Hydrolysis, Buffer and Titration

Hydrolysis, Buffer, Titration

by Luis Bello

​Summary

​14.4 Hydrolysis of Salts

​14.6 Buffers

14.7 Acid-Base Titrations

Multiple Choice

What is the purpose of an "indicator"?

• changes color if a chemical reaction occurs

• changes color if a physical change occurs

• changes color in the presence of an acid or base

• changes color when a salt dissolves in water

Multiple Choice

The table shows the pH of several solutions. Which solution has the greatest concentration (amount) of H⁺ ions?

• vinegar

• milk

• water

• bleach

Multiple Choice

Which of these will react with zinc to produce hydrogen gas?

• H₂SO₄

• NaOH

• H₂O

• KCl

Multiple Choice

Acids or bases that are "strong" __.

• always dissociate in water

• always have a high pH

• always have a high concentration

Multiple Choice

You have a solution that is a base. You want to lower the pH so you should ___.

• add a salt

• add an acid

• add more base

• wait until it evaporates

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​Hydrolisis

​By the end of this section, you will be able to:

• Predict whether a salt solution will be acidic, basic, or neutral

• Calculate the concentrations of the various species in a salt solution

• Describe the acid ionization of hydrated metal ions

​
Hydrolysis is a chemical reaction in which adding water molecules breaks down a compound. In this process, water molecules are split into hydrogen cations (H⁺) and hydroxide anions (OH⁻), and these ions interact with the chemical bonds of the compound, causing them to break apart.

Hydrolysis reactions are commonly observed in various biological, chemical, and industrial processes. For instance, in digestion, complex food molecules are broken down into simpler substances by hydrolysis reactions with the help of enzymes.

​Hydrolysis

​Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water.

Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt's constituent ions.

​

For example, dissolving ammonium chloride in water results in its dissociation, as described by the equation

Multiple Choice

What two substances must combine to make a neutral salt

• Strong acid and strong base

• Strong acid and weak base

• Weak acid and strong base

• Weak acid and weak base

Multiple Choice

What two substances must combine to make a basic salt

• Strong acid and strong base

• Strong acid and weak base

• Weak acid and strong base

• Weak acid and weak base

Multiple Choice

Which type of salt the following salt are classiffied as ?

"K₂SO₄"

• neutral salt

• acidic salt

• basic salt

Multiple Choice

Which type of salt the following salt are classiffied as ?

"NH₄Br"

• neutral salt

• acidic salt

• basic salt

Multiple Choice

Which type of salt the following salt are classiffied as ?

"LiCH₃COO"

• neutral salt

• acidic salt

• basic salt

​Buffer

​By the end of this section, you will be able to:

• Describe the composition and function of acid–base buffers

• Calculate the pH of a buffer before and after the addition of added acid or base

​A buffer solution is a solution that resists changes in its pH level when an acidic or basic substance is added to it. It achieves this by containing a weak acid and its corresponding conjugate base, or a weak base and its corresponding conjugate acid.

This combination allows the solution to absorb or release hydrogen ions (H⁺) or hydroxide ions (OH⁻) in response to the addition of an acid or a base, helping to maintain a relatively stable pH.

Buffers are essential in many biological and chemical processes where maintaining a specific pH level is crucial for proper functioning. For instance, in biological systems like the human body, various bodily fluids (such as blood) rely on buffer systems to maintain their pH within a narrow range. This is vital for enzymes and other biochemical processes to function optimally.

​If 1 mL of stomach acid [approximated as 0.1 M HCl(aq)] were added to the bloodstream and no correcting mechanism were present, the pH of the blood would decrease from about 7.4 to about 4.7—a pH that is not conducive to continued living.

​

Fortunately, the body has a mechanism for minimizing such dramatic pH changes.

​

​​Buffer: ,a solution that resists dramatic changes in pH.

Buffers do so by being composed of certain pairs of solutes: either a weak acid plus a salt derived from that weak acid or a weak base plus a salt of that weak base.

For example, a buffer can be composed of dissolved HC₂H₃O₂ (a weak acid) and NaC₂H₃O₂ (the salt derived from that weak acid).

​

Another example of a buffer is a solution containing NH₃ (a weak base) and NH₄Cl (a salt derived from that weak base).

Open Ended

Which combinations of compounds can make a buffer solution?

1-HCHO₂ and NaCHO₂

2-HCl and NaCl

3-CH₃NH₂ and CH₃NH₃Cl

4-NH₃ and NaOH

Open Ended

Can a buffer be made by combining a strong acid with a strong base? Why or why not?

Open Ended

What is the pH of a solution of 0.81 M acid and 0.65 M of its conjugate base if the ionization constant is 4.92 x 10^-7?

a)   6.21b)   6.40c)   6.62d)   6.81e)   5.80

​

14.7 Acid-Base Titrations

​

By the end of this section, you will be able to:

​

Interpret titration curves for strong and weak acid-base systems

Compute sample pH at important stages of a titration

Explain the function of acid-base indicators

​Calculating pH for Titration Solutions: Strong Acid/Strong Base

​A titration is carried out for 25.00 mL of 0.100M HCl (strong acid) with 0.100M of a strong base NaOH . Calculate the pH at these volumes of added base solution:

​

(a) 0.00 mL

(b) 12.50 mL

(c) 25.00 mL

(d) 37.50 mL

​​Titration of a Weak Acid with a Strong Base

Consider the titration of 25.00 mL of 0.100M CH₃CO₂H with 0.100M NaOH. The reaction can be represented as:

CH3CO2H+OH⁻⟶CH3CO⁻+H2O

​

Calculate the pH of the titration solution after the addition of the following volumes of NaOH titrant:

(a) 0.00 mL

(b) 25.00 mL

(c) 12.50 mL

(d) 37.50 mL

Multiple Choice

What is the endpoint of a titration

• Where the amount of acid and base are balanced according to the equation
• Where there is no base
• At the end

Multiple Choice

I am titrating 1M HCl with 1M NaOH.  I have 25mL of HCl. How much NaOH will I need?

• 2.5mL
• 5mL
• 25mL
• 50mL

Multiple Choice

what is the reading on this burette?

• 4.40mL
• 3.50mL
• 3.60mL
• 4.50mL

Multiple Choice

I have 25mL of 1M HCl which neutralises 20mL of NaOH. What is the concentration of the NaOH?

• 0.8 M
• 1 M
• 1.25 M

Multiple Choice

Identify the products of the chemical equation
3 LiOH + H₃PO₄ →

• Li₃PO₄ + 3 H₂O
• LiPO₄ + 3 H₂O
• Li(PO₄)₃ + 3 H₂O
• BOY + La + N₂

Multiple Choice

What acid and what base would you choose to prepare the salt potassium chlorate?

• KOH and HClO₃
• KOH and HClO₂
• HK and OHClO₃
• HK and OHClO₂

Multiple Choice

A 50.0 mL sample of Ca(OH)₂ is neutralized by 300.0 mL of HCl solution with a pH of 1.3. Calculate the molarity of the Ca(OH)₂ solution.

• 1.0 M
• 0.50 M
• 0.15 M 
• 0.30 M