Is Dilution the Solution? Some industries produce acidic wastes. Do acids become harmless as they are diluted? How much H 2 O is needed to neutralize an acid? What other choice do we have?

In a neutral solution [H+] = [OH-] = 1.0 x mol/L the lower the pH, the more acidic the solution, [H + ] > [OH - ] the higher the pH, the more basic the solution, [H + ] < [OH - ] Recall…

Neutralization Equations Neutralization is a double displacement reaction which produces water and a soluble salt. HBr (aq) + NaOH (aq)  H 2 O (l) + NaBr (aq) ACID + BASE  WATER + SALT

Question: Write the chemical reaction when lithium hydroxide is mixed with carbonic acid. Step 1: write out the reactants LiOH (aq) + H 2 CO 3 (aq)  Step 2: determine products … LiOH (aq) + H 2 CO 3 (aq)  Li 2 CO 3 (aq) + H 2 O (l) Step 3: balance the equation 2LiOH (aq) + H 2 CO 3 (aq)  Li 2 CO 3 (aq) + 2H 2 O (l) lithium hydroxide + carbonic acid  lithium carbonate + water Writing neutralization equations When acids and bases are mixed, a salt forms NaOH + HCl  H 2 O + NaCl base + acid  water + salt Ca(OH) 2 + H 2 SO 4  2H 2 O + CaSO 4

Neutralization Net Ionic Equation for Neutralization H + + OH -  HOH or H 2 O When acids and bases ionize in water, the hydrogen ions (H + ) and the hydroxide ions (OH - ) are attracted to one another and combine to form water (HOH). The salt produced from the reaction is soluble in water and therefore becomes the spectator ions.

Neutralization When a base is added to an acid, 1 mole of the OH- ions react with one mole of the H+ ions, decreasing the concentration of H+ ions. This causes the pH to increase to 7. When an acid is added to a base, 1 mole of the H+ ions react with one mole of the OH- ions, decreasing the concentration of OH- ions. This causes the pOH increase and the pH to decrease to 7. Neutralization destroys the properties of acids and bases.

Titration the progressive addition of an acid to a base, or vice versa, drop by drop from a burette, until the neutralization has occurred Usually performed to analyse an unknown concentration of acid or base

Some Vocab… Titrant – a solution of known concentration (standard solution) dispensed from the burette. Burette – a graduated glass tube with a valve at the bottom used for titrations Pipette – a glass tube used for transferring small amounts of a solution very accurately

When is a titration finished? End point – the point at which the indicator changes colour during a titration We select an indicator based on the the desired equivalence point. Equivalence point – the point at which the number of moles of acid (H + ions) added equals the number of moles of base (OH - ions) present or vice versa. n base = n acid

Calculating Concentration If the concentration of one of the solutions is known (standard solution), the concentration of the second solution can be calculated using stoichiometry. ements/titration.swf titration demo ements/titration.swf

Acid and Base Stoichiometry A mL sample of vinegar requires mL of M sodium hydroxide to react with all of the acetic acid. What is the concentration of acetic acid (molarity) in the vinegar?