GENERAL CHEMISTRY 2 QUARTER 3 Module 2 PDF

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NOTGeneral Chemistry 2Quarter 3 - Module 2Physical Properties of SolutionGovernment Property####### NOT FOR SALE Senior HighSchoolDepartment of Education ● Republic of the PhilippinesWhat I KnowMultiple Choice. Encircle the letter of the best answer from among the given choices. The following are un...

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Government Property

NOT FOR SALE

Senior High School

NOT

General Chemistry 2 Quarter 3 - Module 2 Physical Properties of Solution

Department of Education ● Republic of the Philippines

What I Know Multiple Choice. Encircle the letter of the best answer from among the given choices. 1. The following are units of concentration, except: A. Percent by Mass B. Parts per Million C. Mole Fraction D. Mole 2. It is the ratio of the mass of a solute to the mass of the solution, multiplied by 100 percent. A. Percent by Volume B. Percent by Mass C. Molality D. Molarity 3. These units of concentration are unitless, except: A. Mole Fraction B. Percent by Mass C. Molarity D. Percent by Volume 4. What is the unit of molarity? A. mol/kg C. mol/L

B. mol D. none of the above

5. What is the unit of parts per million (ppm)? A. mg/mol B. mol/mg C. mg/L D. mol/L 6. These properties depend on the collective effect of the concentration of solute particles present in a solution. A. Noncolligative Properties B. Colligative Properties C. Solute Properties D. Concentration Properties 7. These are colligative properties, except: A. Vapor Pressure Lowering B. Boiling Point Depression C. Boiling Point Elevation D. Freezing Point Depression

8. The Latin word for Colligative, coligare, means: A. Tied differently B. Tied together 2

C. Untied differently

D. Untied together

9. What is a nonvolatile solute? A. Solute that has a vapor pressure of its own B. Solute that does not have a vapor pressure of its own C. A & B D. None of the above 10. What is an electrolyte? A. A substance that can conduct electricity when dissolved in water B. A substance that does not conduct electricity when dissolved in water C. A substance that sometimes conduct electricity when dissolved in water D. A substance that can never conduct electricity when dissolved in water

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Lesson 1

Concentration Units

What I Need to Know This module discusses about the properties of solutions, solubility, and the stoichiometry of reactions in solutions. After going through this module, you are expected to 1. Use different ways of expressing concentration of solutions: percent by mass, mole fraction, molarity, molality, percent by volume, percent by mass, ppm (STEM_GC11PPIIId-f-111); 2. Perform stoichiometric calculations for reactions in solution (STEM_GC11PPIIId-f-112);

What’s New Activity 3.1.1. Find Me! Locate the words associated with concentration units in the grid. The words can be running in horizontal, vertical, and diagonal directions.

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F A H Y J K F K D K R E Y O E

A M P E R C E N T B Y M A S S

G G O H H J Y J S N O O S L J

S H S L N Y T F Q S M L E Y E

O E B G E A I J L O A A R E A

L J D I K F H E A L F R R E F

U Y C A S Q R R F V R I E A A

T T V F P O D A E E A T G I I

I I A J P G E S C N N Y B H T

O L S L M Y G F B T C S C F H

N A E T D I G H O E I G G W W

D L A V S O L U T E S O R K F

D O S J D E F A G Y M K N S F

E M U L O V Y B T N E C R E P

S N O I T A R T N E C N O C E

1. _____________________ 2. _____________________ 3. _____________________ 4. _____________________ 5. _____________________ 6. _____________________ 7. _____________________ 8. _____________________ 9. _____________________ 10. _____________________

What Is It In the previous lessons we discover the phase changes in terms of the accompanying changes in energy and forces between particles. Many chemical reactions take place between ions and molecules dissolved in water or other solvents, rather than between pure solids, liquids, or gases. Previously, we looked at the properties of gases, liquids, and solids. In this lesson, we will examine the properties of solutions, concentrating mainly 2

on the role of intermolecular forces in solubility and other physical properties of solution. Quantitative study of a solution requires knowing its concentration, that is, the amount of solute present in a given amount of solution. Several different concentration units are used by chemists, each of which has strengths as well as drawbacks. Let us examine the units of concentration: percent by mass, mole fraction, molarity, molality, percent by volume, and parts per million (ppm). Types of Concentration Units 1. Percent by Mass The percent by mass (also called percent by weight or weight percent) is the ratio of the mass of a solute to the mass of the solution, multiplied by 100 percent: Equation (1.1)

The percent by mass is a unitless number because it is a ratio of two similar quantities. Example 1.1 A sample of 0.894 grams (g) of potassium chloride (KCl) is dissolved in 54.8 grams of water. What is the percent by mass of KCl in the solution? Strategy We are given the mass of a solute dissolved in a certain amount of solvent. Hence, we can calculate the mass percent of KCl using Equation (1.1).

