Solids, Liquids, and gases dissolve to form solutions. What is a solution? A mixture of 2 or more...

Solids, Liquids, and gases dissolve to form solutions. What is a solution? A mixture of 2 or more substances that are uniformly mixed with each other. What does it mean to dissolve? When one substance mixes into another and completely disappears. For example, NaCl in H 2 O.

The Solution Process In order for a solute to be dissolved in a solvent, the solute and solvent must be attracted to each other. The solute and the solvent molecules in a solution are then expanded (spread out), and able to mix with each other. In the example below, NaCl is broken apart because +/- water molecules are attracted to the +Na and the - Cl. The water breaks down the crystal, dissolving the salt.

Three types of interactions in the solution process: solvent-solvent interaction solute-solute interaction solvent-solute interaction H soln = H 1 + H 2 + H 3

Energy Changes in Solution To determine the enthalpy change, we divide the process into 3 steps. 1.Separation of solute particles. 2.Separation of solvent particles to make holes. 3.Formation of new interactions between solute and solvent.

Enthalpy Changes in Solution The enthalpy change of the overall process depends on H for each of these steps. Start End Start

Enthalpy changes during dissolution The enthalpy of solution, H soln, can be either positive or negative. H soln = H 1 + H 2 + H 3 H soln (MgSO 4 )= -91.2 kJ/mol --> exothermic H soln (NH 4 NO 3 )= 26.4 kJ/mol --> endothermic

The term solubility refers to the maximum amount of material that will dissolve in a given amount of solvent at a given temperature to produce a stable solution. Ack! What does this mean? It means how much solute (stuff) can dissolve in a solvent. It is dependant on temperature, how much solvent you have, how much solute you have, and whether or not you mix the solution.

Nature of the solute and solvent A solute is soluble when it dissolves completely in a solvent. A solute is insoluble when it cannot dissolve in a solvent. Some solutes are partially soluble, meaning only a bit dissolves while the rest remains solid.

When two liquids totally mix they are said to be miscible. An example of this would be alcohol and water. When to liquids do not mix they are said to be immiscible. An example would be oil and water:

polar dissolves polar Nonpolar dissolves nonpolar like dissolves like like dissolves like Two substances with similar intermolecular forces are likely to be soluble in each other. non-polar molecules are soluble in non-polar solvents CCl 4 in C 6 H 6 polar molecules are soluble in polar solvents C 2 H 5 OH in H 2 O ionic compounds are more soluble in polar solvents NaCl in H 2 O or NH 3 (l)

SOLUBILITY The solubility of a solute in a solvent at a particular temperature is the number of grams of the solute necessary to saturate 100 gm of the solvent at that temperature. FACTORS AFFECTING SOLUBILITY There are six main factors that control solubility of a solute. (1) Temperature ** (2) Nature of solute or solvent (3) Pressure (4) Concentration ** (5) Time (6) Mixing **

Effect of Temperature on Solubility Solubility increases when temperature goes up (most of the time). More solute dissolves in the solvent at higher temperatures. Solubility decreases when temperature goes down (most of the time). Less solute dissolves in the solvent at lower temperatures. In endothermic reactions solubility increases with the increase in temperature and vice versa. For example: solubility of potassium nitrate increases with the increase in temperature. In exothermic reactions solubility decrease with the increase in temperature. For example: solubility of calcium oxide decreases with the increase in temperature. Gases are more soluble in cold solvent than in hot solvent.

Temperature and Solutions Solubility: the maximum solute can dissolve in a given amount of solvent (in a given T). T Solubility T Crystal is formed, Solubility gas in liquid: T Solubility

Gases, however, decrease in solubility with an increase in temperature. By looking at the plot of solubilities below, you can see that most solids increase in solubility with an increase in temperature. The y-axis (dependant) is solubility: how much solute dissolves in the solvent. The x-axis (independent) is temperature. How much solute can dissolve is dependant on the temperature. Solubility Curve

Learning Check A. Why would a bottle of carbonated drink possibly burst (explode) when it is left out in the hot sun ? B. Why would fish die in water that gets too warm?

