Post Laboratory Discussion 3 - Acidity, Base, pH PDF

PRAYER BEFORE CLASS Holy Spirit, Divine Creator, true source of light and fountain of wisdom! Pour forth your brilliance upon my dense intellect, dissipate the darkness which covers me, that of sin and of ignorance. Grant me a penetrating mind to understand, a retentive memory, method and ease of le...

PRAYER BEFORE CLASS Holy Spirit, Divine Creator, true source of light and fountain of wisdom! Pour forth your brilliance upon my dense intellect, dissipate the darkness which covers me, that of sin and of ignorance. Grant me a penetrating mind to understand, a retentive memory, method and ease of learning, the lucidity to comprehend, and abundant grace in expressing myself. Guide the beginning of my work, direct its progress and bring it to successful completion. This I ask through Jesus Christ, true God, and true man, living and reigning with You and the Father, forever and ever. Amen.  UST General Santos Post-laboratory Discussion: Acidity, Basicity, pH CHEMISTRY FOR ENGINEERS Learning Objective at the end of the experiment, students are expected to: ❖ To determine the pH of various solutions Topic Outline ❖ Discussion ❖ 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 Scale - Scale of small numbers that is used to specify molar hydronium ion concentration in aqueous solution - The scale goes from 0 to 14 - 7 is neutral - Below 7 is acidic - Above 7 is basic pH: Basicity, Acidity 1. The higher the concentration of hydronium ion, the lower the pH value 1. A change in 1 unit in pH always corresponds to a tenfold change in hydronium ion concentration Acid - a substance that produces H3O+ ions in aqueous solution Base - a substance that produces OH- ions in aqueous solution pH values of common solutions Strengths of Acids and Bases - can be classified as strong or weak based on the extent to which proton transfer occurs in aqueous solution Strong Acid - reacts completely or almost completely with water to form H3O+ ions - an acid that ionizes completely in aqueous solution Weak Acid - produce much smaller concentration of H3O+ ions - acid that is only partially ionized in aqueous solution Strong Base - metal hydroxides - a base that ionizes completely in aqueous solution producing OH- ions Weak Base - produce much smaller concentration of OH- ions - acid that is only partially ionized in aqueous solution Strong Acids Sulfuric acid (H2SO4) - manufacturing fertilizer, dyes, pigments, and rayon Hydrochloric acid (HCl) - remove rust, clean metal equipment, household cleaners, and food manufacturing Nitric acid (HNO3) - engraving, clean and purify metals, and manufacturing fertilizer Weak Acids Acetic acid (CH3COOH) - present in vinegar, and to manufacture paints, adhesives, and plastics Strong Bases Sodium hydroxide (NaOH) - manufacture of glass and soap Weak Bases Ammonia (NH3) - fertilizers, and cleaning agent Magnesium hydroxide (Mg (OH)2) - laxative, treat wastewater in metal-processing plants, and flame retardant in plastics Acidic Solution - aqueous solution in which the concentration of H3O+ ion is higher than that of OH- ion Basic Solution - aqueous solution in which the concentration of OH- ion is higher than that of H3O+ ion Neutral Solution - aqueous solution in which the concentration of OH- and H3O+ ions are equal Some Factors Affecting pH of a Solution Acidity, Basicity, pH 1. Concentration of the Solution Acids - higher concentration of acids leads to a lower pH (more acidic) Bases - higher concentration of bases leads to higher pH (more basic) 2. Dissolved Salts - salts of strong acids and weak bases form acidic solutions - salts of strong bases and weak acids form basic solutions 3. Presence of Buffers - buffers prevent major changes in solution pH by neutralizing added acids or bases - presence of buffer maintains a relative stable pH of the solution 4. Carbon Dioxide Concentration - carbon dioxide dissolves in water to form carbonic acid, lowering the pH Properties of Acids and Bases Acidity, Basicity, pH Neutralization - chemical reaction between an acid and a hydroxide base to form salt and water Application of Neutralization Reaction: Wastewater Treatment - commonly used: sodium bicarbonate, magnesium hydroxide, calcium oxide, calcium carbonate Controlling soil pH - commonly used: calcium carbonate, calcium hydroxide Reaction with Metals - strong acids react with certain metals (active metals) to produce hydrogen gas and a salt Experiment Results Acidity, Basicity, pH A.1 pH of acids and bases SOLUTION LITMUS PAPER OBSERVED pH pH METER 0.1M HCl Blue → Red Acidic 0.2 Red → Red 0.1M CH3COOH Blue → Red Acidic 1.7 Red → Red 0.1M NaOH Red → Blue Basic 12 Blue → Blue A.2 pH of common solutions SOLUTION OBSERVED pH pH METER Vinegar Acidic 2.8 Lemon Juice Acidic 2.2 Household Ammonia Basic 11 Detergent Solution Basic 8-11 A.3 pH of water SOLUTION OBSERVED pH pH METER Boiled Distilled Water Neutral 7 Unboiled Distilled Water Acidic 5-6 Tap Water Basic 7.5-8.5 B. Effect of Dilution on pH of acids and basic solutions SOLUTION LITMUS PAPER OBSERVED pH 0.1M HCl Blue → Red Acidic Red → Red 0.01M HCl Blue → Red Acidic Red → Red 0.001M HCl Blue → Red Acidic Red → Red 0.0001M HCl Blue → Red Acidic Red → Red C. Acid-Base Reaction SOLUTION LITMUS PAPER OBSERVED pH 0.1M HCl and 0.1M NaOH BLUE LITMUS → BLUE Neutral RED LITMUS → RED 0.1M CH3COOH and 0.1M BLUE LITMUS → BLUE Neutral NaOH RED LITMUS → RED D. Action of acids on metals SOLUTION Mg RIBBON 6M HCl Fast (Formation of Gas) 3M HCl Fast (Formation of Gas) 0.1M HCl Slow (Formation of Gas) What effect does dilution have on the pH of (a) an acid? (b) base? Dilution - process of adding more solvent to a solution affecting the concentration of the solute. Effects on an Acid - dilution increases the pH of an acid - as you add more water to an acidic solution, the concentration of H3O+ decreases - Fewer H3O+ ions means a less acidic solution → higher pH value Basic Solution - dilution decreases the pH of a base - as you add more water to a basic solution, the concentration of OH- decreases - Fewer OH- ions means a less basic solution →lower pH value  As the molar concentration of an acid decreases, the reaction rate with an active metal is expected to? Explain. Molar Concentration of An Acid Affecting Reaction Rate - Collision theory - is a set of statements that give the conditions necessary for a chemical reaction to occur 1. Molecular collisions 2. Activation energy 3. Collision Orientation - a lower concentration of acid reduces the number of acid molecules available for collisions thus decreasing the frequency of effective collisions → slowing down the reaction rate Explain why unboiled deionized water has a measured pH less than 7?  Explain why unboiled deionized water has a measured pH less than 7? - When deionized water is exposed to air, it readily absorbs carbon dioxide - The absorbed carbon dioxide reacts with water forming carbonic acid - carbonic acid is a weak acid that dissociates partially in water → ↑ hydronium ions → acidic References ❖ Bettelheim, F. A, W. H., Brown, M. K. Campbell, S. O. Farrell & O. Torres. (2018). Introduction to General, Organic and Biochemistry, 11th ed. Boston, MA, USA: Cengage Learning ❖ Stoker, S.H. (2016). General, Organic, and Biological Chemistry, 7th ed. Belmont, CA, USA: Cengage Learning