Chapter 15Section 15.2

Homogeneous Aqueous Systems

Think-Pair-ShareO Explain why you must be extremely

careful when using electricity near a swimming pool.

SolutionsO Aqueous Solution-Water that

contains a dissolved substance. O 2 Parts to a solution:

O Present in the smallest amount - Solute

O Solvent - Present in the larger amountO Solvent dissolves the Solute.

SolutionsO Are Solvents and Solutes found in the

liquid state only?O Gas Solutions

O The air we breathe- Oxygen and NitrogenO Carbon Dioxide mixed with your liquid soda

O Solid SolutionsO Nickel Coin- Copper and NickelO Sterling Silver- Silver and Copper

O Can you name any?

SolutionsO Homogeneous mixtures- nothing

settles out when left standing O Solute particles are very…very small.

O Less than 1nm = 10 -9 mO What would happen if we tried to

filter a homogeneous solution through filter paper? Could you separate the solute from the solvent?

SolutionsO Substances that dissolve most

readily in water are…O Ionic CompoundsO Polar Covalent Compounds

O Polar molecules dissolve in Polar molecules.

O Nonpolar covalent molecules such as oils, fuels, and grease dissolve in Nonpolar covalent molecules.

The Solution ProcessO A water molecule is polar, with a

partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms.

O 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.

The Solution ProcessO The process by which the positive

and negative ions of an ionic solid become surrounded by solvent molecules is called solvation.

O This relationship can be summed up in the expression “like dissolves like.”

O Why is the oil and water not mixing?

O Can oil and gasoline mix?

ElectrolytesO An electrolyte is a compound that

conducts an electric current when it is in an aqueous solution or in the molten state.

O All ionic compounds are electrolytes because they dissociate into ions.

O In order for the bulb to light, an electric current must flow between the two electrodes that are immersed in the solution

O Sodium chloride, a strong electrolyte, is nearly 100% dissociated into ions in water.

O Glucose, a nonelectrolyte, does not dissociate in water.

O A nonelectrolyte is a compound that does not conduct an electric current in either an aqueous solution or the molten state.

ElectrolytesO Not all electrolytes conduct electric

current to the same degreeO In a solution that contains a strong

electrolyte, all or nearly all of the solute exists as ions. Ex: Sodium Chloride

O A weak electrolyte conducts an electric current poorly because only a fraction of the solute in the solution exists as ions.

O Ex: Acetic Acid

O Your cells use electrolytes, such as sodium and potassium ions, to carry electrical impulses across themselves and to other cells

O An electrolyte imbalance can occur if you become dehydrated.

O When you exercise, you can lose water and electrolytes from your body through perspiration.

O Pickles contain table salt. Why can electric current flow through a pickle, causing it to glow?

O 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.

O Explain why you must be extremely careful when using electricity near a swimming pool.

O 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.

OWhy do appliances warn you not to use them near water?

OBecause there are electrolytes in tap water and therefore it conducts electricity.

Thumbs Up…Thumbs DownO All Solutions are conductors of

electricity.O Degree of electrical conductivity is

directly related to kinetic energy. O Ionic compounds conduct electricity

because they contain ions.

HydratesO A compound that contains water of

hydration is called a hydrate. O The dot is not a multiplication sign. O It connects the compound to

however many water molecules are present.

HydratesThe forces holding the water

molecules in hydrates are not very strong, so the water is easily lost and

regained.

O 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).

O When the paper is exposed to moist air, it turns pink because of the formation of the hydrate cobalt(II) chloride hexahydrate (CoCl2.6H2O).

Let’s test our knowledge…

O Pg. 510 #49O Pg. 281 Chart 9.4

To determine what percent by mass of a hydrate is water: O First determine the mass of water in

one mole of hydrate.O Then determine the molar mass of

the hydrate. O The percent by mass of water can be

calculated using the following equation:

Finding the Percent by Mass of Water in a Hydrate

O Pg. 500 #8O Analyze -List the known and the

unknownO 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%.

Let’s test our knowledge…

O Pg. 512 #89 d and e

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

Test our Knowledge…O What property of all ionic compounds

make them electrolytes?O Why do hydrates easily lose water

when heated and regain water when exposed to moisture?

O Identify the solvent and the solute in vinegar, a dilute aqueous solution of acetic acid.

Due FridayO Online assignment calculating % by

mass.