Topic 7 Solutions. Solutions. Homogeneous mixture of substances in the same physical state Spread uniformly throughout Particles are evenly distributed. SOLUTIONS. homogeneous mixture (uniform composition throughout). Solute - substance being dissolved.
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Solutions • Homogeneous mixture of substances in the same physical state • Spread uniformly throughout • Particles are evenly distributed
SOLUTIONS • homogeneous mixture (uniform composition throughout) Solute - substance being dissolved Solvent - present in greater amount
Types of Solutions • gas - both solvent/solute are gases ex. Air • liquid - gas, liquid, or solid dissolved in a liquid • ex. salt water, antifreeze • Miscible – ex. Sugar and water • Immiscible – ex. Oil and water • Solids - 2 or more solids are uniformly spread out • alloy- ex. brass = Cu/Zn; steel = iron + carbon • aqueous –water is the solvent, (aq) ex. NaCl(aq)
Solute A solute is the dissolved substance in a solution. Salt in salt water Sugar in soda drinks Carbon dioxide in soda drinks Solvent A solvent is the dissolving medium in a solution. Water in salt water Water in soda
Solvation • the process of dissolving solute particles are surrounded by solvent particles First... solute particles are separated and pulled into solution Then...
Dissociation • separation of an ionic solid into aqueous ions NaCl(s) Na+(aq) + Cl–(aq)
Molecular Solvation • molecules stay intact C6H12O6(s) C6H12O6(aq)
- + - - + + acetic acid salt sugar Solvation and Conductivity Non- Electrolyte Weak Electrolyte Strong Electrolyte solute exists as ions and molecules solute exists as ions only solute exists as molecules only DISSOCIATION
Solubility • The solubility of a substance is the amount of solute that dissolves in a given quantity of a solvent at a specifiedtemperature and pressure to produce a saturated solution. • Solubility is often expressed in grams of solute per 100 g of solvent.
Dissolution of sodium Chloride Hydration
“Like Dissolves Like” • depends on the forces of attraction • Solute type nonpolar solvent polar solvent • Nonpolar soluble insoluble • Polar insoluble soluble • Ionic insoluble soluble
Factors Affecting Solubility • Temperature affects the solubility of solid, liquid, and gaseous solutes in a solvent; both temperature and pressure affect the solubility of gaseous solutes.
Solids –vs- Gases • Solids are more soluble at... • high temperatures. • Gases are more soluble at... • low temperatures & high pressures (Henry’s Law - mass of a dissolved gas in a liquid is directly proportional to the pressure of the gas).
Rate of Solution Formation • The compositions of the solvent and the solute determine whether a substance will dissolve. The factors that determine how fast a substance dissolves are • stirring (agitation) • temperature • the surface area of the dissolving particles
Solution Formation • A cube of sugar in cold tea dissolves slowly.
Solution Formation • Granulated sugar dissolves in cold water more quickly than a sugar cube, especially with stirring.
Solution Formation • Granulated sugar dissolves very quickly in hot tea.
Rate of Solution Formation • Temperature and Solution Formation • At higher temperatures, the kinetic energy of water molecules is greater than at lower temperatures, so they move faster. As a result, the solvent molecules collide with the surface of the sugar crystals more frequently and with more force.
Rate of Solution Formation • Stirring and Solution Formation • Stirring speeds up the dissolving process because fresh solvent (the water in tea) is continually brought into contact with the surface of the solute (sugar).
Rate of Solution Formation • Particle Size and Solution Formation • A spoonful of granulated sugar dissolves more quickly than a sugar cube because the smaller particles in granulated sugar expose a much greater surface area to the colliding water molecules.
