Embedded Files
Lesson Instructions
Lesson Instructions
Review the learning goals and success criteria for Lesson 11: Acid-Base Properties of Salt Solutions.
Review the minds on, action, and consolidation sections of the lesson, completing any tasks as outlined.
Complete the fill-in-the-blanks handouts that have been provided to you.
Practice and apply what you've learned by completing the practice tasks outlined at the end of the lesson.
Learning Goals
Learning Goals
I am learning to …
Describe the properties of a salt based on the type of reaction it is formed by
Determine the pH of a solution containing a salt
Success Criteria
Success Criteria
I am able to …
Predict whether a salt will be basic, acidic, or neutral
Calculate the pH of a solution containing a salt
Sort various salts based on whether they form acidic, basic, or neutral solutions when dissolved in water.
Minds-On
Minds-On
Did you know that determining the acid-base properties of salt solutions are important for .... maintaining the pH of a swimming pool? Yup!
Read below to find out how the pH of a swimming pool can be increased or decreased using acids and bases, such as hydrochloric acid, sodium bisulfate, and sodium carbonate.
We all enjoy a cool dip in a swimming pool on a hot day, but we may not realize the work needed to keep that water safe and healthy. The ideal pH for a swimming pool is around 7.2. The pH will change as a result of many factors. Adjustment can be accomplished with different chemicals depending on the tested pH. High pH can be lowered with liquid HCl (unsafe material) or sodium bisulfate. The bisulfate anion is a weak acid and can dissociate partially in solution. To increase pH, use sodium carbonate. The carbonate anion forms an equilibrium with protons that results in some formation of carbon dioxide
Source: https://courses.lumenlearning.com/cheminter/chapter/calculating-ph-of-salt-solutions/
Action
Action
What is a Salt?
What is a Salt?
A salt is an ionic compound containing a cation and an anion
A salt is produced in neutralization reactions.
Recall, a neutralization reaction occurs between an acid and a base, producing a salt and water.
The cation of the salt comes from the base and the anion comes from the acid.
What’s a cation and an anion? Ions form from atoms that gain or lose valence electrons, resulting in a net positive or negative charge. Those with a negative charge are called anions (gain electrons), and those with a positive charge are called cations (lose electrons).
Figure 1. Reaction model used when determining the origins of cations and anions.
Salts produced from neutralization reactions can be acidic, basic, or neutral.
The pH of the salt formed is dependent upon whether the ions are conjugates of strong or weak acids and bases.
Reminder: What are the strong acids & bases, and weak acids & bases?
Reminder: What are the strong acids & bases, and weak acids & bases?
The table below summarizes the strong/weak acids and bases.
*Remember: you need to be able to identify strong acids and bases using the criteria below.
Figure 2. Table summarizing the strong and weak acids and bases.
Recall, a strong acid or base will have a conjugate with negligible acid/base properties (it will not react with water).
Figure 3. In the first reaction, HCl is a strong acid, which means it has a conjugate base, Cl-. Since HCl is a strong acid, hydronium is a product. In the second reaction, NaOH is a strong base, which means Na+ is its conjugate acid. Since NaOH is a strong base, hydroxide is a product. Note, strong acids and strong bases are unidirectional reactions, meaning, they only occur in the forward reaction. The reverse reaction can not and will not occur.
A weak acid or base will produce a conjugate that has weak acid/base properties (it will react with water).
Figure 4. Reactions involving weak acids and bases are multi-directional, meaning they can occur in the forward or reverse direction. Weak acids have weak conjugate bases, and weak bases, have weak conjugate acids. Thus, the reactions can occur in either direction as seen in the examples above with the weak acid, acetic acid, and weak base, ammonia.
Salts that Produce Neutral Solutions: e.g., NaCl, Ca(NO3)2, KBr
Salts that Produce Neutral Solutions: e.g., NaCl, Ca(NO3)2, KBr
Cation (e.g., Na+) is the conjugate of a strong base (NaOH) and therefore has negligible acidic properties
Anion (e.g., Cl-) is the conjugate of a strong acid (HCl) and therefore has negligible basic properties.
