Quizlet

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Clicker 1

  • How many molecules of sucrose (C12H22O11, molar mass = 342.30 g/mol) are contained in 14.3 mL of 0.140 M sucrose solution
    • A) 8.29 * 10^22 molecules C12H22O11
    • B) 1.21 * 10^21 molecules C12H22O11
    • C) 6.15 * 10^22 molecules C12H22O11
    • D) 1.63 * 10^23 molecules C12H22O11
    • E) 5.90 * 10^24 molecules C12H22O11

Solution Stoichiometry

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  • Molarity (moles solute/liter of solution) relates the moles of solute to the liters of solution.
    • Molarity can be used to convert between amount of reactants and/ or products in a chemical reaction when either the reactant or product is given in volume.
  • Example: 20.0 mL of 0.50 M NaCl
  • Molarity of A × Volume of A = moles A

Practice Problem: Solution Stoichiometry

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  • What volume (in L) of 0.150 M KCl solution will completely react with 0.150 L of a 0.175 M Pb(NO3)2 solution?

Clicker 2

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  • What volume of 0.244 M KCl solution is required to react exactly with 50.0 mL of 0.210 M PB(NO3)2 solution?
    • A) 97.4 mL
    • B) 116 mL
    • C) 43.0 mL
    • D) 86.1 mL
    • E) 58.1 mL

Types of Aqueous Solutions and Solubility

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  • You can’t add infinite amounts of solute to your solution
  • Consider two familiar aqueous solutions: salt water and sugar water.
    • Salt water is a homogeneous mixture of NaCl and H2O.
    • Sugar water is a homogeneous mixture of C12H22O11 and H2O.
  • How do solids such as salt and sugar dissolve in water?
    • Likes dissolve likes.
    • If your solute has roughly similar properties to your solvent, it will dissolve

What Happens When a Solute Dissolves?

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  • 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.

Charge Distribution in a Water Molecule

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  • There is an uneven distribution of electrons within the water molecule.
    • This causes the oxygen side of the molecule to have a partial negative charge (δ–) and the hydrogen side to have a partial positive charge (δ+).

Solute and Solvent Interactions in an Ionic Solution: A Salt Solution

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  • When sodium chloride is put into water, the attraction of Na+ and Cl– ions to water molecules competes with the attraction among the oppositely charged ions themselves.
    • Sodium chloride is an ionic compound (metal + nonmetal).
    • Ionic compounds when dissolved in water are called salt solutions.

Sodium Chloride (NaCl) Dissolving in Water

  • Each ion is attracted to the surrounding water molecules and pulled off and away from the crystal.
  • When it enters the solution, the ion is surrounded by water molecules, insulating it from other ions.
  • The result is a solution with free moving charged particles able to conduct electricity.

Electrolyte and Nonelectrolyte Solutions

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  • 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.
  • A solution of salt (an electrolyte) conducts electrical current. A solution of sugar (a nonelectrolyte) does not.

Salt versus Sugar Dissolved in Water NaCl solution Sugar–water solution

Electrolyte Solutions: What Are They?

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  • Electrolytes are classified by how they dissolve in water.
    • If their dissociation is into ions:
      • Strong electrolytes
        • Completely dissociate into ions
        • Example: CaCl2(s) → Ca2+ + 2 Cl−
      • Weak electrolytes
        • Partial dissociation into their ions
        • Example: HCOOH(aq) H+ + HCOO−
    • Molecular compounds that dissolve in water but do not form ions when they go into solution are called nonelectrolytes.

Electrolyte Solutions: Strong and Weak

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  • Ionic substances such as sodium chloride (NaCl) that completely dissociate into ions when they dissolve in water are strong electrolytes.
  • Acids are compounds that when dissolved in water dissociate to give H+
  • Bases are compounds that when dissolved in water dissociate to give OH-
  • Depending on the acid or base, their dissociation in water can be complete or partial.
    • Example:
      • HCl(aq) hydrochloric acid is a strong acid.
        • It dissociates completely in water.
          • HCl would be a strong electrolyte.
      • Acetic acid (e.g., vinegar) (HC2H3O2) is a weak acid—it dissociates partially in water.
        • HC2H3O2 is a weak electrolyte.

Clicker 3

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  • Which of the following will have the highest electrical conductivity?
    • A) 0.045 M Al2(SO4)3
    • B) 0.050 M (NH4)2CO3
    • C) 0.10 M NaBr
    • D) 0.10 M Kl
    • E) 0.10 M KF

Electrolyte and Nonelectrolyte Solutions

  • Sugar (C12H22O11) is a molecular compound.
    • Most molecular compounds (except for acids and bases) dissolve in water as intact molecules.
    • Nonelectrolyte solution

Electrolytic Properties of Solution

The Solubility of Ionic Compounds

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  • When an ionic compound dissolves in water, the resulting solution contains:
    • Not the intact ionic compound itself, but its component ions dissolved in water
  • NOT all ionic compounds dissolve in water.
    • Example:
      • If we add AgCl to water, for example, it remains solid and appears as a white powder at the bottom of the water.
  • In general, a compound is termed soluble if it dissolves in water and insoluble if it does not.

Solubility of Salts

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  • If solid silver nitrate (AgNO3) is added to water, it dissolves and forms a strong electrolyte solution.
  • Silver chloride (AgCl), on the other hand, is almost completely insoluble.
    • If solid AgCl is mixed with water, virtually all of it remains as a solid within the liquid water.

When Will a Salt Dissolve?

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  • Whether a particular compound is soluble or insoluble depends on several factors.
  • Predicting whether a compound will dissolve in water is not easy.
  • The best way to do it is to do some experiments to test whether a compound will dissolve in water, and then develop some rules based on those experimental results.

Solubility Rules

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Practice Problem: Ionic Compound Solubility

  • Predict whether each compound is soluble or insoluble
  • (a) PbCl2
  • (b) CuCl2
  • (c) Ca(NO3)2
  • (d) BaSO4

Vocab

Term Definition
electrolytes materials that dissolve in water to form a solution that will conduct electricity
nonelectrolytes materials that dissolve in water to form a solution that will not conduct electricity are called
acids compounds that when dissolved in water dissociate to give H+
bases compounds that when dissolved in water dissociate to give OH-
soluble compound which dissolves in water