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Solution

We write

= 1.61% 2. Mole Fraction (X) The mole fraction of a component of a solution, say, component A, is written XA and is defined as Equation (1.2)

The mole fraction is also unitless, because it too, is a ratio of two similar quantities. Example 1.2 What is the mole fraction of the solute in a 40% by mass ethanol (C2H6O) solution in water? Strategy We are given the percentage by mass (40%) of the solute in the solution. Hence, we can calculate the mole fraction through (1) converting the concentration units based on the mass or moles of a solute and solvent or mass percentage, it is useful to assume a certain total mass of solution; (2) changing the masses of the components ethanol and water to number of moles; (3) substituting the values obtained in the formula and solve for the mole fraction of the solute ethanol, and solvent water. Solution We write (1)Assume there is exactly 100 grams of solution. Because the solution is 40% ethanol (C 2H6O), it contains 40 grams of ethanol and 60 grams of water. (2)

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(3)

The mole fraction of water can be solved using the formula:

3. Molarity (M) Molarity is defined as the number of moles of solute in 1 L of solution; that is, Equation (1.3)

Thus, the unit of molarity is mol/L.

Example 1.3 Determine the molarity of the solution with 0.124 mol of CoCl 2 in 0.654 L of solution. Strategy We are given the mole of a solute dissolved in a certain amount of solution. Hence, we can calculate the molarity of CoCl2 using Equation (1.3). Solution We write

4. Molality (m) Molality is the number of moles of solute dissolved in 1 kg (1000 g) of solvent – that is, Equation (1.4)

Thus, the unit of molality is mol/kg. 5

Example 1.4 The density of a 2.45 M aqueous solution of methanol (CH3OH) is 0.976 g/mL. What is the molality of the solution? The molar mass of methanol is 32.04 g. Strategy To calculate the molality of a solution, we need to know the number of moles of methanol and the mass of solvent in kilograms. We assume 1 L of solution, so the number of moles of methanol is 2.45 mol.

Solution Our first step is to calculate the mass of water in 1 L of the solution, using density as a conversion factor. The total mass of 1 L of a 2.45 M solution of methanol is Because this solution contains 2.45 moles of methanol, the amount of water (solvent) in the solution is The molality of the solution can be calculated by converting 898 g to 0.898 kg: 5. Percent by Volume The percent by volume is used to express the concentration of a solution when the volume of a solute and the volume of a solution are given, multiplied by 100. Equation (1.5)

The percent by volume is a unitless number because it is a ratio of two similar quantities. Example 1.5 In a solution, there is 122.4 mL solvent and 5.24 mL solute present. Find the percent by volume. 6

Strategy We are given the volume of a solute dissolved in a certain amount of solvent. Hence, we can calculate the volume percent using Equation (1.5). Solution We write

= 4.11% 6. Parts per million A concentration of a solution that contained 1 g solute and 1000000 mL solution (same as 1 mg solute and 1 L solution) would create a very small percentage concentration. Because a solution like this would be so dilute, the density of the solution is well approximated by the density of the solvent; for water, that is 1g/mL (other solvents are different case). So, after solving and converting the mL of solution into grams of solution (assuming that the solvent is water): We get (1g solute)/(1000000 g solution). Because both the solute and the solution are now expresses in terms of grams, it could now be said that the solute concentration is 1 part per million (ppm). The ppm unit can also be used in terms of volume/volume (v/v) instead. Example 1.6 A solution has a concentration og 1.24 g/L. What is its concentration in ppm? Strategy We need to convert the mass in grams into milligrams and then re-write the concentration in mg/L 7

Solution We write

What’s More Activity 3.1.2. Let’s do this! Answer the following problems. Write your full solution on your answer sheet and box the final answer. 1. Hydrogen peroxide, H2O2, is used by some water treatment systems to remove the disagreeable odor of sulfides in drinking water. An aqueous solution of H 2O2 prepared in the laboratory was found to have a concentration of 20.0% by mass. What is the mole fraction of H2O2? 2. What is the molality of a solution containing 0.75 moles of sodium hydroxide in 500 mL of water at 25℃? The density of water at 25℃ is 1 g/mL. (Hint: d=m/v) 3. A sample of 0.938 g of sodium hydroxide (NaOH) is dissolved in 60.9 g of water. What is the percent by mass of NaOH in the solution?

