Chemistry Chapter 7

•Which of the following is true for a colloid? 1.The path of a beam of light through a colloid is visible 2.Dispersed phase particles can be seen 3.The influence of gravity will separate a colloid 4.More than one statement is true •

1

•Which of the following is NOT a characteristic of a solution? 1.It will separate while standing 2.It has uniform composition 3.It cannot be separated by filtration 4.It can be separated into pure components

1. It will separate while standing

•What is the boiling point of a 0.250 M NaOH (aq) solution? (The Kb for water is 0.52°C/M) 1.0.13°C 2.99.74°C 3.100.26°C 4.100.39°C •

100.26

Heat and Solution Formation

Endothermic: solute+solvent+heat=solution Exothermic: Solute+solvent+solution+heat

•Which of the following does not experience the Tyndall effect? 1.Fog 2.Serum 3.Smoke 4.Salt water

Salt water

Solution Stoichiometry Example (continued)

•According to the reaction, 1 mole of NaOH reacts with 1 mole of HCl, so 0.00313 moles of HCl will be needed •Volume of 0.100 M HCl solution that contains 0.00313 can be calculated by dividing the needed number of moles by the solution molarity: • • • • • •Thus, it is seen that 0.0313 liters or 31.3 mL of 0.100 M HCl solution will be required to react with the 25.00 mL of 0.125 M NaOH solution

Formation and Destruction of Colloids (continued)

•As smoke passes over the charged surfaces, the colloid particles lose their charges •Particles then coalesce into larger particles that settle out and are collected for disposal •Emulsifying or stabilizing agents are used to stabilize some colloids •Prevent colloids from coalescing and settling •Example - Soap/detergent ions form a charged layer around nonpolar oils and greases •Keep them separated and suspended

Osmotic Pressure of Solutions

•Can be calculated using the following equation: •π - Osmotic pressure in units •n - Number of moles of solute particles obtained when 1 mole of solute dissolves •M - Molarity of the solution •R - Universal gas constant written as 62.4 L torr/K mol •T - Solution temperature in Kelvin •Product of n and M is called the osmolarity of the solution

Solution Properties

•Conductive solutions are formed when soluble ionic materials or highly polar covalent molecules dissolve in water •Electrolyte: Solute that when dissolved in water forms a solution that conducts electricity •Nonelectrolyte: Solute that when dissolved in water forms a solution that does not conduct electricity

Solution Stoichiometry Example

•Consider the following balanced equation: • • •How many mL of 0.100 M HCl solution would exactly react with 25.00 mL of 0.125 M NaOH solution? •Solution The number of moles of NaOH in 25.00 mL of 0.125 M solution is calculated by multiplying the molarity and the solution volume in liters:

Colligative Properties of Solutions

•Depend only on the concentration of solute particles in the solution •Boiling point, freezing point, and vapor pressure are closely related colligative properties

•Which of the following is NOT a solution? 1.Air 2.Milk 3.Steel 4.Tap water

Answer is milk

•A separatory funnel allows liquids that are _____ to be separated 1.immiscible 2.insoluble 3.miscible 4.soluble •

1. immiscible

•Based on the interaction of water, carbon tetrachloride, and iodine in the video clip, which of the following is more likely to dissolve in water than in carbon tetrachloride? 1.NaCl 2.CO2 3.F2 4.More than one answer is correct

1.NaCl

•When ethanol is dissolved in water, the _____ are hydrated 1.atoms 2.anions 3.cations 4.molecules

4. molecules

•If carbon dioxide, sodium chloride, and glucose are dissolved in water, what is the specific term that describes the water? 1.Solution 2.Solute 3.Solubility 4.Solvent

4.Solvent

•During osmosis, _____ particles flow through the semipermeable membrane to bring the two solutions closer to the same _____ 1.solute; mass 2.solvent; mass 3.solute; concentration 4.solvent; concentration

4.solvent; concentration

Solution Preparation Example 1

•Describe how to prepare 500 mL of 0.250 M NaCl solution •Solution •Mass of the required amount of NaCl must be determined first •Volume and concentration of the desired solution are known, so the equation for molarity is rearranged to solve for the number of moles of solute needed •The result is: Moles of solute=M x Liters if solution =0.250 M x 0.500L=0.125 mole

Solution Preparation- method 2

•Diluting a concentrated solution with solvent to produce a solution of lower concentration •Number of moles of solute taken from the concentrated solution and diluted with water is the same as the number of moles of solute in the resulting dilute solution •Subscript c and d refer to more concentrated and dilute solutions, respectively •C represents any appropriate concentration

Colloids

•Homogeneous mixtures of two or more components in which there is more of one component than of the others •Dispersing medium: Substance present in a colloidal dispersion in the largest amount •Analogous to the solvent of a solution •Dispersed phase: Substance present in a colloidal dispersion in amounts less than the amount of the dispersing medium •Analogous to the solute of a solution •Particles: •Cannot be seen •Do not settle under the influence of gravity •Scatter and reflect light

