Acids, Bases & Salts

Introduction Chemicals may be classed as acids or bases. Things that are neither acids nor bases are neutral. Neutral solution = pure water pH measures how acidic or basic a solution is.

Acids Acid – any compound that produces hydrogen ions in solution (ex: hydrochloric acid, lemon juice, vinegar) Strong acids can burn skin and eyes and even dissolve metals! Ex: Hydrochloric acid HCL  H+ + Cl- When acids are in water, the H+ molecule breaks loose

Base Base – hydroxide (OH-) is dissolved in water (Ex: milk, baking soda, drain cleaner) Strong bases can burn skin & eyes Bases react more easily with protein than with metal and are often used for cleaning Ex: Sodium Hydroxide NaOH  Na+ + OH-

Neutralization Neutralization - Process of reacting an acid and a base to produce a neutral solution Ex: H+ + OH-  HOH (or H2O) If the quantities of acid and base are right, all the H+ and OH- combine and there will be no excess  then the solution will become neutral

Salts Salts – compounds produced by the neutralization between an acid and base Ex: Hydrochloric acid and sodium hydroxide HCl + NaOH  Na+ + Cl- + HOH

How do we determine the difference between and acid and a base??

pH Scale pH – a unit of measurement that indicates the concentration of hydrogen ions (H+) in a solution p - stands for potential H – stands for Hydrogen pH = the potential of a substance to attaract hydrogen ions pH Scale goes from 0-14 0-6 = Acidic 7 = Neutral 8-14 = Basic

pH Scale Each pH unit is 10 times as large as the previous one A change of 2 pH units means 100 times more basic or acidic x10 x100

pH Scale 0--------------7---------------14 Acid Neutral Base If the solution has a …… 0--------------7---------------14 Acid Neutral Base (*the closer to the end of the scale, the stronger the solution is) H+ Ion Concentration pH Acid or Base or Neutral High Concentration of H+ Low pH (0-6) Acid Low Concentration of H+ High pH (8-14) Base ------------- 7 Neutral

Indicators Indicators – a substance that changes color when the pH goes above or below a certain value Types of Indicators – Litmus paper Methyl Orange Phenolphalein pH Paper Digital pH meters

The paper is treated with chemicals that change color to show the pH. When the paper touches the substance being tested, it turns a specific color to tell if the substance is an acid or a base. How to use pH Paper: Dip the pH strip into the solution The pH paper will change color as it reacts to the pH of the solution Match the color of the strip to the color key on the cover of the container

Why is pH important? Fish can’t live if the pH is too high or too low Soil has to be in a certain pH range for plants to grow and stay healthy.

Why is pH important? Water that has too high or low pH contains harmful dissolved chemicals. Water plant operators keep a careful watch on the pH of our drinking water, to keep it safe. Heavy metals, such as lead, react to changes in pH. Environmental regulations require drinking water to remain within a specific pH range to prevent lead and other metals from dissolving out of pipes and containers and entering the water.