Lecture 7: Acid and Bases

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1 Lecture 7: Acid and Bases
Chemistry – SPRING 2017 Course lecturer : Jasmin Šutković

2 What is an acid? An acid is a solution that has an excess of H+ ions. It comes from the Latin word acidus that means "sharp" or "sour". The more H + ions, the more acidic the solution.

3 Properties of an Acid Tastes Sour Conduct Electricity
Corrosive, which means they break down certain substances. Many acids can corrode fabric, skin,and paper Some acids react strongly with metals Turns blue litmus paper red Picture from BBC Revision Bites

4 Uses of Acids Acetic Acid = Vinegar
Citric Acid = lemons, limes, & oranges. It is in many sour candies such as lemonhead & sour patch. Ascorbic acid = Vitamin C which your body needs to function. Sulfuric acid is used in the production of fertilizers, steel, paints, and plastics. Car batteries

5 What is a base? A base is a solution that has an excess of OH- ions. Another word for base is alkali. Bases are substances that can accept hydrogen ions

6 Properties of a Base Feel Slippery Taste Bitter Corrosive
Can conduct electricity. (Think alkaline batteries.) Do not react with metals. Turns red litmus paper blue.

7 Uses of Bases Bases give soaps, ammonia, and many other cleaning products some of their useful properties. The OH- ions interact strongly with certain substances, such as dirt and grease. Chalk and oven cleaner are examples of familiar products that contain bases. Your blood is a basic solution.

8 Acid – Base Reactions A reaction between an acid and a base is called neutralization. An acid-base mixture is not as acidic or basic as the individual starting solutions.

9 Acid – Base reactions Each salt listed in this table can be formed by the reaction between an acid and a base.

10 Acids: Acid-Base Reactions HCl  H+ + Cl-
Ionize in H2O, causes increase in H+ ions. H+ ions are bare protons. Acids are proton donor Reacts with some metals to produce H2 Dissolves carbonate salts, releasing CO2 HCl  H+ + Cl-

11 IONIZATION Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or ions.

12 What mean actually strong and weak acid/base?
The terms "strong" and "weak" do NOT refer to the concentration of the acid or base, but instead, refer to whether the acid or base dissociates completely in water.

13 Examples of strong acids
For strong acids, try to remember them, there are 6 : Strong acids: HCl Hydrogen chloride HBr Hydrogen bromide HI Hydrogen iodide HClO4 Perochloric acid HNO3 Nitric acid H2SO4 Sulfuric acid

14 Bases Bases: Substances that increase the OH- when added to water. (NaOH) Strong bases: Any groups in 1A or 2A elements with OH elements with O elements and NH2

15 Definitions of Acids and Bases
 Brønsted – Lowry definition of acids and bases A more general definition of acids and bases – An acid is any substance that can donate a proton. – A base is any substance that can accept a proton.

16 Strengths of Acids and Bases
Strong acids react essentially completely with water to give H+ and the corresponding anion. Strong bases dissociate essentially completely in water to give OH– and the corresponding cation. Both strong acids and strong bases are strong electrolytes.

17 Some Properties of Acids and Bases
Acid Properties Sour taste Turn blue litmus red pH < 7 Base properties Bitter taste Turns red litmus blue pH >7 slippery

18 The Hydronium Ion When a strong acid dissolves in water, the proton that is released is transferred to a water molecule that acts as a proton acceptor or base, so the Resulting molecule is H3O+ ion is called the hydronium ion. Substances that can behave as both an acid and a base are said to be amphoteric.

19 An acid reacts with a metal hydroxide to form a salt plus water.
Neutralization reactions Acid + Base Neutralization HBr(aq) + NaOH(aq) H2O(l) + NaBr(aq) Products of a neutralization reaction have none of the properties of an acid or a base. An acid reacts with a metal hydroxide to form a salt plus water.

20 The pH scale pH is a measure of how acidic or basic a solution is.
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. Pure water has a pH of 7. Basic solutions have pH values above 7.

21 The pH scale pH is defined as the negative base-10 logarithm of the hydrogen ion concentration pH = – log [H+] or [H+] = 10-pH Hydrogen ion concentration in pure water is 1 x 10-7 M at 25ºC; the pH of pure water is – log [1.0 x 10-7] = 7.00. pH decreases with increasing [H+] — adding an acid to pure water increases the hydrogen ion concentration and decreases the hydroxide ion concentration. Adding a base to pure water increases the hydroxide ion concentration and decreases the hydrogen ion concentration—pH increases with decreasing [H+].