Classifying Chemical ____________ COMPOUNDS Acids, Bases and Salts

Classifying Compounds We already know how to classify compounds based on the type of bond they form. Ionic: electrons transferred, ions made.(metal + non-metal) Covalent: electrons shared. (non-metal + non-metal) We can also classify compounds into many other categories Acids Bases Salts Organics Inorganics

Today’s Objectives Be able to distinguish acids and bases by looking at their: Properties Chemical formulas Learn about the pH scale How it is related to Acids and Bases Its significance How we use it Textbook Chapter 8 pages 205-206

Acids and Bases Some Common Acids: Citrus Juice-Orange, Lemon and Lime Vinegar Tomatoes Anything with a SOUR taste. We often add acids to our foods to improve taste and help us to absorb nutrients. CAUTION!!! Many Acids are CORROSIVE which means they can burn your skin. Never attempt to identify an acid by touch or taste!

Acids and Bases Some Common Bases: CAUTION!!! Eggs Baking Soda Soap Bleach Anything with a BITTER taste and/or a slippery feel. CAUTION!!! Many Bases are CAUSTIC which means they can burn your skin. Never attempt to identify a base by touch or taste! ***So if we can’t touch or taste compounds how do we know if they are acids or bases?

The pH Scale A number scale for measuring how acidic or basic a solution is. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH below 7 = acidic pH above 7 = basic pH 7 = neutral

What Do the Numbers Mean? Each decrease of 1 on the pH scale indicates 10X more acidic. For example, pH 4 is 10x more acidic than pH 5 pH 3 is 1000x more acidic than pH 6 pH ____ is 100x more acidic than pH 5 pH 1 is 10 000 000 000 000x more acidic than pH 14 3

What is pH really measuring? The pH of a solution refers to the concentration of its H+ ions. Remember: CONCENTRATION is the amount of substance (solute) dissolved in a given volume of solution. Square brackets are used to signify concentration, [H+], [OH–] High [H+] = low pH, very acidic High [OH–] = high pH, very basic Phet

More About pH If a substance has a lot of H+ ions then it has a low pH. If a substance has a lot of OH- ions then it has a high pH. If a substance has the same amount of H+ ions as it has OH- ions then it is NEUTRAL. Phet

pH Indicators The pH of acids and bases cannot be directly 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.

pH and Litmus Paper Litmus is the most common indicator, and is used on litmus paper. Two colours of litmus paper: Blue Litmus Paper Red Litmus Paper pH above 7 (basic) pH above 7 (basic) (stays blue) (turns blue) pH = 7 (stays blue) pH =7 (stays red) pH below 7 (acidic) pH below 7 (acidic) (turns red) (stays red) Memory device: BAR = BLUE + ACID  RED

Litmus Paper ACID BASE

pH Probes A pH meter uses electrical probes to measure how solutions conduct electricity. We said that acids and bases like to form H+ ions and OH- ions when in solutions and the concentration of these ions will determine a solution’s electrical conductivity.

More About ACIDS Acids readily react with metals to produce hydrogen gas We can also identify Acids by looking at their chemical formula. The chemical formula of an acid usually starts with hydrogen (H_). Acids with a carbon usually have the C written first. Acids often behave like acids only when dissolved in water and so they often have the subscript (aq) Acids conduct electricity because they release hydrogen ions, H+(aq)

Common Acids HCl(aq) = hydrochloric acid HNO3(aq) = nitric acid H2SO4 (aq) = Sulphuric acid CH3COOH(aq) = acetic acid

More About Bases We can also identify Bases by looking at their chemical formula. The chemical formula of a base usually ends with hydroxide (OH). Bases release hydroxide ions OH–(aq) Bases often behave like bases only when dissolved in water and so they often have the subscript (aq) Don’t readily react with metals

Examples of common bases NaOH(aq) – Sodium Hydroxide Mg(OH)2(aq) – Magnesium Hydroxide Ca(OH)2(aq) – Calcium Hydroxide NH4OH(aq) – Ammonium Hydroxide

BASES ACIDS pH less than 7, corrosive pH more than 7, caustic Litmus turns RED Litmus turns BLUE Conduct electricity (when dissolved in water) Chemical Formula starts with H Chemical Formula ends with OH React with metals to produce H2 gas Do not readily react with metals

Review We can classify Acids and Bases based on: Their pH Their colour change with indicators Their conductivity Their chemical formula Their reactivity

What About SALTS? What is a salt??? Salts are ionic compounds formed when acids and bases react. Salts are also produced when oxides or carbonates react with acids or when metals react with acids. Table salt, NaCl, is found in sea water, salt lakes or rock deposits. NaCl is only one kind of salt. A salt is made up of a positive ion from a base and a negative ion from an acid. Salts are found in many things: In batteries, explosives and fertilizers In multivitamins In many living cells