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

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


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


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!


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


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


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


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


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


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


Bases

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)



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


Acid or base? Alien juice bar game


http://sv.berkeley.edu/showcase/flash/juicebar.html

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

Documents

hydrogen atom

hydroxide ions oh

antacidsstrong bases

bases arehow

protons hydrogen ionbases

sodium ions na

hydrogen chloride hcl

waterbased solution