PACKET #9 Solutions Textbook: Chapter 15 Reference Table: F, G, & T regentsprep

PACKET #9 Solutions Textbook: Chapter 15 Reference Table: F, G, & T www.regentsprep.org

Let’s Review a little . . . • A solution is a homogenous mixture • homogeneous mixture of substances in the same physical state • contains atoms, ions, or molecules of one substance spread uniformly throughout a second substance When salt (NaCl) is stirred into water, the individual Na+ and Cl- ions separate and uniformly spread throughout the water, forming a solution • appears to be one substance

Solid Solutions: • A solid may be dissolved in another solid • Brass is a solution of zinc and copper • When metals are mixed together to form a solution, the result is called anALLOY

Gaseous Solutions: • Air is an example of a mixture of gases that form a solution • Although solutions exist in all three states the most common type of solution is one in which a solid or a liquid is dissolved in another liquid

Solution:a homogenous mixture made up of two or more substances. A solution is made up of a solute and a solvent. • Solute:a substance like salt or sugar that dissolves in a solvent like water. • Solvent: usually a liquid, for example water. If the solvent is water, then the solution is called an aqueous solution (aq).

Precipitate:a substance that is caused to become insoluble by heat or chemical reagent and separate out from a solution. Example: salt and water, boil, evaporate water, and the salt that remains are known as the precipitate. • Solubility: the most substance that can dissolve in the water (a solvent) at a specific temperature. Different substances react differently (TABLE G).

Dissolving • The solvent molecules have enough attraction for the solute particles to break the intermolecular forces between solute particles. • Solvent particles are attracted to the solute particles and bring the solute into the solution.

Factors Affecting the Rate of Dissolving • Three important factors that affect rate of dissolving are surface area, stirring, and temperature. SURFACE AREA: • The greater the SA, the faster the substance will dissolve. • More solute particles can come in contact with the solvent and be pulled into solution. • This is why granulated sugar will dissolve faster than a cube of sugar.

STIRRING: • Increased stirring causes a substance to dissolve faster. • More solute particles can come in contact with the solvent and be pulled into solution. • This is why people stir lemonade or iced tea mixes. TEMPERATURE: • For solids and liquids, increasing temperature increases the rate of dissolving. • This allows more solvent particles to collide with the solute.

For gases, increasing the temperature decreases the rate of dissolving. • The gas is more able to evaporate out of the solution. • This is why soda should be refrigerated and why it becomes flat if left open.

Remember . . . • “Likes dissolve in likes” • Polar solutes will only dissolve in polar solvents. • Non-polar solutes will only dissolve in non-polar solvents. Polar in PolarNon-polar in Polar

Table G: Solubility Curve HCl NH3 SO2

TABLE G: Solubility Curve, the horizontal line in the graph shows temperature, and the vertical line shows how many grams of a solute is the most that can dissolve in 100 grams of water. • The various compounds on the graph (solutes) dissolve differently at different temperature, and for a given temperature only a certain amount of the solutes can dissolve in 100 grams of water. • Some of the solutes on the graph are in solid form, and some are in gas form. • This graph represents that temperature does have an effect on solubility.

Solubility of a solid (KNO3, NaNO3) increases as temperature increases. • Solubility of a gas (NH3, HCl) decreases as temperature increases. HCl NH3 SO2

Table G: Solubility Curve • Concentrated: a large amount of solute per grams of solvent; there is a large concentration of solute. • Dilute: a small amount of solute per grams of solvent. • There are three types of solutions: • saturated • unsaturated • supersaturated

Saturated Solution • Contains the most solute that can dissolve at a given temperature. If you added anymore of the solute it would not dissolve. • When you graph the solubility of a solvent, the line on the graph represents saturated; all the lines on Table G are saturated!!! • Example: Look at KNO3 at 70°C, the maximum amount of the salt that can dissolve in 100 grams of water is about 134 grams, so the line for saturated can only hold 134 grams of KNO3.

Unsaturated Solution • Contains less solute than a saturated solution. You can still add more salt and it will dissolve. • Example: At 70°C, if you have 130 grams of KNO3, this would be an unsaturated solution because you can still add 4 grams of KNO3 before the solution is saturated.

