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ACIDS & BASES. Chapter 5.1. 5.1 Learning Outcomes. Differentiate between acids, bases and salts with respect to chemical formula, name, and properties. Identify acids and bases using indicators (e.g., methyl orange, bromthymol blue, litmus, phenolphthalein, indigo carmine).
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ACIDS & BASES Chapter 5.1
5.1 Learning Outcomes Differentiate between acids, bases and salts with respect to chemical formula, name, and properties. Identify acids and bases using indicators (e.g., methyl orange, bromthymol blue, litmus, phenolphthalein, indigo carmine). Explain the significance of the pH scale, with reference to common substances. Recognize the names and formulas of common acids (ie: Hydrochloric acid, suphuric acid, nitric acid, acetic acid).
5.1 Vocabulary Methyl orange Methyl red Neutral Neutralization pH indicator pH scale Phenolphthalein Salts Acidic Acids Bases Basic Bromothymol blue Concentration Indigo carmine Litmus
Interesting Facts The Scorpion is most notable for "The sting in the tale" the venom is stored in a bulb like sack almost at the end of the tail and it is administered to the unlucky victim through a very sharp needle point sting. The venom paralyses its quarry in a second or less, then the Scorpion squirts acid from its mouth onto it to dissolve the tissues before sucking up the slushy remains. Only 20 species of Scorpion can hurt or kill a human with a sting. The most dealdy of all is the 'Death Stalker‘. It is found in the deserts of Iraq, Iran, and other neighbouring countries. It takes up to 12 hours to die after a sting. First you sweat, then you get dizzy and get severe pain in your joints. Next the fever starts, and that leads to convulsions, muscle spasms and finally coma and death.
Interesting Facts Bee stings are acidic with a pH of 3.5. Along with the acid, the venom that is released by a wasp or hornet also contains a pheromone which alarms all other wasps in the area and invites them to join the attack on the victim. It is meant to be a signal to all wasps to come and help. OUCH!! Fire Ants are very aggressive and will attack anything that disturbs their mound. After firmly grasping the skin with its jaws, the fire ant arches its back as it inserts its rear-end stinger into the flesh, injecting venom from the poison sac. It then pivots at the head and typically inflicts an average of seven to eight stings in a circular pattern. Fire ant venom has a very high concentation of toxins, which are responsible for the burning pain characteristic of fire ant stings.
ACIDS & BASES • Many familiar compounds are acids or bases. • Lemon juice, soap, oranges, pop… • Acids and bases can be very dangerous. • Both can be very corrosive. • NEVER try to identify an acid or base by taste or touch! See pages 220 - 222 (c) McGraw Hill Ryerson 2007
ACIDS & BASES • The strength of acids and bases in measured on the pH scale. • pH below 7 = acidic • pH above 7 = basic • pH 7 = neutral • 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acids Neutral Bases See pages 220 - 222 (c) McGraw Hill Ryerson 2007
ACIDS & BASES [ H+] Acids release __________ into a solution. Bases release _________ into a solution. [OH-]
pH SCALE [ H+] • pH is the concentration of ____ expressed as a logarithm. Every change in the pH scale of one unit is a change in ______ times the concentration of H+. Example: • pH 4 is 10X more acidic than pH 5. • pH 3 is 1000X more acidic than pH 5. 10
Litmus paper, pH paper, & neutralization animations http://www.bgfl.org/bgfl/custom/resources_ftp/client_ftp/ks3/science/acids/index.htm
ACIDS pH of 0 to 6.9 Contribute H+ ions into a solution Turn litmus paper RED Conduct ELECTRICITY Produce H+ gas (when added to some metals) Are CORROSIVE