Solutions

•Homogeneous mixtures of two or more substances in which the components are present as atoms, molecules, or ions •Can be colored and are transparent (clear) •Particles in liquid solutions are: •Too small to reflect light •In constant motion and do not settle under the influence of gravity •Physical state of a solution is often the same as the physical state of the solvent

The Solution Process

•Involves interactions between solvent molecules (often water) and solute particles •Effective rule of thumb for solubility - Like dissolves like •Polar solvents dissolve polar or ionic solutes •Nonpolar solvents dissolve nonpolar or non-ionic solutes •Solute will not dissolve in a solvent if: •Forces between solute particles are too strong to be overcome by interactions with solvent particles •Solvent particles are more strongly attracted to each other than to solute particles

Formation and Destruction of Colloids

•Ions in a dispersing medium are attracted to colloid particles and stick on their surfaces •All colloid particles within a particular system will attract ions of only one charge or the other •Colloid particles all acquire the same charge and repel each other •Prevents particles from coalescing into aggregates large enough to settle out •Cottrel precipitator •Removes colloid solids from gaseous smokestack wastes before they are released into the atmosphere •Contains a number of highly charged plates or electrodes •

Solubility

•Maximum amount of solute that can be dissolved in a specific amount of solvent under specific conditions of temperature and pressure •Soluble substance: Dissolves to a significant extent in a solvent •Insoluble substance: Does not dissolve to a significant extent in a solvent •Immiscible: Liquids that are insoluble in each other •In gases, solubility is: •Inversely proportional to temperature •Directly proportional to pressure of the gas above the solution at constant pressure

Solution Preparation- Method 1

•Mixing together proper amounts of solute and solvent •When concentration is based on solution volume, a volumetric flask is used •When concentration is based on solvent mass, the correct mass of solvent is added

Solution Stoichiometry

•Number of moles of solute in a volume of solution of known molarity can be obtained by multiplying the known molarity with the solution volume in liters •Molarity - Ratio of moles of solute to liters of solution •Can be written as two conversion factors • • • •Equation on the left - Used to multiply by the molarity and is selected to cancel the units of liters of solution and obtain the units of moles of solute •Equation on the right - Used to divide by the molarity and is selected to cancel the units of moles of solute and obtain the units of liters of solution

Osmosis and Osmotic Pressure

•Osmosis: Process in which solvent molecules flow through a semipermeable membrane into a solution •Net flow of solvent is always from the more dilute to the more concentrated solution •Osmotic pressure: Hydrostatic pressure that is required to prevent the net flow of solvent through a semipermeable membrane into a solution

The Tyndall Effect

•Path of a beam of light through a colloid is visible because the light is scattered

Dialysis

•Process in which solvent molecules, other small molecules, and hydrated ions pass from a solution through a membrane •Dialyzing membrane: Semipermeable membrane with larger pores than osmotic membranes •Used to: •Separate small particles from colloids •Clean the blood of people suffering from kidney malfunction

Degrees Of Saturation

•Saturated solution •Contains the maximum amount possible of dissolved solute in a stable situation under the prevailing conditions of temperature and pressure •Supersaturated solution •Unstable solution that contains an amount of solute greater than the solute solubility under the prevailing conditions of temperature and pressure •Prepared by forming a nearly saturated solution at high temperature and cooling the solution to a lower temperature

Solvent and Solute

•Solvent: Substance present in the largest amount •Solute: Any substance present in an amount less than that of the solvent •One solution may contain more than one solute •Solution forms when one or more solutes dissolve in a solvent

Electrolytes

•Strong electrolytes •Dissociate completely into charged ions when they dissolve •Form strongly conducting solutions •Examples - HCl and Ca(NO3)2 •Weak electrolytes •Dissociate into ions only slightly when they dissolve •Dissolve but remain in the form of uncharged molecules •Example - Acetic acid

Solution Preparation Example 1 Continued

•Thus, 0.125 moles of NaCl is needed •NaCl has a formula weight of 58.4 u, so 0.125 moles have a mass of 0.125×58.4 g or 7.30 grams •Solution is prepared by weighing a sample of NaCl with a mass of 7.30 grams •Sample is put into a 500-mL volumetric flask and pure water is added up to the mark on the flask

Types of Percentage Concentrations

•Volume/volume percent (v/v): Expresses the volume of solute contained in 100 volumes of solution •Any volume units may be used •Must be the same for both the solute and the solution

Types of Percentage Concentrations

•Weight/weight percent (w/w): Expresses the mass of solute contained in 100 mass units of solution •Any mass units may be used •Mass of solute and solution must be in the same units •Weight/volume percent (w/v): Expresses the grams of solute contained in 100 mL of solution •Solute mass must be expressed in grams, and the solution volume must be expressed in mL