Supersaturated Solution • This is only a temporary situation caused by slowly cooling a saturated solution. It has more solute than in a saturated solution. • A supersaturated solution is very unstable and the amount in excess can precipitate or crystallize. • Example: At 70°C, if you have 137 grams of KNO3, this would be an supersaturated solution because you have more than 134 grams of solute per 100 grams of water.

Pressure Affects Solubility • We have already learned that temperature has an affect on solubility, and that the nature of the solute/solvent has an affect on solubility (polar vs. non-polar) • Pressure also has an effect on solubility. • Pressure makes gases more soluble, and has almost no effect of liquids or solids. • Example: High pressure forces carbon dioxide gas into water to make soda; makes carbon dioxide more soluble. When you open the cap of soda, there is less pressure, the soda fizzes, and gas escapes.

Soluble or Insoluble? (Table F) Soluble Insoluble Insoluble Soluble NH4+

Ions that are soluble (have the highest concentration of dissolved ions)can conduct electricity (are electrolytes) • Ions that are insoluble (have the lowest concentration of dissolved ions) cannot conduct electricity (are non-electrolytes or poor electrolytes) • Electrical conductivity decreases when the concentration of ions decreases. • Remember that a precipitate is always considered insoluble.

Question: Are the following soluble? NaCl, AgBr, CaCO3, (NH4)2S Question: Based on Table F, which of the following saturated solutions has the lowest concentration of dissolved ions? (meaning insoluble) NaCl, MgCl2, NiCl2 or AgCl?

Be Specific . . . • Sometimes it is adequate to refer to a solution as dilute or concentrated, but dilute and concentrated are relative terms and are not precise with regards to the amount of solute involved • In most cases it is very important to know the specific amount of solute (the concentration) of a solution • There are several methods of expressing the specific concentration of a solute in a solution • You can describe the concentration of a solution by molarity, molality, percent by mass, or parts per million.

Molarity (Table T) • The molarity of a solution is the number of moles of solute in one liter of a solution. Molarity (M) = moles of solute liters of solution WARNING!!! Triple Threat: • May not give you moles (given/GFM) • May not give you liters (convert mL  L) • Liters of solution (solute + solvent; may have to add them together)

Molarity (Table T) Question: How many grams of NaCl would you need for a .5M solution? Question: How many moles of solute are contained in 200 mL of a 1M solution? Question: If you have 50 moles of a solute in 25 liters of solution, what is the molarity? • We said before that the higher the concentration of ions (more ions), the better the solution conducts electricity. When comparing a 1M solution of NaCl to a 5M of NaCl, the 5M of NaCl is a better conductor of electricity than the 1M of NaCl.

Molality • There are certain situations in which we must know how much solvent is present in a solution. • Molality is defined as the number of moles of solute dissolved in 1 kilogram of solute. Molality (m) = moles of solute Kg of solvent WARNING!!! Double Threat: • May not give you moles (given/GFM) • May not give you Kg (convert g  Kg)

Molality Question: Sucrose (table sugar) as a molar mass (GFM) of 342 grams per mole. What is the molality of a solution prepared by dissolving 34.2 grams of sucrose in 200 grams of water? Question: What is the molality of a solution prepared by dissolving 51 grams of NH3 in 2.0 kilograms of H2O?

Parts Per Million (ppm) (Table T) • A unit of concentration that expresses the mass of a solute dissolved in 1 million parts of a very diluted solution. ppm = grams of solute x 1,000,000 grams of solution WARNING!!! Triple Threat: • May not give you grams of solute (given/GFM) • May not give you grams of solution (mg  g) • Grams of solution (solute + solvent; may have to add them together)

Percent by Mass • Similar concept as percent composition (part/whole x 100). Looking to calculate the percent mass of solute in the whole solution. % Mass = grams solute x 100 grams solution WARNING!!! Triple Threat: • May not give you grams of solute (given/GFM) • May not give you grams of solution (convert mg  g) • Grams of solution (solute + solvent; may have to add them together)

Parts Per Million & % Mass Question: A CuSO4 solution contains .05g of CuSO4 in 1000g of solution. What is the concentration of the solution in parts per million? Question: What are the grams of solute required to make a 3 ppm solution when the amount of water is 150g? Question: In percent by mass, what is the concentration of 85.6g of hydrochloric acid in 356g of solution?

Parts Per Million & % Mass Question: What are the parts per million if a solution contains 75g of solute in 150g of solution? Question: 8 grams of NaCl is dissolved in 100 grams of solution, what is the percent by mass of NaCl?

