Water and Aqueous Solutions

Solvents, Solutes, and Solutions

Natural Water

• Water is never pure in nature, there are always impurities… Why??

• Because water dissolves and dissociates so many things, there are always “extras” in the aqueous system

What is a Solution?

• Solutions are homogeneous and contain a – Solute (which is the thing being dissolved) AND A – Solvent (the thing doing the dissolving)

• These particles in solution are very tiny and therefore do not settle back out.

• They also do not separate through a filter!!

Solubilities of Solids

• The greater the surface area, the faster the dissolving process.

• Dissolving only takes place at the surface of substances. The solvent cannot penetrate the solute, which make it take longer to dissolve bigger “chunks”

• Shaking will also increase the speed. Why?

Temperature

• Solubilities of solids generally increase with temperature.

• Increasing the temperature increases the speed of the molecules which increases the number of collisions. This speeds up the solvent’s ability to dissolve the solute.

Solubility and Polarity

• “Like dissolves Like” … meaning _________________

• Miscible – describes two or more liquids that are able to dissolve into each other in various proportions.

• If two substances are immiscible, than they will not mix together.

Likes Dissolve Likes• Water is POLAR!!!– Meaning it has a (+) side and a (-) side– This property enables it to surround and dissolve (or

dissociate) a large range of other polar substances

• Water will ONLY dissolve other POLAR things

• If I want to dissolve a nonpolar substance into a solvent what should I use? ______________

Ionic Dissociation

• The (+ H) end of water will tear off the ______ end of the salts and the (- O) side will _______ _____________________________________.

• After this “break down” you have free-floating ions in solution… this is now able to carry a charge or is _____________________.

Concept Check

• Why is ethanol miscible in water?

• Why do sugar cubes dissolve more slowly in water than granulated sugar?

• What factors are involved in determining the solubility of an ionic salt?

• You keep adding sugar to a cold cup of coffee. You stir it by eventually you notice sugar on the bottom. Explain why no more sugar dissolves.

Conductivity

• Some substances have the ability to conduct an electric current. This depends on whether or not it contains charged particles that are able to move freely around the solution.

• An electrolyte is a substance that dissolves in water to give the solution the ability to conduct an electric current.

Conductivity

• A nonelectrolyte is a liquid or solid substance that does not allow the flow of an electric current, either in solution or in its pure state, such as water or sucrose.

• Ionic salts dissociate into their individual charged ions that move around the solution freely. Would this be an electrolyte or a nonelectrolyte?

Water of Hydration

• Some crystals need the H2O molecules to hold it all in place and stay stable.

• A compound that has water holding it together is know as a hydrated compound.

• How could you determine how much water is in a hydrated compound????

Hydrated Compounds

CuSO4 * 5H2O

Heterogeneous Mixtures

• Suspensions – mixtures that the particles settle out after left to sit.– Example: clay in water or milk sitting

• Colloids – particle size is between that of suspensions and true solutions– Example: aerosol sprays and smoke

Tyndall Effect• Colloidal particles

exhibit the Tyndall Effect – The scattering of

light in all directions

• Think about a really foggy day with your headlights

Emulsions

• Emulsions are colloidal dispersions of liquids in liquids

• Soap and detergents are emulsifying agents because they help to “take into solution” (kind of) the oils and grease stains

Concept Check… Again

• Sea water is a great conductor. Why?

• Tap water is also very good because it is not distilled (still contains ions and minerals).– Do not use electrical devices by water

End of Water

Exam is coming up… Study all vocab and sections!!