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8.1: A solution is a type of mixture 8.2: The amount of solute that dissolves can vary

Unit: Chemical Interactions Chapter 8 : Solutions When substances dissolve to form solutions, the properties of the mixture change. 8.1: A solution is a type of mixture 8.2: The amount of solute that dissolves can vary 8.3: Solutions can be acidic, basic, or neutral

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8.1: A solution is a type of mixture 8.2: The amount of solute that dissolves can vary

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  1. Unit: Chemical InteractionsChapter 8: SolutionsWhen substances dissolve to form solutions, the properties of the mixture change. 8.1: A solution is a type of mixture 8.2: The amount of solute that dissolves can vary 8.3: Solutions can be acidic, basic, or neutral 8.4: Metal alloys are solid mixtures

  2. 8.3: Solutions can be acidic, basic, or neutral 8.3 Solutions can be acidic, basic, or neutral • Before, you learned: • Substances dissolved in solutions can break apart into ions • Concentration is the amount of a substance dissolved in a solution • Water is a common solvent • Now, you will learn: • What acids and bases are • How to determine if a solution is acidic or basic • How acids and bases react with each other

  3. 8.3: Solutions can be acidic, basic, or neutral Review • Draw and label two solutions • One is more dilute and the other is more concentrated

  4. 8.3: Solutions can be acidic, basic, or neutral Acids and bases have distinct properties • Acids • Tend to taste slightly sour when dissolved in water • Produce a burning or itchy feeling on the skin • Found in many foods: OJ, tomatoes, vinegar • Never touch or taste a strong acid • Bases (chemically opposite) • Tend to taste bitter • Often feel slippery to the touch • Found in many household products: soap, ammonia, antacids • Strong bases are also dangerous chemicals

  5. 8.3: Solutions can be acidic, basic, or neutral Acids, Bases, and Ions (1) • Generally, a compound that is an acid or base acts as such only when it is dissolved in water! • In the water-based solution, the compounds produce ions • Ex: if a hydrogen atom (one proton and one electron) loses an electron, it becomes a hydrogen ion = a proton • Acid: a substance that can donate a hydrogen ion (a proton) to another substance • Ex: hydrogen chloride (HCl) dissolved in water, the hydrogen and chloride ions separate • Hydrogen is free to react with other substances • HCl dissolved in water = hydrochloric acid! H2O HCl H+ + Cl-

  6. 8.3: Solutions can be acidic, basic, or neutral Acids, Bases, and Ions (2) • Base: a substance that can accept a hydrogen ion from another substance • Ex: sodium hydroxide (NaOH) dissolved in water, it separates into sodium ions (Na+) and hydroxide ions (OH-) • The hydroxide ions are then free to accept protons from other substances • Solution that results when NaOH is dissolved in water is called sodium hydroxide

  7. 8.3: Solutions can be acidic, basic, or neutral Acids, Bases, and Ions (3) • Atomic level difference: • Acids donate protons (hydrogen ion) • Bases accept protons • When a proton from an acid is accepted by a hydroxide ion from a base, a molecule of ________ is formed

  8. 8.3: Solutions can be acidic, basic, or neutral Characteristics of Acids • Safe ways to test for an acid • Place a few drops of a solution on a compound that contains a carbonate (CO3), and a reaction occurs producing CO2 (gas) • ex: limestone (CaCO3) • Acetic acid (abbreviated “HA” here) touching a piece of limestone: • 2 HA + CaCO3 ---> H2O (l) + CO2 (g) + CaA2(aq) • Acids also react with most metals • The reaction produces hydrogen gas • 2HCl + Zn  H2 + ZnCl2 • Ability to change the colors of certain compounds known as acid-base indicators • Ex: litmus • Acids will turn litmus paper red

  9. 8.3: Solutions can be acidic, basic, or neutral Characteristics of Bases • Feel soapy or slippery because they react with acidic molecules in your skin: fatty acids • Fatty acids in your skin + a base (usually sodium hydroxide)  soap! • Also change colors of acid-base indicators • Bases turn litmus paper blue • Will counter the effects of an acid • Few drops of acid, then a few drops of base, the litmus papers will change in response to each

  10. 8.3: Solutions can be acidic, basic, or neutral The strength of acids and bases can be measured (1) Acids • Juices we drink contain acids • Car battery fluid contains acids, but you don’t drink that! • Wash hands with soap, which contains a base • Don’t touch the liquid used to unclog drains! • …some acids and bases are stronger than others • Strong acids break apart completely into ions • Ex: When hydrogen chloride (HCl) dissolves in water  hydrochloric acid, it first breaks down completely into hydrogen and chloride ions • Weak acids do not form many ions in solution • Ex: acetic acid (HC2H3O2) dissolves in water, only about 1% of the acetic acid breaks up into ions • The other 99% remains unchanged • Weak acid

  11. 8.3: Solutions can be acidic, basic, or neutral The strength of acids and bases can be measured (2) Bases • When sodium hydroxide (NaOH) dissolves in water  it breaks completely down to sodium ions (Na+) and hydroxide ions (OH-) • Strong base • When ammonia (NH3) dissolves in water, only about 1% of the ammonia reacts with water to form OH- ions • NH3- + H2O  NH4+ + OH- • The other 99% of the ammonia remains unchanged • Weak base

  12. 8.3: Solutions can be acidic, basic, or neutral

  13. 8.3: Solutions can be acidic, basic, or neutral Measuring Acidity • Acidity of a solution depends on the concentration of H+ ions in the solution • Measured on the pH scale • A high H+ concentration is indicated by a low number • A low H+ concentration is indicated by a high number • Range 0 to 14 (but can be beyond), middle is 7 (neutral solution, neither acid or base) • Pure water has a pH of 7 • pH of concentrated hydrochloric acid is < o • pH of concentrated sodium hydroxide (NaOH) > 0 • Modern instruments can measure pH with a probe • Older method: acid base indicators • Ex: litmus paper (acids turn it red, bases turn it blue)

  14. 8.3: Solutions can be acidic, basic, or neutral What are the strong acids on the chart? Where are the strong bases? How does the concentration of hydrogen ions change?

  15. 8.3: Solutions can be acidic, basic, or neutral Acids and bases neutralize each other • Acids donate hydrogen ions • Bases accept hydrogen ions • Acids and bases react when they come into contact • (recall: H+ + OH-  H2O) • Negative ion of an acid (Cl-) joins with a positive ion of a base (Na+) to form a salt • Salt and water are neutral • An acid-base reaction is called a neutralization reaction • The reactants are an acid and a base, the products are salt and water • Ex: antacid table: stomach pH is 1.5 (hydrochloric acid in the stomach lining) • Antacid contains a base (ex: sodium bicarbonate) • The base reacts with the stomach acid and produces a salt and water • Also: acid rain: gases in the atmosphere dissolve in water vapor  acidic solutions

  16. 8.3: Solutions can be acidic, basic, or neutral • Acid or base? Alien juice bar game

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