Exam 2 Pt. 4 - Titrations and Solubility

What is usually the goal of a titration?

• Known M of base (NaOH) to determine molarity of unknown acid

What does a buret contain?

• Contains base

What does the Erlenmeyer flask contain?

• Contains acid

How do you determine initial pH of a strong acid solution?

• [HA]=[H3O+]

plug into pH = -log[H3O+]

How do you determine initial pH of a strong base solution?

• [A-]=[OH-]

plug into pOH = -log[OH-]

pH = 14 - pOH

What are you always adding in a titration reaction?

• Always only adding base (NaOH)

In titrations, what is always being added to the acid? What reaction results from this?

• Adding base (NaOH)

Neutralization reaction; BCA table

What is a neutral salt? Do we include this in the pH?

• When both cation and anion are neutral

ignore for pH calculation

After forming BCA table, and only strong acid and neutral salt is left, how do you find pH?

• Solve for pH of a strong acid ([HA]=[H3O+])

ignore neutral salt

After forming BCA table, and only neutral salt is left, how do you find pH?

• Assume pH = 7

nothing affecting pH

After forming BCA table, and only strong base and neutral salt is left, how do you find pH?

• Solve for pH of strong base ([A-]=[OH-])

ignore neutral salt

What are the steps to solving for the pH when only strong acid is left over?

1. Find [HA] after neutralization reaction (BCA)

2. Find [H3O+]; [HA]=[H3O+]

3. Find pH

What must you do before finding [H3O+] from mols of HA from BCA table?

• Convert mols to M

Volumes added

What are the steps to solving for the pH when only strong base is left over?

1. Find [A-] after neutralization (BCA table)

2. Find [OH-]; [A-]=[OH-]

3. Find pH; pOH —> pH

What are the steps to finding initial pH of a weak acid?

1. Hydrolysis of acid

2. Plug into ICE table

3. Set expression equal to Ka to solve for x

4. Solve for pH

After forming BCA table when weak acid and basic salt (CB) are left, how do you find pH?

• Solve for pH of buffer

How do you solve for pH of buffer?

• WA and CB; plug in HH equation

After forming BCA table when only basic salt (CB) is left, how do you find pH?

• Solve for pH of basic salt (weak base)

Before going from BCA table to ICE table what must be done?

• Converted to M; volumes are additive

mL—> L

How do you solve for pH of basic salt?

1. Hydrolysis of basic anion

2. Plug into ICE table

3. Set expression equal to Kb to solve for x

4. Solve for pH

Is a basic salt a weak base?

• Yes always weak 

After forming BCA table when strong base and weak base (basic salt) are left, how do you find pH?

• Solve for pH of strong base; ignore weak base

mixture of bases rule

How do you solve for pH of strong base?

• [A-]=[OH-]; plug into pH = -log[OH-]

pOH = 14 - pH

What is the solubility product constant?

• Ksp = [products]^(coefficients)

What is molar solubility (s)?

• The maximum molarity than can be dissolved

What are the steps to solving for s when given Ksp and decomposition reaction of solid?

1. Plug in reaction to ICE table

2. Assume all molarities are 0 and add S (with coefficients)

3. Solve for s by setting expression equal to Ksp

In what step of the ICE table do you include coefficients (ratio)?

• In “C” area; include coefficients

still square in expression

When comparing solubility of two compounds, do you look at the Ksp or s?

• Look at the S; when ratios are not  the same

When a compound is dissolved in a solution with a common ion, what occurs to its solubility?

• Solubility is lowered; than in pure water

What solution are basic compounds more soluble in?

• Acidic solutions

What solution are acidic compounds more soluble in?

• Basic solutions

What solution are neutral compounds more soluble in?

• pH doesn’t affect neutral compounds

When predicting whether two ions will form a precipitate, what do you use?

• Q = [products]^(coefficients)

Will a precipitate form when Q<Ksp?

• No precipitate

Will a precipitate form when Q=Ksp?

• No precipitate

Will a precipitate form when Q>Ksp?

• Precipitate will form; excess ions

When concentrations of two compounds before mixing, what equation do you use to find final concentration of each ion?

• M1V1=M2V2

solve for M2; OF EACH ION

Once final concentrations of each ion are obtained, what do you plug it into?

• Plug into Q expression; to solve for Q

Once Q is obtained, what do you compare it to to determine if precipitate will form?

• Compare Q to Ksp value given