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Chemistry: Acids, Bases & The pH Scale

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Kara Gillivan

on 7 February 2013

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Transcript of Chemistry: Acids, Bases & The pH Scale

Chemistry: Acids, Bases & The pH Scale What Are The Properties of Bases? What Ions Do Acids and Bases Form in Water? What Are the Properties of Acids? An acid reacts with metals and carbonates, tastes sours, and turns blue litmus paper red A base tastes bitter, feels slippery, and turns red litmus paper blue Acids in Solution What Are the Products of Neutralization? When you mix an acid and a base, it results in salt water. If you tested the pH of the mixture, it would be close to 7 or neutral which is why this reaction is called neutralization
A salt is any ionic compound that can be made from a neutralization reaction. A salt is made from the positive ion of a base and the negative ion of an acid
Example: Sodium chloride (table salt)
Neutralization reaction =
NaOH + HCl --> H2O + Na+ +Cl-
Salt Formula = NaCl Measuring pH To determine the strength of an acid or a base, chemists use a scale called pH. The pH scale ranges from 0 to 14
It expresses the concentration of hydrogen ions in a solution
The most acidic substances are found at the low end of the scale, while basic substances are found at the high end
A low pH tells you that the concentration of hydrogen ions is high and the concentration of hydroxide ions is low. A high pH tells you that the opposite is true
7 is neutral Reactions With Metals Acids react with certain metals to produce hydrogen gas
When they react, the metals seem to disappear in the solution
This is one reason why acids are described as corrosive, meaning they wear away other materials Reactions With Carbonates Acids react with carbonates to produce carbon dioxide gas
Some objects that contain carbonate ions are seashells, eggshells, chalk, and limestone Sour Taste Citrus fruits, such as lemons, grapefruit, and oranges all contain citric acid
Other foods such as vinegar and tomatoes can contain acids
Although sour taste is a characteristic of many acids, it is not one you should use to identify an acid Reactions With Indicators Chemists use indicators to test for acids, litmus paper is an example of an indicator, a compound that changes color when it comes in contact with an acid
Acids turns blue litmus paper red Bitter Taste Some foods that include bases are almonds and cocoa beans Slippery Feel Many soaps and detergents contain bases
Strong bases can irritate your skin Reactions of Bases Bases do not react with metals or carbonates. This lack of a reaction can be useful in identifying an unknown substance
Bases react with acids in a chemical reaction called neutralization, in which acids and bases deactivate one another Reactions With Indicators Bases turn red litmus paper blue (Bases turn litmus paper Blue) Properties of Acids and Bases Properties Acids Bases Reaction with Metals Reaction with carbonates Taste Reaction with litmus paper Uses Produces hydrogen gas No reaction Produces carbon dioxide gas No reaction Sour Bitter Blue litmus paper turns red Red litmus paper turns blue Stomach acid, many foods Cleaning products In a solution with water, most acids separate into hydrogen ions and negative ions
A hydrogen ion (H+) is an atom of hydrogen that has lost its electron and has a positive charge
For example: hydrochloric acid --> hydrogen ions and chloride ions form
HCl --> H+ + Cl-
The formulas for acids usually begin with the letter H
Example:
Nitric Acid = HNO3 Sulfuric Acid = H2SO4 Acetic Acid = HC2H3O2
Acids can be strong or weak. Strength refers to how well the acid separates into ions in water
The molecules in a strong acid separate to form hydrogen ions in solution
In a weak acid, very few particles separate to form ions in solution Bases In Solution Most bases are made of hydroxide
ions combined with positive ions and
produce hydroxide ions in water
The hydroxide ion (OH-) is a negative
ion made of oxygen and hydrogen
When some bases dissolve in water, they separate into positive ions and hydroxide ions
Example: Sodium hydroxide --> sodium ions and hydroxide ions form
NaOH --> Na+ + OH-
Example of bases: notice they do not all have OH in their formula
Potassium hydroxide = KOH
Calcium hydroxide = Ca(OH)2
Ammonia = NH3
Calcium oxide = CaO ACIDS high concentration of H+ low concentration of OH- BASES high concentration of OH- low concentration of H+ Hydrochloric Acid-0 Lemon Vinegar Banana-4.8 Pure Water Blood-7.4 Baking soda-8.3 Antacid Drain cleaner
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