Chapter 13 - Solutions

 

  1. Types of Mixtures
    1. Solutions

      soluble - definition

      dissolving sugar; sugar disappears but can be tasted; uniformly distributed in the water

      solution - definition

      same composition and properties throughout - homogeneous mixture
      1. Components of Solutions

        solvent - definition

        solute - definition

        solute sometimes is the component of the solution that is there in the lesser quantity e.g. gas in a gas or liquid in a liquid

        for a solid in a liquid, the solute particles are so small they cannot be seen and they will remain dissolved and uniformly mixed as long as the conditions do not change e.g. the solvent evaporating or the temperature changes

        figure 13-2a page 396 - filter the solution through filter paper and both solute and solvent will pass through - the solute particles are that small - 0.01 to 1 nm in diameter

        figure 13-2b page 396
      2. Types of Solution

        different types list in table 13-1 page 396 - note that you must specify which is solute and which is solvent

        figure 13-3 alloy of silver/gold

    2. Suspensions

      suspension - definition

      e.g. muddy water

      size of particles is greater than 1000 nm

      can filter the solute particles using filter paper

    3. Colloids

      colloids - definition

      particle size is between 1 nm and 1000 nm

      mud that settles out of water still leaves a cloudy mixture because a colloid has formed

      colloids pass through a paper filter

      in a colloid the particles do not settle out because of the constant movement of the surrounding molecules

      dispersed phase

      dispersing medium

      table 13-2 page 398 - examples of colloids

      foam, aerosol, gel

      Homework: 13.1
      1. Tyndall Effect

        colloids may appear homogeneous

        particles, however, are large enough to scatter light e.g. headlights on a foggy night

        Tyndall effect: need colloid, transparent medium, a strong beam of light, view the path of the light at right angle

        solution does not display this effect

        figure 13-4 page 398

        table 13-3 page 398 - properties of solutions, colloids, and suspensions

        Brownian motion - can detect motion of particle in a colloid under a microscope; view bright light across specimen at right angles; movement due to rapidly moving molecules.

    4. Solutes: Electrolytes vs. Nonelectrolytes

      solutes can be classified according to the type of particles they form in solutions: molecules/atoms or ions

      ionic compound

      electrolyte - definition

      includes soluble ionic compounds and some polar covalent compounds, e.g. HCl produces H3O+ + Cl-

      solution with neutral covalent molecules does not conduct electricity and is called an nonelectrolyte

      nonelectrolyte - definition

      figure 13-5a page 400

      figure 13-5b page 400

      figure 13-5c page 400

      not all electrolytes conduct to the same extent

      Homework: 13.2

  2. The Solution Process

    1. Factors Affecting the Rate of Dissolution
      1. Increasing the Surface Area of the Solute

        molecules or ions of the solute are attracted by the solvent and the dissolving process occurs at the surface of the solute e.g. cube of sugar in warm water

        the more surface area the faster the dissolving process

        figure 13-6 page 401
      2. Agitating a Solution

        Stirring or shaking brings the solute and solvent into better contact and increases the rate of dissolving

      3. Heating a Solvent

        at higher temperatures the average K.E. of the solvent increases and the collisions between solute and solvent are more frequent and, thus, the rate of dissolving increases for most solvents.

        Homework: 13.3
    2. Solubility

      When you add solute to solvent you eventually reach a point at which no more solute will dissolve in the solvent and the excess falls to the bottom of the container -- you have exceeded the solubility of the solvent.

      When you have reached the solubility of the solvent you can have solution equilibrium -- saturated solution.

      solution equilibrium - definition

      the solubility of the solvent and therefore where solution equilibrium occurs depends on
      a) the nature of the solvent; b) the nature of the solute; c) the temperature.
      1. Saturated vs. Unsaturated Solutions

        saturated solution - definition

        figure 13-7 page 402

        unsaturated solution - definition

        figure 13-8 page 403

        adding more solute to a saturated solution

        adding more solvent to a saturated solution

        how do you recognize a saturated solution?

      2. Supersaturated Solutions

        Saturating a solution at a temperature above room temperature and cooling it to room temperature -- what would you expect to happen?

        supersaturated solution - definition

        disturbing a supersaturated solution and the results

        seeding a supersaturated solution

      3. Solubility Values

        solubility - definition

        units are usually grams of solute/100 grams of water (or solvent)

        temperature dependent for all solutions

        for gases need pressure also

        Table 13-4 page 404

        rate of dissolving is not related to solubility

    3. Solute-Solvent Interactions

      like dissolves like
      bonding and polarity
      intermolecular forces between solute and solvent
      1. Dissolving Ionic Compounds in Aqueous Solution

        water is polar vs. ionic compounds

        solvent pulls and surround solute therefore need attraction between the two

        hydration - definition

        figure 13-9 page 405

        solute is said to be hydrated

        solvation

        hydrates (water of hydration) e.g. copper (II) sulfate penta hydrate

        figure 13-10 page 405

        water molecule is incorporated into the crystal structure

        heating gently drives off the water and leaves you with the anhydrous form of the compound

      2. Nonpolar Solvents

        ionic compounds and nonpolar solvents e.g. carbon tetrachloride and benzene and toluene

