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 8.4: Metal alloys are solid mixtures

 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 8.3: Solutions can be acidic, basic, or neutral 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 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 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! 8.3: Solutions can be acidic, basic, or neutral HCl H2O H + + Cl -

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

The strength of acids and bases can be measured (1)  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 8.3: Solutions can be acidic, basic, or neutral Acids

The strength of acids and bases can be measured (2)  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 8.3: Solutions can be acidic, basic, or neutral Bases

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) 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?

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 8.3: Solutions can be acidic, basic, or neutral

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