Effect of Pressure on Solubility Henry's Law states that "The amount of any given gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of that gas in contact with the liquid..." What this means for divers is that gas molecules will dissolve into the blood in proportion to the partial pressure of that gas in the lungs (as "warm-blooded" creatures, our core body temperature remains relatively constant). Henrys Law is used in breathalizers to determine how much alcohol a person has drunk.

Pressure and Solutions P Solubility (gas in liquid) Henrys law

Pressure and Solubility of Gases 12.5 The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henrys law). c = kP c is the concentration (M) of the dissolved gas P is the pressure of the gas over the solution k is a constant (mol/Latm) that depends only on temperature low P low c high P high c

Effect of Concentration: Degrees of Saturation When referring to solutions, there are three degrees of saturation unsaturated, saturated, and supersaturated. If a solution is unsaturated, the solvent is capable of dissolving more solute. When the solution is saturated, the solvent has dissolved the maximum amount of solute that it can at the given temperature. At this point we say that the solution is in a state of dynamic equilibriumthe processes of dissolving and precipitation are happening at the same rate. A supersaturated solution is one in which the solvent contains more solute than it can theoretically hold at a given temperature. Supersaturated solutions are often formed by heating a solution and dissolving more solute, then cooling the solution down slowly. These solutions are unstable and crystallize readily.

Seeding A surface on which to being crystallizing. Supersaturated solution

When a solution reaches saturation, some of the solid precipitates out and forms a solid on the bottom of the beaker. Sometimes a reaction happens when a solution is made, but one of the products is insoluble in the solvent and precipitates out. A precipitate is a solid that forms from a solution, typically because the solid is either insoluble in the solvent, or is no longer soluble.

Concentration Terms Solutions are often referred to as being concentrated or dilute. These two terms are very general. While concentrated indicates that there is a lot of solute dissolved in the solvent (perhaps the solution is near to being saturated) and dilute indicates that a small amount of solute is dissolved in the solvent, we often need to be exact with quantities in chemistry.

Effect of Time: Diffusion & Dissolving As time goes on, due to the random (Brownian) movement of the molecules, the solute will completely dissolve in the solvent.

Effect of Mixing You have done several experiments in which you were instructed to add a solute to a solvent and stir. What was the reason behind the stirring? When you stir a solute in a solution, you increase the movement of the molecules. When the molecules of the solute move more and faster, they come in higher contact with the molecules of the solution. The solution is able to attack the solute and pull it apart, dissolving the solution. Mixing causes the solute to dissolve in the solvent faster than if not mixed.

Example Calculate the molarity of a solution prepared by dissolving 20.0 g of solid NaOH in enough water to make 100 mL of solution. Explanation Convert grams to moles: Then convert mL to liters: Then divide: Molarity (M) The molarity of a solution is a measure of the number of moles of solute per liter of solution. This is the most common concentration unit used in chemistry. Lets now run through how you calculate the molarity of a solution.

Molality (m) The molality of a solution is a measure of the number of moles of solute per kilogram of solvent. The molality is dependent on the mass of the solvent in the solution. Try an example: A solution is prepared by mixing 80.0 g of sodium hydroxide (NaOH) with 500.0 g of water. Calculate the molality of this solution. Explanation Convert grams of solute to moles: Convert grams of solvent to kg: Divide:.

What is the molality of a 5.86 M ethanol (C 2 H 5 OH) solution whose density is 0.927 g/mL? m = moles of solute mass of solvent (kg) M = moles of solute liters of solution Assume 1 L of solution: 5.86 moles ethanol = 270 g ethanol 927 g of solution (1000 mL x 0.927 g/mL) mass of solvent = mass of solution mass of solute = 927 g 270 g = 657 g = 0.657 kg m = moles of solute mass of solvent (kg) = 5.86 moles C 2 H 5 OH 0.657 kg solvent = 8.92 m

Changing Molarity to Molality If we know the density of the solution, we can calculate the molality from the molarity, and vice versa.

