Chapter 15 Section 15.2

1. Chapter 15Section 15.2 Homogeneous Aqueous Systems

2. Think-Pair-Share • Explain why you must be extremely careful when using electricity near a swimming pool.

3. Solutions • Aqueous Solution-Water that contains a dissolved substance. • 2 Parts to a solution: • Present in the smallest amount - Solute • Solvent - Present in the larger amount • Solvent dissolves the Solute.

4. Solutions • Are Solvents and Solutes found in the liquid state only? • Gas Solutions • The air we breathe- Oxygen and Nitrogen • Carbon Dioxide mixed with your liquid soda • Solid Solutions • Nickel Coin- Copper and Nickel • Sterling Silver- Silver and Copper • Can you name any?

5. Solutions • Homogeneous mixtures- nothing settles out when left standing • Solute particles are very…very small. • Less than 1nm = 10 -9 m • What would happen if we tried to filter a homogeneous solution through filter paper? Could you separate the solute from the solvent?

6. Solutions • Substances that dissolve most readily in water are… • Ionic Compounds • Polar Covalent Compounds • Polar molecules dissolve in Polar molecules. • Nonpolar covalent molecules such as oils, fuels, and grease dissolve in Nonpolar covalent molecules.

7. The Solution Process • A water molecule is polar, with a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. • As individual solute ions break away from the crystal, the negatively and positively charged ions become surrounded by solvent molecules and the ionic crystal dissolves.

8. The Solution Process • The process by which the positive and negative ions of an ionic solid become surrounded by solvent molecules is called solvation.

9. This relationship can be summed up in the expression “like dissolves like.” • Why is the oil and water not mixing? • Can oil and gasoline mix?

10. Electrolytes • An electrolyte is a compound that conducts an electric current when it is in an aqueous solution or in the molten state. • All ionic compounds are electrolytes because they dissociate into ions.

11. In order for the bulb to light, an electric current must flow between the two electrodes that are immersed in the solution • Sodium chloride, a strong electrolyte, is nearly 100% dissociated into ions in water.

12. Glucose, a nonelectrolyte, does not dissociate in water. • A nonelectrolyte is a compound that does not conduct an electric current in either an aqueous solution or the molten state.

13. Electrolytes • Not all electrolytes conduct electric current to the same degree • In a solution that contains a strong electrolyte, all or nearly all of the solute exists as ions. Ex: Sodium Chloride • A weak electrolyte conducts an electric current poorly because only a fraction of the solute in the solution exists as ions. • Ex: Acetic Acid

14. Your cells use electrolytes, such as sodium and potassium ions, to carry electrical impulses across themselves and to other cells • An electrolyte imbalance can occur if you become dehydrated. • When you exercise, you can lose water and electrolytes from your body through perspiration.

15. Pickles contain table salt. Why can electric current flow through a pickle, causing it to glow? • Electrolytes conduct an electric current when they are in an aqueous solution. Table salt, or NaCl, is a strong electrolyte. The water and salt in the pickle form a solution that conducts an electric current. The electric current causes the pickle to glow.

16. Explain why you must be extremely careful when using electricity near a swimming pool. • The chlorinated water in a swimming pool is a solution that can conduct an electric current. If a current is introduced into the water, any swimmers could be shocked.

17. Why do appliances warn you not to use them near water? • Because there are electrolytes in tap water and therefore it conducts electricity.

18. Thumbs Up…Thumbs Down • All Solutions are conductors of electricity. • Degree of electrical conductivity is directly related to kinetic energy. • Ionic compounds conduct electricity because they contain ions.

19. Hydrates • A compound that contains water of hydration is called a hydrate. • The dot is not a multiplication sign. • It connects the compound to however many water molecules are present.

20. Hydrates The forces holding the water molecules in hydrates are not very strong, so the water is easily lost and regained.

21. A piece of filter paper that has been dipped in an aqueous solution of cobalt(II) chloride and then dried is blue in color (anhydrous CoCl2). • When the paper is exposed to moist air, it turns pink because of the formation of the hydrate cobalt(II) chloride hexahydrate (CoCl2.6H2O).

22. Let’s test our knowledge… • Pg. 510 #49 • Pg. 281 Chart 9.4

23. To determine what percent by mass of a hydrate is water: • First determine the mass of water in one mole of hydrate. • Then determine the molar mass of the hydrate. • The percent by mass of water can be calculated using the following equation:

24. Finding the Percent by Mass of Water in a Hydrate • Pg. 500 #8 • Analyze -List the known and the unknown • To determine the percent by mass, divide the mass of water in one mole of the hydrate by the molar mass of the hydrate and multiply by 100%.

25. Let’s test our knowledge… • Pg. 512 #89 d and e

26. Calculate the percent by mass of water in epsom salt, magnesium sulfate heptahydrate (MgSO4.7H2O)

27. Test our Knowledge… • What property of all ionic compounds make them electrolytes? • Why do hydrates easily lose water when heated and regain water when exposed to moisture? • Identify the solvent and the solute in vinegar, a dilute aqueous solution of acetic acid.

28. Due Friday • Online assignment calculating % by mass.