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Chapter 8

Chapter 8. Solutions, Acids & Bases. Formation of a Solution. Formations of a Solution involves: - one substance dissolving into another - can be a solid, liquid or gas ex. gas - gas: air liquid - gas: water in air gas - liquid: carbonated beverages

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Chapter 8

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  1. Chapter 8 Solutions, Acids & Bases

  2. Formation of a Solution • Formations of a Solution involves: - one substance dissolving into another - can be a solid, liquid or gas ex. gas - gas: air liquid - gas: water in air gas - liquid: carbonated beverages liquid - liquid: vinegar solid - liquid: sugar water solid - solid: stainless steel

  3. Parts of Solution • Two parts - solute: dissolved - solvent: does the dissolving OR what the solute is dissolved in * Can’t tell which is which? - the one that changes phase is the solute ex. salt in water - when both are in the same phase, the substance with the smaller amount ex. cream in coffee

  4. Parts of a Solution Cont. • Solvent = alcohol : tincture • Solvent = 2 + metals: alloy • Solvent = mercury: amalgam • Solvent = water: aqueous solution (universal solvent)

  5. Dissolving in Water • 3 ways - Dissociation of Ionic Compounds - solute and solvent must attract to one another, overcoming solute particle attraction and solvent particle attraction NaCl - Dispersion: at the ionic or molecular level - Molecular - C2H5OH will dissolve in water the – OH part of the water is polar and attracted to the polar part of water (physical change) - Ionization- HCl will dissolve in water. Break into ions: H+, Cl- and will be attracted to the positive and negative parts of water (chemical change)

  6. Types of Solutions • Homogenous mixture: - 2+ substances that are uniform throughout • Suspension • mixture that appears uniform while being stirred, separates into different phases when agitation stops ex. clay and water, aerosol cans, blood • Colloid - a mixture containing particles of varying sizes ex. fog, milk * Tyndall effect: scattering of light rays by particles

  7. Solubility • Max amount of solute that dissolves in a given amount of solvent at a constant temperature - generally expressed in g of solute per 100 g of solvent ex. • Soluble- dissolves • Insoluble- does not dissolve • Miscible- 2 liquids that will dissolve • Immiscible- 2 liquids that will not dissolve

  8. Describing Solutions • Saturated - contain as much solute as the solvent can hold at a given temperature - is you add more solute it will not dissolve • Unsaturated - solution that has less than the maximum amount of solute that can be dissolved - beverages: lemonade, Kool-aid • Supersaturated - solutions can more solute that it can normally hold at a given temperature (unstable)

  9. How Solutions Dissolve • Remember…..”like dissolves like” - Polar dissolves polar - Nonpolar disolves nonpolar * This is why oil and water don’t mix. Water is a polar substance and fats and oils are non-polar

  10. Factors Affecting the Rate of Solution • Rate of solution- a measure of how fat a substance dissolves • Four Factors - for solids, particle size (Increased surface area) - Stirring- increases rate - Amount of solute already dissolved - more solute dissolved, the rate decreases - Temperature- solubility curves

  11. Factors Affecting Solubility • 3 factors that affect solubility - nature of the solvent: (Polar vs. Nonpolar) - difference in the properties of the solvent and the solute - molecular structure and polarity - temperature: Solid in liquid (you’ll see this in solubility curves) - as temperature ,solubility ex. warm soda going “flat” - pressure: NO effect on solids or liquids Gases: as pressure , solubility

  12. Nature of the Solvent • Difference in the properties of the solvent and the solute - molecular structure and polarity

  13. Concentration of Solutions • Concentration of Solution - amount of solute dissolved in a specified amount of solution ex. amount of lemons in squeezed for lemonade - Dilute- less amount of solute, per amount of solvent ex: small amount of time the tea bag is left in - Concentrated - more amount of solute is dissolved ex. large amount of time the tea bag is left in • Expressed as: - percent by volume - percent by mass - Molarity