Mass Percent (Weight Percent) The mass percent of a solution is another way of expressing its concentration. Mass percent is found by dividing the mass of the solute by the mass of the solution and multiplying by 100. A solution of NaOH that is 28% NaOH by mass contains 28 g of NaOH for each 100 g of solution. Heres the equation: Now try a problem involving the equation: A solution is prepared by mixing 5.00 g ethanol (C 2 H 5 OH) with 100.0 g water. Calculate the mass percent of ethanol in this solution. Explanation Plugging the values we were given into the mass percent equation, we get:

Convert % mass to Molarity What is the Molarity of a 95% acetic acid solution? (density = 1.049 g/mL) If you assume 1 L, that amount of solution = 1049 g 95% of the solution is acetic acid 1049 g solution x 0.95 = 997 g solute 997 g X 1 mol/60.05 g = 16.6 mol solute Since we assumed 1 L, thats 16.6 mol / 1 L or 16.6 M

Percent concentration: Weight / volume (W / V)% = Weight solute Volume of solution (mL) 100 Weight / Weight (W / W)% = Weight solute Weight of solution 100 Volume / volume (V / V)% = Volume solute (mL) Volume of solution (mL) 100

Solubility The maximum amount of solute that can dissolve in a specific amount of solvent usually 100 g. g of solute 100 g water

Learning Check At 40 C, the solubility of KBr is 80 g/100 g H 2 O. Indicate if the following solutions are (S) saturated or (U) unsaturated A. ___60 g KBr in 100 g of water at 40 C B. ___200 g KBr in 200 g of water at 40 C C. ___25 KBr in 50 g of water at 40 C

Parts per Million (ppm): Concentration ppm = g solute g solvent 10 6 Parts per billion (ppb): ppb = g solute g solvent 10 9

Dilution is the process of taking a more concentrated solution and adding water to make it less concentrated. The more concentrated solution before the dilution is performed is known as the stock solution. You can relate the concentration of the stock solution to the concentration of the diluted solution using the equation below: C 1 V 1 = C 2 V 2 where C is concentration (molarity) and V is the volume, in liters, of the solution. Try the following example using this equation. What volume of 6.0 M sulfuric acid (H2SO4) must be used to prepare 2.0 L of a 0.10 M H 2 SO 4 solution? Explanation Just plug the numbers into the formula! Be careful to read closely. C 1 V 1 = C 2 V 2 (6.0 M) (V 1 ) = (0.10 M) (2.0 L) V 1 = 0.033 L or 33 mL should be measured out and then diluted by adding enough water to make 2.00 L total volume. This should be a review!!!

Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution. Dilution Add Solvent Moles of solute before dilution (i) Moles of solute after dilution (f) = MiViMiVi MfVfMfVf =

How would you prepare 60.0 mL of 0.2 M HNO 3 from a stock solution of 4.00 M HNO 3 ? M i V i = M f V f M i = 4.00 M f = 0.200V f = 0.06 L V i = ? L V i = MfVfMfVf MiMi = 0.200 x 0.06 4.00 = 0.003 L = 3 mL 3 mL of acid + 57 mL of water= 60 mL of solution

Partial Pressure in terms of mole fraction: XAPtotal = PA ( X A = mole fraction of A) Example: If there are 3 moles of gas A, 4 moles of gas B and 5 moles of gas C in a mixture of gases and the pressure of A is found to be 2.5 atm, what is the total pressure of the sample of gases? What is the mole Fraction of Gas A in mixture I? What is the mole fraction of Gas B in mixture II?

Fractional crystallization is the separation of a mixture of substances into pure components on the basis of their differing solubilities. Suppose you have 90 g KNO 3 contaminated with 10 g NaCl. Fractional crystallization: 1.Dissolve sample in 100 mL of water at 60 0 C 2.Cool solution to 0 0 C 3.All NaCl will stay in solution (s = 34.2g/100g) 4.78 g of PURE KNO 3 will precipitate (s = 12 g/100g). 90 g 12 g = 78 g

Fractional Distillation Apparatus

Gravimetric Analysis 1.Dissolve unknown substance in water 2.React unknown with known substance to form a precipitate 3.Filter and dry precipitate 4.Weigh precipitate 5.Use chemical formula and mass of precipitate to determine amount of unknown ion

Titrations In a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete. Equivalence point the point at which the reaction is complete Indicator substance that changes color at (or near) the equivalence point Slowly add base to unknown acid UNTIL the indicator changes color