ACIDS • Acids often behave like acids only when dissolved in water. • Therefore, acids often are written with symbol (aq) = aqueous = water. • The chemical formula of an acid usually starts with hydrogen (H). • HCl(aq) = hydrochloric acid, HNO3(aq) = nitric acid • Acids with a carbon usually have the C written first. • CH3COOH(aq) = acetic acid See pages 225 - 226 (c) McGraw Hill Ryerson 2007
Sulfuric acid is used in batteries. ACIDS • Naming acids: If you know a compound’s chemical formula, you may be able to identify whether it as an acid. • Hydrogen + …-ide = hydro…ic acid • HF(aq) = hydrogen fluoride = hydrofluoric acid • Hydrogen + …-ate = …ic acid • H2CO3(aq) = hydrogen carbonate = carbonic acid • Hydrogen + …-ite = …ous acid • H2SO3(aq) = hydrogen sulphite = sulphurous acid See pages 225 - 226 (c) McGraw Hill Ryerson 2007
BASES pH of 7.1 to 14 Donate [OH]- ionsinto a solution The hydroxide [OH-]group is neutralized by a hydrogen ion and water is formed. Turns litmus paper BLUE Conduct ELECTRICITY Are Slippery Are CAUSTIC
BASES • Bases often behave like bases only when dissolved in water. • Therefore, bases often are written with symbol (aq) = aqueous = water. • If you know a compound’s chemical formula, you may be able to identify it as a base. • The chemical formula of a base usually ends with hydroxide (OH). (c) McGraw Hill Ryerson 2007
BASES • Bases can be gentle or very caustic. • Examples of common bases: • NaOH(aq) • Mg(OH)2(aq) • Ca(OH)2(aq) • NH4OH(aq) See page 227 (c) McGraw Hill Ryerson 2007
Why is it Important to Maintain pH? • The pH of almost all living systems is between pH ________. Maintaining the proper pH then is vital living systems. • pH is very important to the environment as well: • acid rain • agriculture 6 - 8
Why is it Important to Maintain pH? Hydrangea in acidic soil Hydrangea in basic soil
pH INDICATORS • The pH of acids and bases cannot be determined by sight. • Instead, pH is measured by other chemicals called indicators OR by a pH meter that measures the electrical conductivity of the solution. • pH indicators change colour based on the solution they are placed in. • Litmus paper is the most common indicator. • There are 2 colours of litmus paper: • Blue = basic (pH above 7) • Red = acidic (pH below 7) Litmus paper (c) McGraw Hill Ryerson 2007
pH INDICATORS • A universal indicator contains many indicators that turn different colours at different pH values • can be in liquid form, or on paper strips like litmus. • Indicators change colour at different pH values, so different indicators are used to identify different pH values. • Bromothymol blue for pH 6 – 7.6, phenolphthalein for pH 8.2 – 10. • Many natural sources, such as beets, blueberries, cabbage, pansy flower petals... are also indicators. See pages 223 - 224 (c) McGraw Hill Ryerson 2007
pH INDICATORS Cabbage Juice paper in baking soda (BASE) Cabbage Juice paper in lemon juice (ACID)
Production of Ions • Acids and bases can conduct electricity because they release ions in solution. • Acids release hydrogen ions, H+ . • Bases release hydroxide ions OH–. • The pH of a solution refers to the concentration of HYDROGEN ions it has. • Square brackets are used to signify concentration, [H+], [OH–] • High [H+] = low pH, very acidic • High [OH–] = high pH, very basic See page 228 (c) McGraw Hill Ryerson 2007
Production of Ions • A solution cannot have BOTH high [H+] and [OH–]; they cancel each other out and form water. • This process is called neutralization. • H+ + OH– H2O OR H+ + OH– HOH See page 228 NEUTRALIZATION: http://www.youtube.com/watch?v=_P5hGzA6Vb0&feature=related
In water, the concentration of H+ is equal to the concentration of OH-. By definition, pure water is ______________________ A solution is ACIDIC if the _______________ A solution is BASIC if the ________________ [ H+] = [OH-] NEUTRAL [ H+] > [OH-] [ H+] < [OH-]
Litmus paper, pH paper, & neutralization animations http://www.bgfl.org/bgfl/custom/resources_ftp/client_ftp/ks3/science/acids/index.htm
See page 229 (c) McGraw Hill Ryerson 2007
