Chapter 5
Solutions!
What is a Solution?
Fill in Table on Pg. 188 #1:
A solution is a homogenous mixture of substances
composed of at least one solute dissolved in a
solvent.
Characteristics of solutions:
-Particles cannot be seen with the naked eye
-Particles cannot be separated by filtering
-Solutions are transparent
Solute vs. Solvent
Solute – The substance that is dissolved (e.g. NaCl)
Solvent – The substance that the solute is dissolved
in (e.g. Water)
Solutes and solvents may be all three phases:
Table 1 – pg. 192:
Solute in solvent Example solution Source
Gas in gas
Gas in liquid
Gas in solid
Liquid in liquid
Solid in liquid
Solid in solid
Oxygen in Nitrogen
Oxygen in water
Oxygen in ice
Methanol in water
Sugar in water
Tin in Copper
Air
Water (ocean)
Ice
Antifreeze
Syrup
Bronze alloy
Steel is a solution
(alloy) of iron in carbon,
stainless steel also
contains chromium.
In this chapter we will focus on solutions that use
water as their solvent.
Aqueous Solutions
If a solution uses water as a solvent, we call it an
aqueous solution.
We can indicate this in a chemical equation by
adding (aq).
NH3(aq) – Ammonia gas (solute) dissolved in water (solvent)
Other solvents can be shown in the same way, but
for this chapter we will deal primarily with aqueous
solutions.
Water is a very important part of
life. Many chemical reactions
require water to occur, even
though the water itself may not
react.
Acids & Bases
Acids
-have pH < 7
-turn litmus red
-ionize in water to
produce H+ ions
-conduct electricity when
in a solution
-taste sour
Bases
-have pH > 7
-turn litmus blue
-dissociate in water to
produce OH- ions
-conduct electricity when
in a solution
-taste bitter
-feel slippery
Examples:
Examples:
Hydrochloric acid - HCl(aq)
Acetic acid – CH3COOH(aq)
Sodium hydroxide - NaOH(aq)
Potassium hydroxide – KOH(aq)
Electrolytes vs. Non-electrolytes
An electrolyte is a solution that conducts electricity;
these are mostly highly soluble ionic compounds,
including acids and bases.
Molecular compounds do not usually conduct
electricity, therefore they are non-electrolytes.
*It is important to note that an ionic compound by
itself will not conduct electricity, only when it is in a
solution! (or melted)*
Video: Conductivity of compounds
http://www.youtube.com/watch?v=4FLFy3mrjD4
Video: Conductivity of molten sodium chloride
http://www.youtube.com/watch?v=NfNIn4R8tg4
Common Properties (Review)
Ionic compounds
- Metals give up electrons to non metals
- When soluble they dissociate in water into IONS
- Solutions are (mostly) neutral in pH and
conduct electricity
Molecular Compounds
- Share electrons (nonmetal and nonmetal)
- When soluble they separate in water to form
individual MOLECULES
- Solutions are neutral in pH and do not conduct
electricity
Strong Acids
- turn litmus paper red
- ionizes to produce hydrogen ions H+ in water
(not ionic compounds though)
- are electrolytes when dissolved in water
Bases
- turns litmus paper blue
- dissociates to produce hydroxide (OH-) ions in
water (they’re ionic)
- are electrolytes when in aqueous solutions
[Do Lab Exercise 5.A on page 195]
5.1 Chemical Analysis pg. 194 or pg. 227
*must be done for the start of lab
Problem: copy from text
Prediction:
Substance
Solubility in
Water
Litmus
Conductivity
Design: Summarize lab in 2 –3 sentences.
M.V. & R.V
Procedure: very detailed, anyone should be able to
follow
Evidence: setup a table to record data
Substance
Solubility
Litmus
Water
1
2
3
4
Conductivity
Analysis:
Identify 4 unknowns (include a brief explanation for
each)
Evaluation :
- comment of lab (is procedure adequate at finding
unknown solids?)
H.W.
1) Lab Exercise 5-A pg. 195
2) pg. 195 #2, 4,5,6
3) prelab