Compounds that Are Generally Insoluble in Water Compounds Containing the Following Ions are Generally Insoluble CO OH- S Exceptions Soluble or Slightly Soluble Li Ca Li Ca Li SO Li
Practice Determine if each of the following is soluble in water KOH AgBr CaCl2 Pb(NO3)2 PbSO4 KOH is soluble because it contains K AgBr is insoluble; most bromides are soluble, but AgBr is an exception CaCl2 is soluble; most chlorides are soluble, and CaCl2 is not an exception Pb(NO3)2 is soluble because it contains NO3 PbSO4 is insoluble; most sulfates are soluble, but PbSO4 is an exception
Solution Concentrations
Solution Concentration Qualitative Description Concentrated solutions have a large amount of solute compared to solvent. Dilute solutions have a small amount of solute compared to solvent.
Quantitative Descriptions of Solutions One method for describing a solution is to quantify the amount of solute in a given amount of solution.
Solution Concentration - Molarity Moles of solute per 1 liter of solution Used because it describes how many molecules of solute in each liter of solution Molarity = moles of solute Liters of solution mol L
How to prepare 1.000 L of a 1.000 M NaCl solution First add 1 mole of NaCl to a 1.000 liter volumetric flask
Find the molarity of a solution that has 25.5 g KBr dissolved in 1.75 L of solution. g KBr g mol mol KBr mol KBr L KBr soln = M 25.5 g KBr x 1.00 mol KBr 119.00 g KBr = 0.21429 mol KBr 0.214 mol KBr molarity, M = 1.75 L KBr soln = 0.12245 M KBr
Using Molarity in Calculations Molarity shows the relationship between the moles of solute and liters of solution. If a sugar solution concentration is 2.0 M, then 1.0 liter of solution contains 2.0 moles of sugar. 2.0 mol sugar 1.0 L soln 1.0 L soln 2.0 mol sugar Questions one might ask: What is the molarity of...? How many liters contain...? How many moles...? How many grams of...? How would I prepare...?
How many liters of 0.125 M NaOH contain 0.255 mol NaOH? mol NaOH L NaOH soln mol L moles of solute Liters of solution = Molarity 0.255 mol NaOH x 1.00 L NaOH soln = 2.04 L NaOH soln 0.125 mol NaOH
Determine the mass of CaCl2 (MM = 110.98) in 1.75 L of 1.50 M solution. L CaCl2 soln mol CaCl2 g CaCl2 mol mol L g 1.50 mol CaCl2 110.98 g CaCl2 1.75 L CaCl2 soln x x 1.00 L CaCl2 soln 1.00 mol CaCl2 = 291.32 g CaCl2
How would you prepare 250.0 ml of a 1.000 M solution CuSO4 5 H2O (MM 249.69)? How many grams of CuSO4 5 H2O are required? ml soln L soln mol CuSO4 5H2O g CuSO4 5H2O ml mol mol L L g 1.000 L soln 250.0 ml soln x x 1.000 mol CuSO4 5H2O 1000 ml soln 1.000 L soln x 249.69 g CuSO4 5H2O = 62.42 g CuSO4 5H2O 1.000 mol CuSO4 5H2O Dissolve 62.42 g of CuSO4 5H2O in enough water to total 250.0 ml
Dilution
Dilution Often, solutions are stored as concentrated stock solutions. To make solutions of lower concentrations from these stock solutions, more solvent is added. The amount of solute doesn t change, just the volume of solution. moles solute in solution 1 = moles solute in solution 2 mol mol ( ) L1 = ( ) L2 L1 L2 M1 V1 = M2 V2
What is the concentration of a solution prepared by diluting 45.0 ml of 8.25 M HNO3 to 135.0 ml? M1V1 = M2V2 M1V1 V2 = M2 mol L 8.25 ( )(45.0 ml) (135.0 ml) = 2.75 =2.75 M mol L
To what volume should you dilute 0.200 L of 15.0 M NaOH to make 3.00 M NaOH? M1V1 = M2V2 M1V1 M2 = V2 mol L 15.0 ( )(0.200 L) mol L ( 3.00 ) = 1.00 L
How would you prepare 200.0 ml of 0.25 M NaCl solution from a 2.0 M solution? M1V1 = M2V2 M2V2 M1 = V1 mol L 0.25 ( )(0.200 L) mol L ( 2.0 ) = 0.025 L Dilute 25 ml of 2.0 M stock solution up to 200.0 ml.
You have a bottle of 1 molar stock solution But you WANT a 1 millimolar solution. What will you do? It s a snap I ll add 1.00 ml of the stock solution to 999 ml of water. But we only need 100 microliters of the solution Do you have any idea how much it would cost to dispose of a liter of that stuff? It s toxic What will save your job? SERIAL DILUTION will
Serial Dilution 1.00 ml 1.00 ml 1.00 ml 1.00 ml + 9.00 ml water + 9.00 ml water + 9.00 ml water + 9.00 ml water stock solution 1.00 M 0.100 M 0.0100 M 0.00100 M 0.000100 M
Solution Stoichiometry
Solution Stoichiometry Because molarity relates the moles of solute to the liters of solution, it can be used to convert between amount of reactants and/or products in a chemical reaction. Liters of a Solution of A Moles of A Moles of B Liters of a Solution of B mol L M coefficients mol L M
What volume of 0.150 M KCl is required to completely react with 0.150 L of 0.175 M Pb(NO3)2 in the reaction: 2 KCl(aq) + Pb(NO3)2(aq) PbCl2(s) + 2 KNO3(aq) L Pb(NO3)2 soln mol Pb(NO3)2 mol KCl L KCl soln mol mol mol L mol L 0.150 L Pb(NO3)2 soln x 0.175 mol Pb(NO3)2 x 2 mol KCl 1.00 L Pb(NO3)2 soln 1mol Pb(NO3)2 x 1.00 L KCl soln 0.150 mol KCl = 0.350 L KCl soln
43.8 ml of 0.107 M HCl is needed to neutralize 37.6 ml of " Ba(OH)2 solution. What is the molarity of the base?" 2 HCl(aq) + Ba(OH)2(aq) BaCl2(aq) + 2 H2O(aq) L HCl soln mol HCl mol Ba(OH)2 mol Ba(OH)2 L Ba(OH)2 soln Molarity of Ba(OH)2 soln 0.107 mol HCl 0.0438 L HCl soln x 1.00 L HCl soln x 1 mol Ba(OH)2 2 mol HCl = 0.00234 mol Ba(OH)2 0.00234 mol Ba(OH)2 0.0376 L Ba(OH)2 soln = 0.0623 M Ba(OH)2
The Big Picture of Stoichiometry Grams of A Grams of B Molar Mass Liters of a Solution of A M Moles of A Mole to Mole Ratio* Moles of B M Liters of a Solution of B Avogadro s Number Particles of A Particles of B *from balanced equation