Molarity by Dilution • Dilution - the process of adding more solvent to a solution. **Important** We’re not changing the number of moles, just the volume of solvent. The moles of solute are equal in the concentrated and dilute solutions. Before Dilution After Dilution

Molarity by Dilution M1V1 = M2V2 • M1 = initial concentration (molarity) • V1 = initial volume • M2 = final concentration (molarity) • V2 = final volume

Molarity by Dilution Question: A teacher wants to prepare 500. mL of 1.00 M solution of acetic acid from 17.5 M stock solution. What volume of the stock solution is required? Question: What volume of 16M sulfuric acid must be used to prepare 1.5L of a 0.10 M solution? Question: What volume of 12 M HCl must be taken to prepare 0.75 L of 0.25M HCl?

Colligative Properties Boiling Point Elevation: • Rule: The presence of a solute (salt or sugar) raises the boiling point of the solvent. • The greater the concentration of the solute, the more it raises the boiling point. • Water boils at 100°C, by adding glucose to water; it will raise the boiling point of water slightly. The greater the concentration of solute, the higher the boiling point becomes. Freezing Point Depression: • Rule: The presence of any solute (salt or sugar) lowers the freezing point of the solvent. • The freezing point of water is 0°C, by adding glucose to water it lowers the freezing point slightly. The greater the concentration of the solute, the lower the freezing point becomes. HOT GET HOTTER; COLD GET COLDER

Calculating the Freezing and Boiling Points of Solutions ∆Tb = (i)(+kb )(m) ∆Tf = (i)(-kf )(m) • ∆Tb & ∆Tf = changes in BP & FP • i – ions (in ionic  dissociation; covalent  1) • +kb & -kf = constants representing the number of degrees that the BP and FP of a solvent is raised when 1 mole of a molecular, non-volatile (does not evaporate with the solvent) solute is dissolved in 1 kilogram of the solvent • m = molality

kb = +0.513 °C/m • kf = -1.86 °C/m Question: What is the boiling point of a 2.0m solution of ethylene glycol in water at 1 atm? Question: What is the boiling point of a 2.0m aqueous solution of NaCl? Question: What is the freezing point of a 2.0m solution of ethylene glycol in water?

Review Questions 1) What is the molarity of a solution of NaOH if 2 liters of the solution contains 4 moles of NaOH? A) 2 M B) 8 M C) 80 M D) 0.5 M 2) How many moles of solute are contained in 200 milliliters of a 1 M solution? A) 1 B) 0.2 C) 200 D) 0.8 3) What is the total number of grams of NaI(s) needed to make 1.0 liter of a 0.010 M solution? A) 15 B) 0.15 C) 0.015 D) 1.5

4) At standard pressure when NaCl is added to water, the solution will have a A) lower freezing point and a lower boiling point than water B) higher freezing point and a higher boiling point than water C) higher freezing point and a lower boiling point than water D) lower freezing point and a higher boiling point than water 5) According to the Solubility Guidelines chemistry reference table, which of these compounds is the least soluble in water? A) K2CO3 B) Ca3(PO4)2 C) KC2H3O2 D) Ca(NO3)2

6) How many liters of a 0.5 M sodium hydroxide solution would contain 2 moles of solute? A) 1 L B) 2 L C) 3 L D) 4 L 7) How many grams of KOH are needed to prepare 250 milliliters of a 2.00 M solution of KOH (formula mass = 56.0)? A) 112 g B) 28.0 g C) 2.00 g D) 1.00 g 8) A solution of KCl(aq) contains 15 grams of solute in 85 grams of water. What is the concentration of the solution in percent by mass? A) 0.20% B) 2.0% C) 15% D) 6.0%

9) Based on the Solubility Curves chemistry reference table, which substance is most soluble at 60°C? A) NH3 B) KCl C) NH4Cl D) NaCl 10) A solution contains 90 grams of a salt dissolved in 100 grams of water at 10°C. The solution could be an unsaturated solution of A) KI B) KCl C) NaCl D) KNO3

Questions 11 and 12 refer to the following: The graph below represents the solubility curves for solute A and solute B. 11) Compare the solubility of solute A and solute B at 20DC and at 80DC. 12) At what temperature are solute A and solute B equally soluble in 100. grams of water?

PACKET #9 Solutions Textbook: Chapter 15 Reference Table: F, G, & T regentsprep