Name: ____/____/_________ WS04 – Electrical Conductivity, Acids, Bases, Salts I. GRADE 10 Electrical Conductivity Ability to allow an electric current to flow through it. • Electrolyte: substance in which an electric current flow through the solution. • Nonelectrolytes: substances soluble in water, but do not conduct electricity. • Electrolyte solution: substance that contain an electrolyte Example 1 – Classify the substances below in electrolytes or nonelectrolytes: NaCl dissolved in water C12H22O11 dissolved in water HCl dissolved in water Example 2 – Complete: When an electrolyte is dissolved, __________ are formed, conducing electricity. When an nonelectrolyte is dissolved, ____________ are formed, _____ conducing electricity. II. Electrolytic Dissociation Separation of a dissolved compound into two ions of opposite charges. Example 2 – Complete the chemical equation of the electrolytic dissociation below: a. Dissociation of NaCl: b. Dissociation of C12H22O11: c. Dissociation of HCl: 1 Name: ____/____/_________ WS04 – Electrical Conductivity, Acids, Bases, Salts III. GRADE 10 The Strength of Electrolytes Degree to which it dissociates into ions. The higher the degree of dissociation, the stronger the electrolyte. • Strong electrolyte: Practically all the molecules of the solute dissociate in water, forming ions. • Weak electrolyte: Only some of the molecules dissociate, forming ions. The others remains neutral (neither positively or negatively charged) • Nonelectrolyte: None of the molecules dissociate, forming ions. Example 3 – Observe the degree of dissociation of the substances below and classify in strong, weak or nonelectrolyte: a) Initial Condition → NaCl(s) Na+(aq) + 100 molecules After dissolution b) 100 ions HF(aq) → Initial Condition 100 molecules After dissolution 92 molecules c) C12H22O11(s) Initial Condition 100 molecules After dissolution Cl-(aq) 100 ions H+(aq) + 8 ions → F-(aq) 8 ions C12H22O11(aq) 100 molecules 2 Name: ____/____/_________ WS04 – Electrical Conductivity, Acids, Bases, Salts IV. GRADE 10 Types of Electrolytes Acids, bases and salts are three important types of electrolytes with different properties. • Acids: i. Sour taste ii. Releases H+ (cation) ions in an aqueous solution iii. Chemical formula often begins with the symbol of a hydrogen atom (H). Exception – Acetic acid (vinegar) – CH3COOH iv. Name: substance + ic + acid v. Litmus paper – turns red • Bases: i. Bitter taste ii. Releases OH- (anion) ions in an aqueous solution iii. Chemical formula often begins with a metal and usually ends with the group OH. Exception – ammonium hydroxide (NH4OH) iv. Name: substance + hydroxide v. Litmus paper – turns blue • Salts: i. Salty taste ii. Releases a cation and an anion other than H+ and OHiii. Chemical formula formed by a metal and one or more non-metals iv. Name: metal + nonmetal + ide (or ate, ite) v. Litmus paper – no reaction (no change color) 3 Name: ____/____/_________ WS04 – Electrical Conductivity, Acids, Bases, Salts GRADE 10 Example 4 – Write the chemical formula, the dissociation and classify in acids, bases or salts: Substance Chemical formula Dissociation Classification Hydrochloric acid Sodium hydroxide Sodium chloride Sulphuric acid Silver nitrate Magnesium hydroxide Calcium chloride Acetic acid Ammonium hydroxide V. pH (potential Hydrogen) The pH scale (ranges from 0 to 14) is a scale used to rank the relative basicity or acidity of substances based on the amount of hydrogen ion (H+) activity in a substance. • pH < 7: acidic • pH = 7: neutral • pH > 7: basic The pH scale is logarithmic, which means that a difference of one unit between two substances indicates that one of the substances is 10 times more acidic or more basic than the other. 4 Name: ____/____/_________ WS04 – Electrical Conductivity, Acids, Bases, Salts GRADE 10 Example 5 – Complete the table with the pH of common substances and classify in acidic, basic or neutral. Substance pH Classification Bleach Gastric Acid Soda Pure water Ammonia Saliva Battery acid Drain cleaner Urine Example 6 – Observing the table above, calculate how many times one substance is more acidic (or basic) than the other substance. a) Bleach and drain cleaner b) Gastric acid and soda c) Acid rain and pure water 5 Name: ____/____/_________ WS04 – Electrical Conductivity, Acids, Bases, Salts GRADE 10 PRACTICE 1. Name and classify the substances in acids, bases, or salts and write the balance chemical equation to represent the dissociation: Name Chemical formula Dissociation Classification KCl HF HCl KOH FeBr3 NaNO3 HNO3 NaCl CaCl2 NH4Cl NaOH Na2SO4 Mg(OH)2 H3PO4 CuCl2 H2SO4 Ca(OH)2 H2CO3 NH4OH Al(NO2)3 HNO2 H2 S HBr 6 Name: ____/____/_________ WS04 – Electrical Conductivity, Acids, Bases, Salts GRADE 10 2. Write balanced chemical equations to represent the dissociation of the compounds below and classify them in acid, base or salt: a. Sodium acetate b. Ammonium sulfate c. Calcium carbonate d. Potassium carbonate e. Sodium hydroxide f. Iron (II) sulfate g. Lead (II) phosphate h. Iron (III) chloride i. Copper (II) sulfate j. Mercury (II) sulfide k. Zinc chloride l. Lead (II) acetate 7 Name: ____/____/_________ WS04 – Electrical Conductivity, Acids, Bases, Salts GRADE 10 3. A student mixes strawberry and water. A pH meter shows a pH of 5.4. a. Is strawberry acidic, basic, or neutral? b. In this mixture, must there be more of hydrogen ions or hydroxide ions? Why? 4. A student adds alka-seltzer tablet to the strawberry mixture and stirs. The pH meter now reads 8.3. What was released by the alka-seltzer tablet to cause this change? 5. Bromothymol blue is a chemical indicator that is blue in basic and neutral solutions, an turns greenish and then yellow as the solution becomes more and more acidic. Fill the table below with the color would bromothymol blue would be and answer the following questions: Situation pH Water directly out of tap pH = 7.2 Bromothymol blue color pH after exhaled air is blown through a straw into pH = 5.1 water for 5 min pH with 2mL of bleach added to the water pH = 9.4 pH with instant coffee added to the water pH = 5.0 pH after an aquatic plant is grown in water for pH = 7.7 three days in bright sunlight pH after a snail has lived in water for three days pH = 5.8 a. What effect does carbon dioxide have on tap water? b. Is bleach an acid or a base? c. Is coffee an acid or a base? 8