Chapter 6: Solutions

This chapter will introduce the chemistry needed to understand: Section 1: Solutions & electrolytes Section 2: Concentrations of solutions Section 3: Acidity & pH

Section 1—Solutions & Electrolytes

Dissolving Substances Substances are dissolved by a process called hydration when the solvent is water The solvent and solute need to break intermolecular forces within themselves- This requires ENERGY (ENDOTHERMIC) New intermolecular forces are formed between the solvent and solute.- This releases ENERGY(EXOTHERMIC) The solvent “carries off” the solute particles

Solution Formation Endothermic Exothermic Endothermic

Dissolving Ionic Compounds + - O H - + Solute,Ionic compound Solvent,water Water molecules are polar and they are attracted to the charges of the ions in an ionic compound. - + - When the intermolecular forces are stronger between the water and the ion than the intramolecular forces between the ions, the water carries away the ion. + - + - + -

Dissolving Ionic Compounds + - O H - + Ionic compound water - As more ions are “exposed” to the water after the outer ions were “carried off”, more ions can be “carried off” as well. + - + - + - + -

DRAW THIS IN THE BOX + - O H - + Ionic compound water + - These free-floating ions in the solution allow electricity to be conducted - + - + - + -

Electrolytes When there are free-floating charges in a solution then it can conduct electricity. Substances that produce free-floating charges when dissolved in water are called electrolytes.

Dissolving Covalent Compounds: POLAR MOLECULES Solvent, water (polar) + - - + Solute, sugar (polar) Polar covalent molecules are formed in the same way—water forms intermolecular forces with the solute and “carries” the solute particles away. - + - + - +

DRAW THIS IN THE BOX Solvent, water (polar) + - - + Solute, sugar (polar) However, the polar covalent molecules stay together and just separates from other solute molecules. NO charged ions form. - +

Non-electrolytes When molecules separate from other molecules, but free-floating charges are not produced, the solution cannot conduct electricity. These are called non-electrolytes

Types of Electrolytes Strong Electrolytes Weak Electrolytes Non-Electrolytes Soluble Ionic compounds Strong Acids & Bases Insoluble Ionic Compounds Weak Acids & Bases Covalent Compounds except for ACIDS & BASES Almost all ions are separated when dissolved in water. Only a few ions are separated when dissolved in water No molecules separate—ions are not formed Easily conducts electricity when dissolved in water Conducts electricity slightly when dissolved in water Does not conduct electricity at all when dissolved in water

Breaking up Electrolytes Leave polyatomic ions in-tact (including the subscript within the polyatomic ion) All subscripts not within a polyatomic ion become coefficients Be sure to include charges on the dissociated ions! Example: Break up the following ionic compounds into their ions KNO3 Ca(NO3)2 Na2CO3

Breaking up Electrolytes Leave polyatomic ions in-tact (including the subscript within the polyatomic ion) All subscripts not within a polyatomic ion become coefficients Be sure to include charges on the dissociated ions! Example: Break up the following ionic compounds into their ions KNO3 Ca(NO3)2 Na2CO3  K+1 + NO3-1  Ca+2 + 2 NO3-1  2 Na+1 + CO3-2

Section 2: Types of Solutions A solution is made of two parts: SOLUTE: the substance that is dissolved; usually in minority SOLVENT: The substance that does the dissolving, usually in majority When 2 substances dissolve in one another, they are SOLUBLE If they cannot dissolve in one another, they are INSOLUBLE

Examples of Solutions SOLID-LIQUID LIQUID-SOLID GAS-LIQUID Salt Water Dental Filling (Mercury in Silver) SODA (Carbon dioxide gas in water)

Examples of Solutions When 2 liquids dissolve in one another, they are SOLID-SOLID LIQUID-LIQUID GAS-GAS ALLOYS (brass, bronze, sterling silver, steel) Alcohol & water Acetic acid in water(vinegar) AIR (Oxygen in Nitrogen gas) When 2 liquids dissolve in one another, they are MISCIBLE If they cannot dissolve in one another, they are IMMISCIBLE.

Types of Solutions Unsaturated Saturated Super-Saturated Has more solute dissolved than a saturated solution has at room temperature No visual- need some background information Not full- we can add solute to the solvent & it will dissolve Visual-no solid on bottom It’s “Full”- no more solute can be dissolved Visual- solid can be seen at the bottom

Diagrams of Unsaturated,Saturated, & SuperSaturated Solutions

Diagrams of Unsaturated vs Saturated Solutions

A SUPERSATURATED SOLUTION A supersaturated solution can be seeded. This is a solution at room temperature that has beyond the maximum amount of solid it can dissolve.

A SUPERSATURATED SOLUTION Crystallization Begins.

A SUPERSATURATED SOLUTION Crystallization Continues.

A SUPERSATURATED SOLUTION A SuperSautrated solution is now saturated. This is also very exothermic!

Solubility of a Gas vs Liquid In general, the higher the temperature of a solution, more solid can be dissolved. the higher the temperature of a solution, less gas can dissolve. Thermal Pollution!

