SCH 4C - Acids & Bases

Acids & Bases – Arrhenius Definition

Acids – substances that release H⁺ ions into solution when dissolved in water (HX) 

• common acids are HCl(aq), HNO₃(aq), H₂SO₄(aq), H₃PO₄(aq), HC₂H₃O₂(aq), H₂CO₃(aq)

• when an acid molecule is placed in water, it reacts with a water molecule 

 

Ionization – a reaction in which electrically neutral molecules or atoms produce ions:

HCl(aq)  +  H₂O(l)  →  H₃O⁺(aq)  +  Cl^-(aq)     ionization equation

As seen above, the hydronium ion, H₃O⁺, forms from the combination of H₂O and H⁺ and it is responsible for the acidic properties

Since the hydronium ion is simply a hydrated H⁺ ion, the above equation can be simplified:

HCl(aq)  →  H⁺(aq)  +  Cl^-(aq)     simplified ionization equation

 

Bases – substances that release OH^- ions into solution when dissolved in water (MOH)

• common bases are group I & II metal hydroxides, like NaOH & Ca(OH)₂

 

Indicator – a dye that shows a different colour in acidic solution than it does in basic solution (ex. phenolphthalein, bromthymol blue).

Check out the cool way this high school student has used the colour changing properties of indicators to make a difference in the world.  Wow! 

 

Weak & Strong Electrolytes

Electrolytes – substances that release ions into solution when dissolved in water (acids - H⁺; bases - OH^-)

Dissociation – the separation of a substance into its ions when dissolved in water

NaCl(s)→  Na⁺(aq)  +  Cl^-(aq)

• electrolyte solutions will conduct electricity due to the dissociated ions in solution

 

Strong electrolytes (strong acid/ base) – electrolytes that completely ionizes in solution

HCl(aq)  →  H⁺(aq)  +  Cl^-(aq)     100% dissociation

• common strong acids: HCl(aq), HNO₃(aq), H₂SO₄(aq) 
• common strong bases: group I & II metal hydroxides

 

Weak electrolytes (weak acid/base) – electrolytes that partially ionizes in solution

HC₂H₃O₂(aq)  ↔  H⁺(aq)  +  C₂H₃O₂^-(aq)     1.3% dissociation

• common weak acids: HC₂H₃O₂(aq), H₂CO₃(aq) 
• common weak bases: non-group I & II metal hydroxides

  

Concentration vs Strength

Concentrated electrolyte solution – contains a large amount of solute in the solution (can of frozen orange juice)

Dilute electrolyte solution – contains a small amount of solute in the solution, (mixed up pitcher of orange juice)

• both strong or weak electrolytes can be concentrated or dilute (a 0.050 mol/L hydrochloric acid solution is a dilute strong acid solution)

 

Solutions from a Stock Acid

Recall that acid solutions are made from a concentrated stock solution, using 

c_cV_c = c_dV_{d     OR}      c_cV_c = c_dV_d

• remember the safety precautions (goggles, fume hood)

 

Homework:

Practice, p. 300 # 1-3

Section Questions, p. 304 # 3, 6, 7

 

Fill in the following chart (use the internet to find the info).  Normally we would do a lab to get this info, but whatcha gonna do?  

For the "conductivity" section, find out if acid and/or base solutions are conductive.  For the "indicator" sections, find out the colour the indicator would display in an acid or a base.  For the "reaction" sections, find out if a reaction occurs or not.

Answers: