How is the Strength of an Acid Determined?
Bayside High School, Bayside, Queens
Summer Research Program for Science Teachers
Aim: How is the strength of an Acid defined?
Electric Pickle set up: 2 stands, 2 claps, to corks with iron nails ( 3-4”) in each Cork, and wire with plug at one end. Dill Pickles
Conductance set up: light blub with electrodes and wire plug. 6 beakers, HCl(aq), CH3COOH(aq), NaCl, Sugar, ethanol, NaOH, lemon, lime, O.J.
Electrolytes handout (class set)
1) Describe how conductance can be measured?
2) Distinguish among the properties of non electrolyte, strong electrolyte, and weak
3) Define: ionization
4) Identify & compare the dissociation of ionic and molecular compounds in
5) Describe what determines a strong acid/base and a weak acid/base
Do Now: (1) complete and balance the following equation
HNO3(aq) + KOH (aq) ---------à ___________ + ___________
(2) using Reference Tables, give the names of all the compounds above
Each and everyone WATCH Demo: Electric Pickle
1. Q Why does it light up? Complete circuit (flow of electrons)
2. Q What do we need to conduct electricity? (flow of e’s, moving charges, an electrolyte)
3. Q What is in the pickle which aids the flow of e’s? (water, salt, vinegar)
4. Q How are pickles made? Recipe for pickles? Label? (water,salt,vinegar,dill,garlic)
5. Q Does NaCl (s) have charges? What charges do they have? YES, Na+, Cl-
6. Q Will it conduct electricity? No why? (charges can not move in solids)
7. Q Will NaCl (aq) conduct electricity? Yes Why? (b/c charges can flow)
Remember: What did you learn about vinegar?
8. Q Does vinegar have charges? Yes, why? Acid = Electrolyte
CH3COOH(aq) --------à CH3COO-(aq) + H+(aq)
When solutions contain charged particles, they can carry e’s (electricity) so the light bulb lights up.
9. Q What do you think the word CONDUCTANCE means?
Conductance- a measure of a solution’s ability to conduct.
Electrolytes- any substance when dissolved in solution will break up(dissociate/ionize) and conduct an electric current.
Ex: NaCl(aq) ----------à Na+(aq) + Cl-(aq)
Dissociates- ionic compounds break apart giving ions(charged particles)
10.Q What do you think the word non electrolyte means?
Nonelectrolyte – any substance when dissolved in solution will NOT conduct electricity
Usually covalent compounds, with exception of acids
Ex: Sugar(s) C6H12O6(aq) -------à
Handout Electrolytes Worksheet
Ask a volunteer read the directions out loud.
Q Does anyone have questions?
Student will do:
Q7 C2H5OH ethanol
Ask volunteers to give answers from the handout.
Q. OJ, lemonade, soda are acids, yet we drink them. Why won’t we drink HCl(aq), it is in our
Q. Why do we wear gloves when handling HCl(aq)? And not OJ?
Write the following on the board:
Observation light intensity
HCl(aq) -----à H+ (aq) + Cl-(aq) (bright) (strong Acid - st electrolyte)
CH3COOH (aq) ------à H+(aq) + CH3COO- (dim) (weak Acid - weak electrolyte)
11. Q Which is the stronger Acid? Why? (Brighter)
S pair/share(1 min)
12. Q How is the strength of an acid defined using the data I just gave you?
13 Q What does the strength of an acid /base depend on?
Strength of an acid/base depends on the degree of ionization/dissociation in water
Strong acid (st electrolyte) most of the substance breaks apart( ionizes/dissociates) into ions
Many ions in solution, ionizes completely
Weak acid (wk electrolyte) very few molecules break apart to form ions in solutions
Most of the molecules remain intact.
Have very few ions in soln.
Using short but complete sentences and using four of the new vocabulary words you learnt in class answer the following question. (hand in at end of class as they leave).
Q Why is it safe to drink Orange Juice and not Hydrochloric acid?
If time available : Share out one or two student summaries.
Homework: finish Electrolytes Handout,
R P 605-611 P.611Q24,28,29
Prentice Hall, Chemistry textbook.Wibraham, Staley, Matta, Waterman
NYSPS (New York State Performance Standards)
S1c – Demonstrates an understanding of chemical reactions
S5b – Use concepts from Science Standards 1 to 4 to explain a variety of observations and phenomena
S5f - works individually and in teams to collect and share information and ideas
S6b – Records and stores data using a variety of formats
S7c – Explains a scientific concept or procedure to other students