Acids and Bases

Nevada State Standards  P.5.A.3. Students know materials can be classified by their observable physical and chemical properties.  N.8.B.2 Students know scientific knowledge is revised through a process of incorporating new evidence gained through on-going investigation and collaborative discussion  N.8.A.5 Students know how to use appropriate technology and laboratory procedures safely for observing, measuring, recording and analyzing data.

C.C.S.D. Standards  6.11 The student will use an operational definition of ‘property’  6.12 The student will explain that some properties can be used to identify substances and some can be used to describe substances.  6.13 The student will classify substances using their properties.  6.14 The student will demonstrate the properties that can be used to identify matter: density, solubility, boiling point, melting point, freezing point, acidity, magnetism and conductivity.

Acids and Their Properties  Acid: Any compound that increases the number of hydronium ions, H 3 O +, when dissolved in water.  Hydronium ions form when a hydrogen ion, H + separates from the acid and bonds with a water molecule, H 2 O

Acids  Acids have a sour flavor.  Lemons and Limes are acidic, therefore they have a sour taste. WARNING: NEVER taste an unknown chemical. Many acids are corrosive which means they destroy body tissue, clothing and other things.  Most acids are poisonous.

Indicator  Indicator: A substance that changes color in the presence of an acid or base.  Litmus paper is commonly used in the lab. When an acid or base is added to the paper, it changes color.

Acids react with metals  Acids react with some metals to produce hydrogen gas.  For example, hydrochloric acid reacts with zinc metal to produce hydrogen gas.  2HCl + Zn→H 2 + ZnCl 2

Acids Conduct Electric Current  When acids are dissolved in water, they break apart and form ions in the solution. The ions make it possible for the solution to conduct an electric current.  Batteries are used to produce an electric current.

Uses of Acids  Sulfuric Acid- paper, paint, fertilizers  Nitric Acid-fertilizers, rubber, plastics  Hydrochloric Acid-separates metals, cleans swimming pools, etches glass.  Hydrochloric Acid is even found in your stomach!!!!

Bases and their Properties  Base: Any compound that increases the number of hydroxide ions, OH -, when dissolved in water.  For example, sodium hydroxide breaks apart to form sodium ions and hydroxide ions.  NaOH → Na + + OH -

Properties of Bases  Bases have a bitter flavor and slippery feel.  If you have ever accidentally tasted soap, you know the bitter taste of a base.  ATTENTION: Never touch, smell or taste an unknown chemical to identify it. Like acids, many bases are corrosive.

Bases conduct electric current  Solutions of bases conduct electric current because bases increase the number of hydroxide ions, OH -, in a solution.  A hydroxide ion is actually a hydrogen atom and an oxygen atom bonded together. The extra electron gives the hydroxide ion a negative charge.

Examples of Bases  Soaps  Bleach  Detergents  Baking soda  Like acids bases change the color of an indicator (litmus or pH paper)

The Strengths of Acids and Bases  Acids and Bases can be strong or weak.  The strength of an acid or base depends on the number of molecules that break apart when the acid or base is dissolved in water.

Strong and Weak Acids Strong Acids Hydrochloric Acid Sulfuric Acid Nitric Acid Weak Acids Acetic Acid Citric Acid Carbonic Acid

Neutralizing Acids and Bases  Neutralization reaction: The reaction of an acid and a base to form a neutral solution of water and a salt.  Acids and Bases neutralize one another!  The hydrogen (H + ) ions from acid, and hydroxide (OH - ) ions from a base react to form water, H 2 O, which is neutral.

pH scale  An indicator, such as litmus paper, can identify whether a solution contains an acid or base.  To describe how acidic or basic a solution is, the pH scale is used.  pH paper contains several different indicators.  pH: A value that is used to express the acidity or basicity (alkalinity) of a system.

pH scale  The pH of a solution is a measure of hydronium ion concentration in the solution.  A solution that has a pH of 7 is neutral (neither acidic nor basic). Pure water has a pH of 7.  Acidic solutions have a pH less than 7  Basic solutions have a pH more than 7

Resources  Interactions of Matter, Holt, Rinehart and Winston, USA, 2005, pages    ml ml    