Acids & Bases

Goals To determine the difference between Acids & Bases Discuss the importance of studying Acids & Bases

HCl(g) NaOH(s) When an IONIC compound is placed in water, it will break apart into two ions. If one of those ions is H+... The solution is acidic. If one of the ions is OH-... The solution is basic.

Acidic solution Alkaline solution

Formulas - Acids In general, acids are identified by the hydrogen in the front of its chemical formula. For example, the formula for hydrochloric acid is HCl Others are: Sulfuric acid H2SO4; Carbonic acid H2CO3; and nitric acid HNO3. Some exceptions to this rule are some organic acids—such as acetic acid (CH3COOH)—have their formulae designated according to their structure.

Formulas - Bases Bases can often be identified by the OH term in the end of their chemical formula, as seen in sodium hydroxide NaOH, magnesium hydroxide Mg(OH)2 and potassium hydroxide KOH. There are some exceptions to this rule: ammonia gas NH3 Some organic acids have formulae that make them look like bases. Acetic acid (CH3COOH) for example.

The Arrhenius theory: Acids dissolve in water to produce hydrogen ions, H+ (more corrrectly, the hydronium ion H3O+) Bases produce the hydroxide , OH- ions. This theory, while essentially correct, has been superseded by the Brønsted-Lowry theory

Characteristics - differences Acids Tastes sour Turns litmus paper red React with some metals to give off H2 gas. React with carbonates to produce CO2 gas pH of 0 – 7 Have an excess of H+ ions in solution. Bases Tastes bitter Turns litmus paper blue Feels slippery to the touch pH of 7 to 14 Have an excess of OH- ions in solution.

Characteristics - similarities Both conduct electricity Acids and bases react together to form salts and water only. The process is called neutralization NaOH + HCl H2O + NaCl Both acids and alkalis cause colour changes in certain substances called indicators, such as litmus:

Identifying Acids and Bases Acids have a ph from 0-7 Lower pH value indicates a stronger acid. Bases have a pH from 7-14 Higher pH value indicates a stronger base.

Definitions of Acids and Bases An acid is a substance that breaks into ions in an aqueous solution. A Base (alkaline) is a substance that breaks into ions in an aqueous solution. Note: aqueous solution is any solution where is the solvent.

Characteristics Of Acids Acids can be characterized by: A sour taste. It turns blue litmus paper red It tastes sour. Try drinking lemon juice (citric acid)

Characteristics of Bases A Base is characterized by: A bitter taste. (Milk of Magnesia) It feels slippery. (Soapy Water) It turns Red Litmus Blue.

Mini-quiz to check your understanding 1 Mini-quiz to check your understanding 1. What element is in most acids and bases? Water Hydrogen Sulfur

2. Which pH indicates the material is acidic? 5.0 7.0 9.0

3. Why should you be careful dealing with acids? They can eat your skin away They can cause an upset stomach They smell real bad

5. Which is a base? CH3COOH NaOH NaCl

6. What can a gardener do if the soil is too acidic? Add a base such as lime or chalk to reduce acidity Add lemon juice to reduce the acidity Add salt (NaCl) until the soil becomes a base

What is the pH scale? The pH scale measures how acidic or basic a solution is.

The pH scale The pH scale is the concentration of hydrogen ions in a given substance. “the power of Hydrogen”

Did we Miss something?? What happens when the pH of a substance is 7? Ans: A pH level of 7 indicates a Neutral Substance i.e: Water!

Test Your Knowledge What is the range of an ACID on the pH scale? Ans: 0-7 What is the range of a BASE and what is another name for a BASE? Ans: 7-14, Alkaline

Why Learn about Acids & Bases? What do you think is the pH level of Toronto tap water? The pH of a swimming pool must be checked periodically. Why? Is it important for Lakes & Rivers to maintain a certain pH?

Naming Acids Binary acids HF hydrofluoric acid HBr Hydrobromic acid HI HCl

Acids with polyatomic ions H2SO4 Sulphuric acid HNO3 Nitric Acid H2CO3 Carbonic Acid

Acid-Base Indicators Certain chemicals have the special property of appearing in different colours depending on the pH of the solution they are in. Such chemicals are known as acid-base indicators A couple of drops of indicator in a solution will indicate its pH.

Three commonly used indicators.

Neutralization Reactions What would happen if an acid and a base were mixed up? What would happen if a hydrogen ion (H+) from an acid reacted with a hydroxide ion (OH-) from a base? 

Neutralization - reaction of an acid and base forming a salt and water. HCl  +  NaOH    NaCl  +  HOH Salts - composed of the positive half of a base and the negative half of an acid. Question:   What acid and base react to produce each of these salts? CaSO4       NH4NO3       CaCl2