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UNIT SEVEN: Earth’s Water

UNIT SEVEN: Earth’s Water. Chapter 21 Water and Solutions Chapter 22 Water Systems Chapter 23 How Water Shapes the Land. Chapter Twenty-One: Water and Solutions. 21.1 Water 21.2 Solutions 21.3 Acids, Bases, and pH. Chapter 21.2 Learning Goals.

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UNIT SEVEN: Earth’s Water

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  1. UNIT SEVEN: Earth’s Water • Chapter 21 Water and Solutions • Chapter 22 Water Systems • Chapter 23 How Water Shapes the Land

  2. Chapter Twenty-One: Water and Solutions • 21.1 Water • 21.2 Solutions • 21.3 Acids, Bases, and pH

  3. Chapter 21.2 Learning Goals • Explain how solutions are formed. • Define solubility and interpret solubility graphs. • Describe factors that affect the concentration of solutions. • Compare and contrast solubility of solid, liquid, and gaseous matter.

  4. Key Question: What is a solubility curve? Investigation 21B Solubility Curve of KNO3

  5. 21.2 Water and solutions • A solution is a mixture of two or more substances that is homogeneousat the molecular level. • Homogeneous means the particles are evenly distributed.

  6. 21.2 Water as a mixture • Muddy water is heterogeneous because it contains larger particles of soil or plant debris.

  7. 21.2 Colloids • Colloidsare mixtures, and look like solutions, but their particles are too small to settle to the bottom of their container over time. • Examples of colloids are mayonnaise, egg whites, and gelatin.

  8. 21.2 Tyndall effect • Tyndall effect is occurring if you shine a flashlight through a jar of liquid and see the light beam. • This distinguishes a colloid from a solution.

  9. 21.2 Suspensions • In a mixture called a suspensionthe particles can range widely in size. • Muddy water, will settle when it is left still for a period of time.

  10. 21.2 Types of mixtures • How can you tell the difference between a solution, a colloid and a suspension? First, try filtering it, then look for the Tyndall effect.

  11. 21.2 Water and solutions • A solution contains at least two components: a solvent, and a solute. • The solvent is the part of a mixture that is present in the greatest amount. Which of these is the solvent?

  12. 21.2 Water and solutions • When the solute particles are evenly distributed throughout the solvent, we say that the solute has dissolved.

  13. 21.2 Solubility • The term solubilitymeans the amount of solute (if any) that can be dissolved in a volume of solvent. Is there a limit for how much seltzer (solute) can dissolve in water (solvent)?

  14. 21.2 Solubility • Chalk and talc do not have solubility values. • These substances are insolublein water because they do not dissolve in water.

  15. 21.2 Solubility • A solution is saturated if it contains as much solute as the solvent can dissolve. • Any solute added in excess of the substance’s solubility will not dissolve. What will happen to any un-dissolved gas when you unscrew the cap of seltzer water?

  16. Solving Problems How much salt can dissolve in 200 mL of water at 25 °C? • Looking for: • …grams of solute • Given • … v = 200 mL; T = 25 C

  17. Solving Problems • Relationships: • Solubility table for reference • 35.9 g of salts in 100 mL water at 25 °C • Solution • …if there are 35.9 g salt/100 mL water, then • “x” g/ 200 mL water • = 71.8 g salts are need in 200 mL of water

  18. 21.2 Solubility • A solution is saturatedif it contains as much solute as the solvent can hold. • An examples of a saturated solution is air. • Air can be saturated with water. (We call it humidity!)

  19. 21.2 Solubility graphs • Solubility values for three solutes are plotted in this temperature-solubility graph.

  20. 21.2 Solubility • For something to dissolve in water, the water molecules need to break the bonds between the solute molecules. • Water dissolves each substance differently because the chemical bond strengths between atoms found in different solutes are not the same.

  21. 21.2 Equilibrium • When a solute like sugar is mixed with a solvent like water, two processes are actually going on continuously. • Molecules of solute dissolve and go into solution. • Molecules of solute come out of solution and become “un-dissolved.” • When the rate of dissolving equals the rate of coming out of solution, we say equilibriumhas been reached.

  22. 21.2 Equilibrium • When a solution is unsaturated its concentration is lower than the maximum solubility. • A supersaturated solution means there is more dissolved solute than the maximum solubility.

  23. 21.2 Solutions of gases and liquids • Some solutions have a gas as the solute. • In carbonated soda, the fizz comes from dissolved carbon dioxide gas (CO2).

  24. 21.2 Solutions of gases and liquids • When temperature increases, the solubility of gases in liquid decreases.

  25. 21.2 Solutions of gases and liquids • The variety and no. or organisms is controlled somewhat by the relationship between dissolved oxygen and temperature.

  26. 21.2 Solutions of gases and liquids • The concentration of dissolved oxygen in water is important for fish and aquatic life.

  27. 21.2 Solutions of gases and liquids • Oil and vinegar salad dressing separates because oil is not soluble in vinegar (mostly water). • Liquids that are not soluble in water may be soluble in other solvents.

  28. 21.2 Solubility rules • A set of solubility rules helps predict when an ionic compound is soluble or insoluble.

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