Therefore… Solids tend to dissolve best when: • Heated • Stirred • Ground into small particles Gases tend to dissolve best when: • The solution is cold • Pressure is high
Solids tend to dissolve best when: Heated Stirred Ground into small particles Gases tend to dissolve best when: The solution is cold Pressure is high Therefore…
Solubility Curves • shows the dependence of solubility on temperature
UNSATURATED SOLUTION more solute dissolves SATURATED SOLUTION no more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form Solubility – the ability to dissolve in water concentration
Solubility • maximum grams of solute that will dissolve in 100 g of solvent at a given temperature • varies with temp • based on a saturated soln
Saturation • A solution that contains the maximum amount of solute in a given amount of solvent. • A saturated solution is at equilibrium • Ratedissolving = Ratecrystallization
Solubility • In a saturated solution, the rate of dissolving equals the rate of crystallization, so the total amount of dissolved solute remains constant. • NaCl(s) NaCl(aq)
Solubility • A saturated solution contains the maximum amount of solute for a given quantity of solvent at a given temperature and pressure. • An unsaturated solution contains less solute than a saturated solution at a given temperature and pressure.
Unsaturated • A solution that contains less solute than a saturated solution under existing conditions is unsaturated.
Supersaturated • A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated
Supersaturated • A supersaturated solution contains more solute than it can theoretically hold at a given temperature. • The crystallization of a supersaturated solution can be initiated if a very small crystal, called a seed crystal, of the solute is added.
Supersaturated • A supersaturated solution is clear before a seed crystal is added.
Supersaturated • Crystals begin to form in the solution immediately after the addition of a seed crystal.
Practice Question #1 1) According to Reference Table G, which compound solubility decreases most rapidly as the temperature changes from 10°C to 70°C? a) NH4Cl b) NH3 c) HCl d) KCl
Answer to problem #1 • Correct Answer Number: 2 • Explanation: See Ref. Table G. Notice the curves for choices 1 and 4 increase. Choice 2 and 3 both decrease but choice 2 (NH3) decreases more than 50 degrees, while HCl decreases only about 16 degrees.
Molarity • The concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solvent. • A dilute solution is one that contains a small amount of solute. • Aconcentratedsolution contains a large amount of solute.
Concentrations of Solutions • Water must be tested continually to ensure that the concentrations of contaminants do not exceed established limits. These contaminants include metals, pesticides, bacteria, and even the by-products of water treatment. You will learn how solution concentrations are calculated.
Quantities in Solutions • The amount of solute in a solution. • Describing Concentration • % by mass - medicated creams • % by volume - rubbing alcohol • ppm, ppb - water contaminants • molarity - used by chemists • molality - used by chemists
Molarity • Molarity (M) is the number of moles of solute dissolved in one liter of solution. • To calculate the molarity of a solution, divide the moles of solute by the volume of the solution.
Molarity • To make a 0.25 molar (0.25M) solution, first add ? mol of solute to a 0.50-L (500mL) volumetric flask half filled with distilled water.
Solve for Moles • Solute used is NaCl • We want to prepare 500 mL of a 0.25 Molar solution • Using the Molarity formula solve for moles of solute M = Moles of Solute Liters of Soln
Plug in Numbers • 0.250 mol/Liter = x moles 0.500L # of Moles = 0.250mol/liter x 0.500 L x = 0.125 moles
Convert Moles to Grams • 0.125 moles NaCl ? Grams • Use Mole Conversion Formula • Moles = given mass gfm
Plug in Numbers • 0.125 moles = x grams 58 g/mol (gfm of NaCl) X= 7.25 grams NaCl
Molarity • Add 7.25 grams of NaCl to water in flask • Swirl the flask carefully to dissolve the solute.
16.2 Molarity • Fill the flask with water exactly to the 500-mL mark.
#1: How many moles of NaOH are contained in 200 ml of 0.1M solution of NaOH? 2) Which solution is the most concentrated? a) 1 mole of solute dissolved in 1 liter of solution? b) 2 moles of solute dissolved in 3 liters of solution? c) 6 moles of solute dissolved in 4 liters of solution? d) 4 moles of solute dissolved in 8 liters of solution?