  14. Percent By Volume • Percent by volume = volume of solute x 100 volume of solvent - a way to measure the concentration of one liquid dissolved in another ex. how much “real juice” in your drink

  15. Percent By Mass • Percent by mass = mass of solute x 100 mass of solvent - more useful if solute is a solid ex. 100g of solution in sugar water, allow water to evaporate and 20 g of sugar is left the concentration of sugar in the solution is 20 % by mass

  16. Molarity • Molarity: the number of moles of a solute dissolved per Liters of solution. • Molarity = Moles of solute Liters of solution *remember a mole is the amount of a substance that contains approximately 6.022 x 1023 particles • Steps • 1st calculate molar mass of the solute • Dissolve with enough water to make a 1 L solution • Result is a 1-molar solution

  17. Molarity Problems • What is the molarity of a solution consisting of 111 g of CaCl2 dissolved in enough water to make 2.0 L of solution? • What volume of a 2.00-M solution KI in water contains 5.96 moles of solute?

  18. Molarity Answers 111 g CaCl2 x _1 mol_ = 1.00 110.98 1.00 = .50 M 2.0 2.00 M = 5.96 moles x L 5.96 moles = 2.98 L 2.00 M

  19. Properties of Acids • Identifying Acids - acid is a compound that produces hydronium ions (H3O+ ) when dissolved in water. - general properties include: - sour taste: lemons, lines, grapefruit - reactivity with metal: ex: left overs in foils - ability to produce color changes in indicators ex. blue litmus paper turns red

  20. Properties of Bases • Identifying Bases - base is a compound that produces hydroxide ions (OH-) when dissolved in water - general properties include: - bitter taste: baking chocolate, cough syrups - slippery feel: wet soap, cleaning products - color changes in indicators ex. red litmus paper will turn blue

  21. Neutralization and Salts • Neutralization: reaction between an acid and base - negative ions in an acid combine with the positive ions in a base to produce an ionic compound (salt) - hydronium ions from the acid combine with the hydroxide ions from the base to produce water - Overall production of salt and water ex. HCl + NaOH  HOH + NaCl A B Water Salt

  22. Proton Donors & Acceptors • Protons Donors - Acids: ex: H2SO4, , HCl • Protons Acceptors - Bases: ex. NaOH • Classifying Acids and Bases on acceptors/donors - by definition water is neither an acid or base - by acceptor/donor definition, water can act as either depending on what it reacts with ex.

  23. Objectives • Define pH, and relate pH to hydronium ion concentration in a solution • Distinguish between strong acids and weak acids, and between strong bases and weak bases. • Define buffer, and describe how a buffer can be prepared. • Explain how electrolytes can be classified

  24. Strength of Acids & Bases • pH Scale - measure of its hydronium ion concentration - pH of 7 is neutral - acids < 7, lower the number the more hydronium ions - Bases >7 - water is neutral at 7 ex. lemons, limes, oranges < 7 acidic milk, soaps, ammonia

  25. Strength of Acids • Strong Acids - ionize almost completely in water ex. HI, HCl, HNO3, H2SO4, HClO4 • Weak Acids - ionize only slightly in water - equilibrium favors reactants over products - weak acids can have a higher pH than a strong acid of same concentration * remember concentration and strength are different, do not assume a strong acid has a low pH. ex. HCl (strong acid) can have a pH of 6 concentrated acetic acid (weak acid) can have a pH of 3

  26. Strength of Bases • Strong Bases - ionize almost completely in water ex. NH3 • Weak Bases - ionize only slightly in water - reactants are favored in equilibrium - often used as buffers, solution that is resistant to large changes in pH - made by mixing a weak acid and its salt or a weak base and its salt ex. HF + NaF

  27. Strength of Electrolytes • Electrolyte - substance that ionizes or dissociates into ions when it dissolves in water - can conduct electricity well • Strong - strong acids due to dissociation ex. H2SO4 • Weak - strong bases due to dissociation ex. KOH, NaOH

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