Solutions and Electrolytes Prepare for Recitation October 27th ALEKS Objective 9 due October 25th ANGEL Quiz 9 October 27th Lecture 25 October 19th Lecture 26 October 21st Lecture 27 October 24th Read Ch 18 1 18 4 5 5 11 3 11 6 Additional Preparation BLB 18 9 11 15 29 69 Packet 18 1 3 BLB 11 31 33 37 39 43 47 50 Packet 11 5 13 CH110 FA11 SAS 1 Liquids Phase Diagrams and Phase Changes KEY QUESTIONS THE BIG PICTURE What intermolecular forces are found in liquids How do we express concentration and perform calculations for dilutions What are electrolytes Remember macroscopic properties come from microscopic origins How do IMFs influence the dissolution process What types of compounds tend to be strong weak or non electrolytes By the end of Today s Lecture you should know Solutions Electrolytes CH110 FA11 SAS 2 Solutions The Basics Solution Solutions consist of a which is typically present in the amount and one or more which are dissolved and typically abundant Aqueous solutions Solutions in the environment Large concentrations Small concentrations CH110 FA11 SAS 3 Concentration Measures of Solute Abundance Mass Percent Parts per million ppm Mole Fraction Molarity M Molality m CH110 FA11 SAS 4 Dilutions and Aliquots Dilution changes the amount of present but not the number of moles of in the solution Dilution problems are easier to solve if you remember the definition of molarity M n V n MV constant M1V1 M2V2 Aliquot A serial dilution is made by diluting an aliquot to a known volume CH110 FA11 SAS 5 Practice Problems What mass of sucrose C12H22O11 is needed to make a 250 mL aqueous solution that is 0 750 M in sucrose If a 10 mL aliquot of this solution is diluted to 500 mL with water what is the concentration of sucrose in the new solution CH110 FA11 SAS 6 Electrolyte Solutions Electrolyte Strong electrolytes Ionization in solution Good conductors Weak electrolytes Ionization in solution Poor conductors Non electrolytes Ionization in solution Non conductors CH110 FA11 SAS 7 The Solution Process Dissolution of an electrolyte in water 1 2 Dissolution of a non electrolyte in water CH110 FA11 SAS 8 Review Ionic vs Molecular Compounds Ionic compound Usually composed of both metals and nonmetals but not always K2SO4 Mg NO3 2 NH4Cl Molecular compound Composed completely of nonmetals or nonmetals and metalloids HCl H2O NH3 CH110 FA11 SAS 9 Practice Problem What is the total molar concentration of ions present in a 0 025 M aqueous solution of magnesium nitrate A B C D E 0 025 M 0 050 M 0 075 M 0 100 M 0 125 M CH110 FA11 SAS 10 Identifying an Electrolyte If a compound is it is a strong electrolyte but it might be insoluble If a compound is it is an electrolyte if it is Examples of electrolytes Acids donate H aq Bases accept H aq Salts Examples of non electrolytes Alcohols Carbohydrates sugar Aldehydes ketones Examples of WEAK electrolytes Weak acids including carboxylic acids Weak bases including amines CH110 FA11 SAS 11 Is an Electrolyte Strong or Weak Assume all salts are electrolytes You need to learn the strong acids and strong bases all are electrolytes If a compound is an acid or a base but it is NOT a strong acid or base it MUST be a electrolyte CH110 FA11 SAS 12 Common Misconception It is a common misconception that all strong electrolytes are ionic compounds This is NOT TRUE Is HCl a molecular or ionic compound A Molecular B Ionic Is HCl a strong or weak acid A Strong B Weak Is HCl a strong or weak electrolyte A Strong B Weak CH110 FA11 SAS 13 Demo Electrolytes and Light Bulbs Bulb Wattage 7 5 25 40 Distilled H2O Tap H2O NaCl aq 1 M HCl aq 1M CH3COOH Sugar aq CH3OH For the bulb to light some minimum amount of current is needed Amount oc current is related to the conductivity of the solution Conductivity ability to conduct electricity is related to electrolyte strength CH110 FA11 SAS 14 Practice Problem Based on the results of the demo which one of the following is a weak electrolyte A B C D E F Distilled water NaCl aq 1M HCl aq 1M CH3COOH aq Sugar aq CH3OH aq CH110 FA11 SAS 15 Practice Problems Which one of the following is an ionic compound A B C D H2O NH4Cl CH3COOH NH3 Which of the following is are a weak electrolyte s HBr NH4Cl CH3CH2COOH NH3 CH110 FA11 SAS 16 Electrolyte Flowchart Water soluble compound molecular ionic Is it an acid strong electrolyte yes no Is it a strong acid yes Is it a molecular base no yes no strong weak weak nonelectrolyte electrolyte electrolyte electrolyte CH110 FA11 SAS 17 Practice with the Flowchart Categorize the following water soluble compounds as strong weak or nonelectrolytes Strong Weak Non HCl NaCl CH3OH CH3COOH NH3 Fe NO3 2 Ca OH 2 CH110 FA11 SAS 18 What You Should Know Solutions and Dilutions What is a homogeneous solution What is the difference between a solvent and a solute What are the commonly used units of solute concentration and how do you convert them How do you calculate the final concentration of a solute after a dilution Electrolytes What is a strong electrolyte and how do you identify one What is a weak electrolyte and how do you identify one What is a nonelectrolyte and how do you identify one How do you describe the dissolution process for electrolytes and nonelectrolytes CH110 FA11 SAS 19
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