Unit: Chemical InteractionsChapter 8: Solutions
When substances dissolve to form solutions, the properties of the mixture change.
8.1: A solution is a type of mixture8.2: The amount of solute that dissolves
can vary8.3: Solutions can be acidic, basic, or
neutral8.4: 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
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
8.3: Solutions can be acidic, basic, or neutral