Neither of the ions acts as an acid or a base, and thus the pH is neutral
A salt produced in the reaction of a STRONG ACID and STRONG BASE will be NEUTRAL
Salts that Produce Acidic Solutions: e.g., NH4Cl
Salts that Produce Acidic Solutions: e.g., NH4Cl
Cation (NH4+) is the weak conjugate acid of a weak base (NH3). This conjugate acid would thus react with water to produce H3O+
NH4+ + H2O <-> NH3 + H3O+
Anion (Cl-) is the conjugate of a strong acid (HCl) and therefore would have negligible basic properties.
Cation acts as an acid; anion has no effect on pH
A salt produced in the reaction of a STRONG ACID and WEAK BASE will be ACIDIC
Example 1. What is the pH of a 0.35 mol/L NH4Cl solution? (Kb for ammonia is 1.8 x 10-5)
Example 1. What is the pH of a 0.35 mol/L NH4Cl solution? (Kb for ammonia is 1.8 x 10-5)
Watch the following video solution to example 1. Please copy this solution into your notes.
Salts that Produce Basic Solutions: e.g., NaCH3COO
Salts that Produce Basic Solutions: e.g., NaCH3COO
Anion (CH3COO-) is the weak conjugate base of a weak acid (CH3COOH). This conjugate base would thus react with water to produce OH-.
CH3COO- + H2O <-> CH3COOH + OH-
Cation (Na+) is the conjugate of a strong base (NaOH), and therefore will have negligible acidic properties.
Anion acts as a base; cation has no effect on pH.
A salt produced in the reaction of a WEAK ACID and STRONG BASE will be BASIC.
Example 2. Calculate the pH of a solution that contains 12.5 g of sodium acetate (NaCH3COO) dissolved in 1.0 L of H2O. (Ka for acetic acid is 1.8 x 10-5)
Example 2. Calculate the pH of a solution that contains 12.5 g of sodium acetate (NaCH3COO) dissolved in 1.0 L of H2O. (Ka for acetic acid is 1.8 x 10-5)
Watch the following video solution to example 2. Please copy this solution into your notes.
What if the salt contains an ion that is amphoteric?
What if the salt contains an ion that is amphoteric?
Remember, amphoteric means the ion can act as an acid or a base.
In order to determine of the salt contains an ion that is amphoteric, follow the example below.
Example 3. Determine if the solution of KH2PO4 acidic or basic?
Example 3. Determine if the solution of KH2PO4 acidic or basic?
Watch the following video solution to example 3. Please copy this solution into your notes.
Salt Solutions
Salt Solutions
Now that you can determine how salts are formed, you can sort salts based on whether they form acidic, neutral, or basic solutions when dissolved in water.
Recall some key summaries that were identified above:
A salt produced in the reaction of a STRONG ACID and STRONG BASE will be NEUTRAL.
A salt produced in the reaction of a STRONG ACID and WEAK BASE will be ACIDIC.
A salt produced in the reaction of a WEAK ACID and STRONG BASE will be BASIC.
Example 4. Sort the following salts based on whether they form acidic, neutral, or basic solutions when dissolved in water: NaCl, C5H5NHCl, NH4NO3, LiF, NaClO, KCN.
Example 4. Sort the following salts based on whether they form acidic, neutral, or basic solutions when dissolved in water: NaCl, C5H5NHCl, NH4NO3, LiF, NaClO, KCN.
Watch the following video solution to example 4. Please copy this solution into your notes.
This lesson is now complete. Consolidate your learning by completing the self-check below and the assigned practice questions.
Self-Check
Self-Check
How prepared am I to start my homework? Can I ...
Predict whether a salt will be basic, acidic, or neutral
Calculate the pH of a solution containing a salt
Sort various salts based on whether they form acidic, basic, or neutral solutions when dissolved in water.
Practice
Practice
Using your textbook, complete the following questions:
p534 #1
p536 #1,2
p539 #1
Complete the worksheet, Acidity of Salts.
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