What I Have Learned Activity 3.1.3. Complete me! Complete the table by giving the equation and the units of concentration mentioned. UNITS OF CONCENTRATION 1. Percent by Mass 2. Molarity 3. Mole Fraction 4. Molality 5. Percent by Volume 6. Parts per Million

EQUATION

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UNIT

What I Can Do Activity 3.1.4 Give Example! Give two examples of the topics listed below that are present in everyday life. A. Solute B. Solvent C. Solution D. Concentration

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Lesson 2

Colligative Properties of Solution

What I Need to Know This module discusses about the colligative properties of electrolyte and nonelectrolyte solutions. After going through this module, you are expected to 1. Describe the effect of concentration on the colligative properties of solutions (STEM_GC11PPIIId-f-115); 2. Differentiate the colligative properties of nonelectrolyte solutions and of electrolyte solutions (STEM_GC11PPIIIdf-116).

What’s New Activity 3.2.1. Match Me! Choose the answer that best matches each of the definitions below. Write the letter of your answer on the column entitled “Match”. Definition 1 2

Match

It is a direct measure of escaping tendency of molecules. It depends on the collective effect of the concentration of solute particles

Key Terms A. Colligative Properties B. Boiling Point Elevation

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3

4

5

present in the solution. It is used to determine the reduced vapor pressure. The temperature at which the vapor pressure is 1 atm will be higher than the normal boiling point by an amount. It is the difference in temperature between the freezing point of a pure solvent and that of a solution.

C. Vapor Pressure D. Freezing Point Depression E. Vapor Pressure Lowering

F. Raoult’s Law

What Is It

In the previous lessons we discover that a solution is described in terms of concentration of one or more solutes present in it. There are some important physical properties of solution which are more directly dependent on the concentration of solute particles. Previously, we looked at the different concentration units and how they are utilized to determine the desired result. In this lesson, we will examine the properties that are called colligative (Latin, coligare – which means “tied together”) properties which mean, they depend on the collective effect of the concentration of solute particles present in the solution. These properties include: (1) vapor pressure lowering, (2) boiling point elevation, (3) freezing point depression, and (4) osmotic pressure. 11

Because of their direct relationship to the number of solute particles, the colligative properties are very useful for characterizing the nature of a solute after it is dissolved in a solvent and for determining the molar masses of substances. The latter will be discussed in the next lesson. Effect of solute concentration on the colligative properties of solutions The concentration or amount of nonvolatile solute (i.e., a solute that does not have a vapor pressure of its own) in the solution influences the colligative properties of solutions. The result will depend on the ratio between the number of solute and solvent particles in the solution and not on the solute's identity. However, it is necessary to consider whether the solute is an electrolyte or a nonelectrolyte. Effect of solute concentration on the colligative properties of solutions 1. Vapor Pressure Lowering A direct measure of the escaping capacity of molecules is vapor pressure. A pure liquid (solvent) can achieve equilibrium with its vapor in a closed container. And the pressure exerted by the vapor is called vapor pressure until the equilibrium is attained. A substance that does not have a noticeable vapor pressure is nonvolatile, whereas one that has a vapor pressure is volatile. If a liquid evaporates readily, a significant amount of the molecules would be present in the gas phase, resulting in a high vapor pressure. A surface completely filled by liquid molecules is seen on the left, some of which have evaporated and formed a vapor. On the right, a nonvolatile solute like salt or sugar has been dissolved into the solvent, having the effect of diluting the water. The addition of a non-volatile solute resulted in lowering of the solvent's vapor pressure. The lowering in vapor pressure depends on the amount of dissolved solute particles. The molecular essence of the solute is not 12

taken into consideration since the vapor pressure is simply a solvent's physical property and does not undergo a chemical reaction with the solvent and does not escape into the gas phase by itself.

