Acids • An acid is a substance that produces hydrogen ions(H+) when in solution with water • Water (H2O) is made up of even amounts of H+ and OH- ions. Water is NEUTRAL because of this. When an acid dissolves in water, this changes the amount of H+ ions. • Examples of acids include hydrochloric acid, citric acid, acetic acid (vinegar)
Properties of Acids • The more H+ ions it produces, the more acidic the solution • Strong acids are very dangerous. They have a high H+ concentration. • Weak acids are less dangerous. They have a low H+ concentration
Acids • Acids occur naturally in many fruits • Sore muscles and sour milk are cause by the same acid (lactic acid) • Acids add a tangy, sour flavours to foods and drinks • Some are deadly!
Bases • A base is a substance that produces hydroxide ions (OH-) when in solution with water. • When a base is added to water it increases the amount of OH- ions • Another word for basic is alkaline • Example: Sodium hydroxide (NaOH)
Properties of Bases • The more OH- ions it produces, the more basic (alkaline) the solution • Strong bases are as dangerous as strong acids. They have a high OH- concentration. • Similarly, weak bases are like weak acids with a low OH- concentration
Bases • Bases are bitter-tasting compounds • They have a slippery feel • Bases are in most soaps, drain and window cleaners. • They can be found in many pharmaceutical drugs • Some bases are deadly!
pH Scale • pH means “power of the hydrogen ion” • A pH scale is a measure of the acidity of a solution • In pH the “p” is always lower case, even at the start of a sentence.
pH scale • The pH scale has a useful range of numbers between 0 and 14. • A solution with a pH of 7 is neutral (like water) • Below pH 7, a solution is acidic • Above pH 7, it is basic
Paper testing • Paper tests like litmus paper and pH paper
pH meter • Tests the voltage of the electrolyte • Converts the voltage to pH • Very cheap, accurate • Must be calibrated with a buffer solution
pH indicators • Indicators are dyes that can be added that will change color in the presence of an acid or base. • Some indicators only work in a specific range of pH • Once the drops are added, the sample is ruined • Some dyes are natural, like radish skin or red cabbage
Neutralization • When an acid and a base react together their pH becomes neutral. Acid + base salt + water Ex: HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) • This is a double displacement!
ACID-BASENEUTRALISATION NeutralisationReaction: Acid + Base Salt + Water Ex: HCl + NaOH NaCl + H2O • The acid and base neutralise each other creating a salt and water • Must be equal concentrations of acid and base
Actually a Double Displacement Reaction! acid + base salt + water KNO3 + H2O HNO3 + KOH HF + NaOH NaF + H2O 2 HCl + Ca(OH)2 CaCl2 + H2O 2
1. Ba(OH)2 + H3PO4 2. HC2H3O2 + NaOH 3. H2SO4 + KOH 4. H2CO3 + NaOH 5. Na2CO3 + HCl