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pH,Acidic and Basic Solutions
Acids
• Acids are substances that release positively charged hydrogen ions, H+, in the water.
• H+ will combine with water releasing a positively charged ion called hydronium (H3O)+
HCl + H2O -----> (H3O)+ + Cl-
Bases
• Bases are substances that release negatively charged hydroxide ions, OH-, in the water.
• NaOH +H2O ---------> Na+ + OH- + H2O
Strengths of Acids and Bases
• The strength of an acid depends on how easily the acid will release H+ (hydrogen) ions when in water
• The strength of a base depends on how easily the base will release OH- (hydroxide) ions when in water
Indicators
• Indicators are compounds that react with acidic and basic solutions and produce certain colors, depending on the solution’s pH.
• Indicators help you determine the pH of a solution.
*Litmus paper is an indicator
It shows if a substance is an acid or a base:Red litmus paper in a base solution turns blueBlue litmus paper in an acid turns red
*Universal Indicator33
Gives you more information than the Litmus paper because gives you the pH value of the substance
pH and pH Scale
pH is a measure of how acidic or basic a solution is and depends on the concentration of hydronium and hydroxide ions.“pH stands for percentage hydrogen”
pH and pH Scale
• The pH scale ranges from 0 to 14.
• Acidic solutions have pH values below 7.
• A solution with a pH of 0 is very acidic.
• A solution with a pH of 7 is neutral.
• Basic solutions have pH values above 7.
Mini Lab 1:Litmus paper
• In groups.
• Each group has 2 substances ( vinegar and ammonia), 2 strips of red litmus paper and 2 strips of blue litmus paper.
• Dip one red strip and one blue inside each one of the substances and record your results on a table.
Mini Lab 1:
Litmus paper Ammonia Soda
Red color ? color ?
Blue color ? color ?
Acid or Base? ? ?
Mini Lab:
• Write a paragraph explaining why you obtained such results and if the substances you tested are acids or bases .
• Explain what is the role of the paper you used during the experiment and why did it changed color.
Mini Lab 1:
Litmus paper Ammonia Soda
Red Turn blue Stay red
Blue Stay blue Turn red
Acid or Base? base acid
*Properties of Acidic Solutions
-sour taste-can conduct electricity because it has ions-are corrosive, which means they break down -certain substances. Many acids can corrode fabric, skin, and paper.
-react strongly with certain metals.
Uses of Acids
Acetic Acid - vinegar and salad dressings
Citric Acid in limes, lemons and oranges
Ascorbic acid – vit C
Sulfuric acid - fertilizers, steel, paints, and plastics.Acids – batteries
Properties of Basic Solutions
Slippery
Bitter taste
Bases are corrosive.
can conduct electricity ( have ions)
Basic solutions are not as reactive with metals as acidic solutions are.
Uses of Bases
• soaps, ammonia, and many other cleaning products
• Chalk is basic
• Blood is basic
Neutralization
*Neutralization is the chemical reaction of an acid with a base. Ex:
It is a chemical reaction because new substances are being formed ( salt and water)
*How does neutralization occur?
Recall that every water molecule contains two hydrogen atoms and one oxygen atom.
The reaction of a base and an acid results in water and a salt . Water has a neutral pH.It is called neutralization because the acid and thebase are not there anymore…….
HCl + NaOH NaCl + H20 ( neutral)
Lab:
• Creating a pH scale