Figure 1: Volatile Solvent VS Non-volatile Solute It should be remembered that the decrease in the vapor pressure of the solution in this case is directly proportional to the fraction of the volatile molecules in the oil, which is the solvent’s mole fraction. It is possible to assess this decreased vapor pressure using Raoult’s Law (1886).

Figure 2: Relationship Between Vapor Pressure and Mole Fraction of Water Where:

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Recall from the definition of mole fraction that in a twocomponent solution (a solvent and a single solute), Xsolvent = 1 – Xsolute. While the chemical nature of the solute is not a factor to consider, it is important to take into consideration whether the solute is an electrolyte or nonelectrolyte. Ionic compounds such as sodium chloride, NaCl, are strong electrolytes that dissociate into ions, resulting in a greater number of dissolved particles when they dissolve in solution. Consider two distinct equivalent concentration solutions: one is made of ionic compound NaCl, and the other is made of molecular compound glucose (C6H12O6). The equations below show what happens when these solutions dissolve: NaCl (s)

 Na+ (aq) + Cl- (aq)

C6H12O6 (s)



C6H12O6 (aq) particle

2 dissolved particles 1 dissolved

The sodium chloride, NaCl dissociates into 2 ions, while glucose does not dissociate. Thus, twice as many dissolved particles as in the case of NaCl would result in equal concentrations of each solution. In the NaCl solution (electrolyte), the vapor pressure of the solvent can be reduced twice as much as that of the solvent in the glucose (nonelectrolyte) solution. Since the salt solution surface is now filled with more solvent particles, there is less space for solvent molecules to evaporate, decreasing the solvent's water vapor pressure. 2. Boiling Point Elevation The addition of a non-volatile solute decreases the vapor pressure of the solution, so that the vapor pressure of the solution is returned to a value conforming to the pure solvent, the temperature must be increased. In fact, the temperature at which the vapor pressure is 1 atm is greater than the normal boiling point by an amount known as the boiling point elevation. 14

Figure 3 below shows the phase diagram of a solution and the effect that the lowered vapor pressure has on the boiling point of the solution compared to the solvent. In this case the

sucrose solution has a higher boiling point than the pure solvent. Since the vapor of the solution is lower, more heat must be supplied to the solution to bring its vapor pressure up to the pressure of the external atmosphere. The boiling point elevation is the difference in temperature between the boiling point of the pure solvent and that of the solution. Figure 3: The Result of Lowering the Vapor Pressure in a Solution to the Boiling Point Figure 4: Normal Boiling Point for Water (solvent) as a Function of Molality in Several Solution Containing Sucrose (a nonvolatile solute) For dilute solution, the elevation of the boiling point is directly proportional to the molal concentration of the solute:

The molal boiling point elevation constant Kb, has a specific value depending on the identity of the solvent. 3. Freezing Point Depression The freezing point of a substance is the temperature at which the solid and liquid forms can coexist indefinitely, at equilibrium. Under these conditions molecules pass between the 2 phases at equal rates because their escaping tendencies from the two phases are identical. Figure 5 below shows the phase diagram for a pure solvent and how it changes when a solute is added to it. The solute lowers the vapor pressure of the solvent resulting in a lower freezing point for the solution compared to the pure solvent. The freezing point depression is the difference in temperature between the freezing point of a pure solvent and that of a solution. On the graph, Tf represents the freezing point depression.

Figure 5: The Result of Lowering the Vapor Pressure in a Solution to the Freezing Point If a substance is applied to a solvent such as water at a given temperature, the solute-solvent interactions prohibit the solvent from entering the solid phase, causing the temperature to drop further until the solution solidifies. As a result, more energy must be removed from the solution to freeze it and the freezing point of the solution is power than that of the pure solvent. 16

The degree of the freezing point depression is directly proportional to the solution's molality. Thus: Where: – is the molal freezing point depression constant, a constant that is equal to the change in the freezing point for a 1 molal solution of a nonvolatile molecular solute – freezing point depression – molality of solute The study of colligative properties of electrolytes requires a slightly different approach than the one used for the colligative properties of nonelectrolytes. The explanation is because electrolytes dissociate in solution into ions, and thus as they dissolve, one unit of an electrolyte compound splits into two or more particles. Remember that it is the total number of solute particles that determines the colligative properties of a solution. For example, each unit of Na...