What volume of a 1.420 M NaOH solution is Required to titrate 25.00 mL of a 4.50 M H 2 SO 4 solution? WRITE THE CHEMICAL EQUATION! volume acidmoles acidmoles basevolume base H 2 SO 4 + 2NaOH 2H 2 O + Na 2 SO 4 4.50 mol H 2 SO 4 1000 mL soln x 2 mol NaOH 1 mol H 2 SO 4 x 1000 ml soln 1.420 mol NaOH x 25.00 mL = 158 mL M acid rx coef. M base

Electrolytes +- electrolyte Electrolyte: conduct an electric current. strong electrolytes: molecules dissociate completely to ions (NaCl). weak electrolytes: molecules dissociate partially to ions (CH 3 COOH). nonelectrolytes: molecules do not dissociate to ions (DI water). Ionization NaCl Na + + Cl - Na + Cl - bulb

An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity. A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity. nonelectrolyte weak electrolyte strong electrolyte

osmotic pressure Osmotic Pressure Semipermeable membrane Higher concentration Higher osmotic pressure

Osmotic Pressure (p) Osmosis is the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one. A semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules. Osmotic pressure (p) is the pressure required to stop osmosis. dilute more concentrated

Osmolarity (osmol) = M i M: molarity i: number of particles Osmolarity Osmotic pressure High P Low P Osmotic Pressure ( ) = MRT M is the molarity of the solution R is the gas constant T is the temperature (in K)

HemolysisCrenation Isotonic solution Hypotonic solutionHypertonic solution

A cell in an: isotonic solution hypotonic solution hypertonic solution

Dialysis Dilute solution

Chemistry In Action: Desalination

Freezing Point Depression The freezing point of a substance is defined as the temperature at which the vapor pressure of the solid and the liquid states of that substance are equal. If the vapor pressure of the liquid is lowered, the freezing point decreases. Why is a solutions freezing point depressed below that of a pure solvent? The answer lies in the fact that molecules cluster in order to freeze. They must be attracted to one another and have a spot in which to cluster; if they act as a solvent, solute molecules get in the way and prevent them from clustering tightly together. The more ions in solution, the greater the effect on the freezing point. We can calculate the effect of these solute particles by using the following formula: T f = K f m solute i where T f = the change in freezing point K f = molar freezing point depression constant for the substance (for water = 1.86C/m) m = molality of the solution i = number of ions in solution (this is equal to 1 for covalent compounds and is equal to the number of ions in solution for ionic compounds)

Freezing-Point Depression T f = T f T f 0 T f > T f 0 T f > 0 T f is the freezing point of the pure solvent 0 T f is the freezing point of the solution T f = K f m m is the molality of the solution K f is the molal freezing-point depression constant ( 0 C/m)

Change in Freezing Point Common Applications of Freezing Point Depression Propylene glycol Ethylene glycol deadly to small animals

At what temperature will a 5.4 molal solution of NaCl freeze? Solution T FP = K f m i T FP = (1.86 o C/molal) 5.4 m 2 T FP = (1.86 o C/molal) 5.4 m 2 T FP = 20.1 o C T FP = 20.1 o C FP = 0 20.1 = -20.1 o C FP = 0 20.1 = -20.1 o C Freezing Point Depression

Boiling Point Elevation The boiling point of a substance is the temperature at which the vapor pressure equals atmospheric pressure. Because vapor pressure is lowered by the addition of a nonvolatile solute, the boiling point is increased. Why? Since the solute particles get in the way of the solvent particles trying to escape the substance as they move around faster, it will take more energy for the vapor pressure to reach atmospheric pressure, and thus the boiling point increases. We can calculate the change in boiling point in a way thats similar to how we calculate the change in freezing point: T b = K b m solute i where K b = molar boiling point elevation constant (for water = 0.51C/m)

Boiling-Point Elevation T b = T b T b 0 T b > T b 0 T b > 0 T b is the boiling point of the pure solvent 0 T b is the boiling point of the solution T b = K b m m is the molality of the solution K b is the molal boiling-point elevation constant ( 0 C/m)

Change in Boiling Point Common Applications of Boiling Point Elevation

Now try a problem that deals with freezing point depression and boiling point elevation. Calculate the freezing point and boiling point of a solution of 100 g of ethylene glycol (C 2 H 6 O 2 ) in 900 g of water. Explanation: Calculate molality: Freezing point depression = T f = (m)(K f )(i) T f = (1.79)(1.86)(1) = 3.33C Freezing point = 0C - 3.33C = -3.33C Boiling point elevation = T b = (m)(K b )(i) T b = (1.79)(0.51)(1) = 0.91C Boiling point = 100C + 0.91C = 100.91C

