Chemistry for Engineers: pH and Acidity

Prayer Before Class

• A prayer is offered for guidance and understanding during the class.
• It requests wisdom, a clear mind, and good memory.
• It asks for understanding, ease of learning, and effective communication.
• The prayer also requests successful completion of the work.
• It ends with a declaration of faith and reverence.

Post-laboratory Discussion: Acidity, Basicity, pH

• This is a discussion on the post-laboratory findings of acidity, basicity, and pH.
• The discussion is part of the Chemistry for Engineers course.
• The session will address acidity, basicity, and pH.

Learning Objective

• Students are expected to determine the pH of various solutions.
• This task will be completed at the end of the experiment

Topic Outline

• Discussion of pH
• Measurement of pH
  • pH of acids and bases
  • pH of common solutions
  • pH of water
• Effect of Dilution on pH of acids and bases
• Acid-Base reaction
• Action of acids on metal

pH: Basicity, Acidity

• pH is a scale of small numbers used to indicate the molar hydronium ion concentration in aqueous solutions.
• This scale ranges from 0 to 14.
• 7 is neutral.
• Below 7 is acidic.
• Above 7 is basic.

pH: Basicity, Acidity (Advanced)

• A higher concentration of hydronium ions leads to a lower pH.
• A change of 1 pH unit represents a tenfold change in hydronium ion concentration

Acid

• An acid is any substance that produces H3O+ (hydronium ions) in an aqueous solution

Base

• A base is any substance that produces OH- (hydroxide ions) in an aqueous solution

pH Values of Common Solutions

• A table shows the pH values of various common materials.
• Different materials have varying pH levels, ranging from highly acidic to highly basic.

Strengths of Acids and Bases

• Acids and bases can be classified as strong or weak.
• This classification depends on the extent to which proton transfer occurs in an aqueous solution.

Strong Acid

• Strong acids react almost completely with water to form H3O+ ions.
• They ionize completely in water.

Weak Acid

• Weak acids produce much smaller concentrations of H3O+ ions.
• They only partially ionize in water.

Strong Base

• Strong bases (that are metal hydroxides) ionize completely in water.
• They produce OH- ions in aqueous solution.

Weak Base

• A weak base produces a much smaller concentration of OH- ions.
• They only partially ionize in water

Strong Acids and Bases (Table)

• A table lists the formulas and names of common strong acids and bases.

Strong Acids

• Sulfuric acid (H2SO4) is used in manufacturing fertilizers, dyes, pigments, and rayon.
• Hydrochloric acid (HCl) is used for removing rust, cleaning metal equipment, in household cleaners, and food manufacturing.
• Nitric acid (HNO3) is for engraving, cleaning metals, and manufacturing fertilizers.

Weak Acids

• Acetic acid (CH3COOH) is present in vinegar and the manufacture of paints, adhesives, and plastics

Strong Bases

• Sodium hydroxide (NaOH) is used in manufacturing glass and soap.

Weak Bases

• Ammonia (NH3) is used in fertilizers and as a cleaning agent.
• Magnesium hydroxide (Mg(OH)2) is used as a laxative and treats wastewater in metal-processing plants.

Acidic, Basic, Neutral Solutions

• Acidic solutions have a higher concentration of H3O+ ions than OH- ions.
• Basic solutions have a higher concentration of OH- ions than H3O+ ions.
• Neutral solutions have equal concentrations of OH- and H3O+ ions.

Some Factors Affecting pH of a Solution

• Factors that Affect pH include the concentration of acids or bases
• Presence of buffers
• Concentration of carbon dioxide

Concentration of the Solution

• Higher concentrations of acids lead to lower pH values (more acidic).
• Higher concentrations of bases lead to higher pH values (more basic).

Dissolved Salts

• Salts of strong acids and weak bases form acidic solutions.
• Salts of strong bases and weak acids form basic solutions.

Presence of Buffers

• Buffers prevent significant changes in solution pH.
• Neutralizing added acids or bases.
• Maintaining a stable pH in the solution.

Carbon Dioxide Concentration

• Carbon dioxide dissolves in water to form carbonic acid.
• This lowers the pH of the solution.

Properties of Acids and Bases

• Properties of acids and bases are discussed.

Neutralization

• Neutralization is a chemical reaction between an acid and a hydroxide base.
• This reaction results in the formation of salt and water

Application of Neutralization Reactions

• Neutralization is used in wastewater treatment using compounds like sodium bicarbonate, magnesium hydroxide, calcium oxide, and calcium carbonate.
• Neutralization can also be used to control soil pH using calcium carbonate and calcium hydroxide.

Reaction with Metals

• Strong acids react with certain metals to produce hydrogen gas and a salt.

Experiment Results

• This section details the experimental results for acidity, basicity, and pH measurements.

pH of Acids and Bases

• Measured pH values for various acidic and basic solutions with litmus paper and pH meter measurements.

pH of Common Solutions

• Observed and measured pH values for common solutions using litmus paper and pH meter.

pH of Water

• Measured pH values for boiled distilled, unboiled distilled and tap water.

Effect of Dilution on pH of Acids and Bases

• Experiment shows the effect of dilution on the pH of acidic and basic solutions.

Acid-Base Reaction

• Neutralization reaction pH values measured using litmus paper and comparing with pH meter.

Action of Acids on Metals

• The reactions of different concentrations of acids with metal ribbons are discussed, including the rate of reactions.

What Effect Does Dilution Have on the pH of an Acid (or Base)?

• Questions about the effect of dilution on the pH of acids and bases.

Dilution

• The process of diluting a solution by adding solvent, thereby affecting the solute concentration.

Effects on an Acid

• Dilution increases the pH of an acid.
• This is because the concentration of H3O+ decreases as more solvent is added.

Effects on a Base

• Dilution decreases the pH of a base.
• This is because the concentration of OH- decreases as more solvent is added.

As the Molar Concentration of an Acid Decreases…

• The reaction rate of the acid with metals is expected to decrease.

Molar Concentration of An Acid Affecting Reaction Rate

• Collision theory explains the conditions necessary for chemical reactions.
• Lower acid concentrations reduce the frequency of effective collisions, thereby slowing the reaction rate.

Explain Why Unboiled Deionized Water Has a Measured pH Less Than 7?

• Unboiled deionized water absorbs carbon dioxide from the air, forming carbonic acid.
• Carbonic acid dissociates into ions, decreasing the pH to less than 7.

References

• Provides a list of references for further reading.