Solubility of Gas vs Liquiud

Henry’s Law As the pressure above a liquid increases, the solubility of a gas within a liquid will increase

Reading a Solubility Curve Find the data point on the graph of the temperature and solubility of solute in solvent. If it is below the line, it is UNSATURATED IF it is on the line, it is SATURATED If it is above the line, the difference between the point and the line is the extra amount that is sitting at the bottom.

Reading a Solubility Curve Examples What kind of solution occurs when 40g of KCl is dissolved in 100 g H2O at 60ºC? What kind of solution occurs when 40g of KCl is dissolved in 100 g H2O at 40ºC? What is the maximum amount of NaBr that can be dissolved in 100 g H2O at 60ºC? unsaturated saturated 120 g

Reading a Solubility Curve Examples 4. What is the maximum amount of KNO3 that can be dissolved at 70ºC? 5. According to the diamond mark, How much of the KNO3 has been added to the water at 70ºC? 6. How much extra KNO3 is sitting at the bottom of the container at this temperature of 70ºC? 140g 160g 20g

Factors that Affect the Rate of Hydration 1. Temperature 2. Particle Size 3. Agitation (stirring)

Section 3: Concentration A measure of the amount of solute in a given amount of solution Qualitative Description: Dilute: small amount of solute compared to solvent Concentrated: large amount of solute compared to solvent Concentrated Dilute

Concentrated versus Dilute solvent solute Lower concentration Not as many solute (what’s being dissolved) particles Higher concentration More solute (what’s being dissolved) particles

Molarity: a quantitiative description of concentration Molarity (M) is a concentration unit that uses moles of the solute instead of the mass of the solute 2M solution is 2 moles of solute dissolved in 1.0 L of solution moles Molarity X Liters

Molarity Example Example: If you dissolve 5.0 moles of NaCl in 300.0 mL of water, what is the molarity?

Molarity Example 17 M NaCl Example: If you dissolve 5.0 moles of NaCl in 300.0 mL of water, what is the molarity? Remember to change mL to L! 300. mL of water = 0.300 L 17 M NaCl

Molarity Example Example: If you dissolve 12.0 g of NaCl in 150.0 mL of water, what is the molarity?

Molarity Example = _______ mole NaCl 1.37 M NaCl If you dissolve 12.0 g of NaCl in 150.0 mL of water, what is the molarity? Na Cl 1 22.99 g/mole 35.45 g/mole  = + 58.44 g/mole 1 mole NaCl molecules = 58.44 g 12.0 g NaCl 1 mole NaCl = _______ mole NaCl 0.205 58.44 g NaCl Remember to change mL to L! 150.0 mL of water = 0.150 L 1.37 M NaCl

Molarity Example Example: How many grams of CaCl2 would be needed to make 25.0 ml of a 2.5M solution?

Molarity Example = 6.9 grams CaCl2 .0625 moles NaCl How many grams of CaCl2 would be needed to make 25.0 ml of a 2.5M solution? Ca Cl 1 2 40.01 g/mole 35.45 g/mole  = 40.08 g/mole 70.90 g/mole + 110.98 g/mole 1 mole CaCl2 = 110.98 g .063 mol CaCl2 110.98 g CaCl2 = 6.9 grams CaCl2 1 mol CaCl2 Remember to change mL to L! 25 mL of water = 0.025 L .0625 moles NaCl

How to Make a Solution Make 500. 0 ml of a 0 How to Make a Solution Make 500.0 ml of a 0.12 M solution of CoCl22H2O 1st: Convert your moles of solute to grams. .12 M x .500L = .060 moles solute .060 moles x 165.87 g/1mol = 9.948 g (10. g) 2nd : Add solute amount to a volumetric flask. Add 10.0 g cobalt chloride to flask 3rd : Add enough solvent to make the required amount of solution and stir. In this case, the solvent is ethanol. Add slowly until 500 ml of solution is reached.

What Not to Do! Never add the solvent first!

Dilution: A technique used to make a dilute solution from a Concentrated Solution = .0050 mol .10 L = .050 M I2 = .0050 mol .50 L = .010 M I2

How to Calculate a Dilution M1V1= M2V2 moles1 = moles2 M1V1 = original(stock) concentration & volume M2V2 = new concentration & volume You do not have to change your volume to liters! Example: What is the molarity of a new solution if you diluted 100.0 ml of 3.0M HCl to 250.0 ml?

Example:. What is the molarity of a new solution if you diluted 100 Example: What is the molarity of a new solution if you diluted 100.0 ml of 3.0 M HCl to 250.0 ml? M1V1= M2V2 (3.0M)(100.0ml) = (X)(250.0 ml) 300.0 Mml= 250.0ml x 250.0 ml 250.0ml X= 1.2 M

Add 875 ml of water to 375 ml to make 1250 ml. Example: What volume would need to be added to dilute a 375 ml of a 5.0 M to 1.5 M? M1V1= M2V2 (5.0M)(375ml) = (X)(1.5M) 1875 Mml= 1.5M x 1.5 M 1.5 M X= 1250 ml Add 875 ml of water to 375 ml to make 1250 ml.