      3. Liquid Solutes and Solvents

        immiscible - definition

        toluene and water

        figure 13-11 page 406

        miscible - definition

        e.g. benzene and carbon tetrachloride - nonpolar

        e.g. ethanol and water - polar

        figure 13-12 page 406

        ethanol is intermediate between water and carbon tetrachloride

      4. Effects of Pressure on Solubility

        only important in dealing with gases

        gas + solvent = solution

        if equilibrium is undisturbed, the solubility of the gas in the liquid is unchanged at a given temperature

        increasing the pressure increases the solubility of the gas in the solvent e.g. carbonated beverages

        new equilibrium is established with more gas molecules dissolved in the solvent

      5. Henry's Law

        Henry's Law - statement

        assumption is that the gases do not react with each other; each gas would dissolve to the same extent as if it were the only gas present

        effervescence - definition

        figure 13-13 page 407

      6. Effects of Temperature on Solubility

        for gases, increasing the temperature generally decreases the solubility

        figure 13-14 page 408

        at new equilibrium have fewer gas molecules in solution

        for solids in liquids - can be either an increase or decrease in solubility

        figure 13-15 page 408

        each substance is affected differently by a change in temperature

        Homework: 13.4
    4. Heats of Solution

      always have an energy change when a solution is formed

      KI in water - outside of the container feels cold

      LiCl in water - outside of the container feels hot

      energy is required to separate solute molecules and solvent molecules and energy is involved when the solvent surrounds the solute particles - 3 energy factors in the dissolving process

      solvated - definition

      figure 13-9 page 405

      figure 13-16 page 409 Solvation process

      heat of solution - definition

      sign convention - tables only

      table 13-5 page 410

      Homework: 13.5
  3. Concentrations of Solutions

    concentration - definition

    molarity and molality

    dilute vs concentrated

    not related to saturation of solution
    1. Molarity
      molarity - definition
    2. need to know molar mass to calculate molarity
    3. symbol is M
    4. M= amount of solute in moles/volume of solution in liters
    5. use volumetric flask to prepare molar solutions
    6. figure 13-17 page 413
    7. for NaOH the molar mass is 40 g/mol
    8. thus 40 g ( one mole ) of NaOH added to a one liter volumetric flask and then add enough water to bring the total volume to one liter ---> 1 M solution ( 1 mol/1L = 1 M )
    9. OR 20 g ( 0.5 mole ) of NaOH added to a one-half liter volumetric flask and then add enough water to bring the total volume to one-half liter ---> 1 M solution ( 0.5 mol/0.5 L = 1 M )
    10. OR 20 g ( 0.5 mole ) of NaOH added to a one liter volumetric flask and then add enough water to bring the total volume to one liter ---> 0.5 M solution ( 0.5 mol/1 L = 0.5 M )
        1. First type of molarity problem - given grams and volume and asked to calculate molarity:
          Sample Problem 13-1

        2. Second type of molarity problem


          Homework: 13.6

      1. Molality
        molality - definition

        figure 13-18 page 416

        For NaOH, molar mass is 40 g;
        40 g of NaOH added to exactly 1 kg of water produces a 1 molal ( 1 m ) solution of NaOH.

        molality = moles of solute/1kg of solvent or
        molality = moles of solute/1000 g of solvent

        e.g. 80 g of NaOH dissolved in 1 kg of water would produce a 2 m solution -- 80 g of NaOH is 2 mol of NaOH in 1 kg of water is 2 mol/kg or 2m

        Sample Problem 13-4



        Sample Problem 13-5



        Homework: 13.7

        end of notes


    Molality is the concentration of a solution expressed in moles of solute per kilogram of solvent.

    Soluble means capable of being dissolved. back


















    A solution is a homogeneous mixture of two or more substances in a single phase. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The solvent is the dissolving medium in a solution. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The solute is the substance dissolved in the solution. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A suspension is a mixture in which the particles of the solvent are so large that they settle out unless the mixture is constantly stirred or agitated. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A colloid or a colloidal dispersion is a mixture that contains particles that are intermediate in size between those in solutions and suspensions. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

An electrolyte is a substance that dissolves in water to give a solution that conducts electric current. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A nonelectrolyte is a substance that dissolves in water to give a solution that does not conduct an electric current. Back














 

 

 

 

Solution equilibrium is the physical state in which the opposing processes of dissolution and crystallization of a solute occur at equal rates. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A saturated solution is a solution that contains the maximum amount of dissolved solute. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

An unsaturated solution is a solution that contains less solute than a saturated solution under the existing conditions. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A supersaturated solution is a solution that contains more dissolved solute than a saturated solution contains under the same conditions. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Solubility of a substance is the amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature. Back



















 

 

Hydration is the solution process with water as the solvent. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Immiscible indicates that liquid solutes and solvents are not soluble in each other. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Miscible indicates that liquid solutes and solvents freely dissolve in one another in any proportion. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Henry's law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Effervescence is the rapid escape of a gas from a liquid in which it is dissolved. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Solvated means that a solute particle is surrounded by solvent molecules. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Heat of solution is the amount of heat energy absorbed or released when a specific amount of solute dissolves in a solvent. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The concentration of a solution is a measure of the amount of solute in a given amount of solvent or solution. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Molarity is the number of moles of solute in one liter of solution. Back