What is the freezing point of a solution containing 478 g of ethylene glycol (antifreeze) in 3202 g of water? The molar mass of ethylene glycol is 62.01 g. T f = K f mi m =m = moles of solute mass of solvent (kg) = 2.41 m = 3.202 kg solvent 478 g x 1 mol 62.01 g K f water = 1.86 0 C/m T f = K f mi = 1.86 0 C/m x 2.41 m x 1 = 4.48 0 C T f = T f T f 0 T f = T f T f 0 = 0.00 0 C 4.48 0 C = -4.48 0 C

Colligative Properties of Nonelectrolyte Solutions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. Vapor-Pressure Lowering (Raoults Law) Raoults law If the solution contains only one solute: X 1 = 1 X 2 P 1 0 - P 1 = DP = X 2 P 1 0 0 = vapor pressure of pure solvent X 1 = mole fraction of the solvent X 2 = mole fraction of the solute P 1 = X 1 P 1 0

SAMPLE EXERCISE Calculation of Vapor-Pressure Lowering Glycerin (C 3 H 8 O 3 ) is a nonvolatile nonelectrolyte with a density of 1.26 g/mL at 25C. Calculate the vapor pressure at 25C of a solution made by adding 50.0 mL of glycerin to 500.0 mL of water. The vapor pressure of pure water at 25C is 23.8 torr. Solution Analyze: Our goal is to calculate the vapor pressure of a solution, given the volumes of solute and solvent and the density of the solute. Plan: We can use Raoults law to calculate the vapor pressure of a solution. The mole fraction of the solvent in the solution, X A, is the ratio of the number of moles of solvent (H 2 O) to total solution (moles C 3 H 8 O 3 + moles H 2 O). Solve: To calculate the mole fraction of water in the solution, we must determine the number of moles of C 3 H 8 O 3 and H 2 O: The vapor pressure of the solution has been lowered by 0.6 torr relative to that of pure water. We now use Raoults law to calculate the vapor pressure of water for the solution:

Colligative Properties of Nonelectrolyte Solutions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. Vapor-Pressure Lowering P 1 = X 1 P 1 0 Boiling-Point ElevationDT b = K b m Freezing-Point DepressionDT f = K f m Osmotic Pressure (p) p = MRT

Colligative Properties of Electrolyte Solutions 0.1 m NaCl solution 0.1 m Na + ions & 0.1 m Cl - ions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. 0.1 m NaCl solution0.2 m ions in solution vant Hoff factor (i) = actual number of particles in soln after dissociation number of formula units initially dissolved in soln nonelectrolytes NaCl CaCl 2 i should be 1 2 3

Which would you use for the streets of New Glarus to lower the freezing point of ice and why? Would the temperature make any difference in your decision? a)sand, SiO 2 b)Rock salt, NaCl c)Ice Melt, CaCl 2 Change in Freezing Point

Boiling-Point ElevationT b = i K b m Freezing-Point DepressionT f = i K f m Osmotic Pressure (p) p = iMRT Colligative Properties of Electrolyte Solutions

Tyndall Effect The Tyndall Effect is caused by reflection of light by very small particles in suspension in a transparent medium. It is often seen from the dust in the air when sunlight comes in through a window, or comes down through holes in clouds. It is seen when headlight beams are visible on foggy nights, and in most X-File episodes when Moulder and Sculley check out some dark place with flashlights. Tyndall effect is easily seen using a laser pointer aimed at the the mist from this ultrasonic humidifier's mist

In liquids the tyndall effect can be easily seen by using a laser pointer. If you dilute milk to where it is almost clear, or if you have any type of sol, such as colloidal silver, then the beam of the laser can be easily seen as it travels through the liquid. Tyndall effect is seen here using a laser pointer. The glass on the left contains 5 ppm of HVAC colloidal silver and the one on the right is from the tap after the bubbles have settled out.

Solids, Liquids, and gases dissolve to form solutions. What is a solution? A mixture of 2 or more...

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