Is Dilution the Solution?Is Dilution the Solution?

Some industries produce acidic wastes. Do acids become harmless as they are diluted?

How much H2O is needed to neutralize an acid?

What other choice do we have?

In a neutral solution

[H+] = [OH-] = 1.0 x 10-7 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) H2O (l) + NaBr (aq)

ACID + BASE WATER + SALT

http://www.chem.ox.ac.uk/vrchemistry/chapter16/Movies/Neutralization.swf

Question: Write the chemical reaction when lithium hydroxide is mixed with carbonic acid.

Step 1: write out the reactantsLiOH(aq) + H2CO3(aq)

Step 2: determine products …LiOH(aq) + H2CO3(aq) Li2CO3(aq) + H2O(l)

Step 3: balance the equation2LiOH(aq) + H2CO3(aq) Li2CO3(aq) + 2H2O(l)

lithium hydroxide + carbonic acid lithium carbonate + water

Writing neutralization equationsWriting neutralization equationsWhen acids and bases are mixed, a salt forms

NaOH + HCl H2O + NaCl base + acid water + salt

Ca(OH)2 + H2SO4 2H2O + CaSO4

http://www.saskschools.ca/curr_content/chem30/swf/neutralize.swf

Neutralization

Net Ionic Equation for Neutralization

H+ + OH- HOH or H2O

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 = nacid

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.

http://web.fccj.org/~ksanchez/flash/Measurements/titration.swf titration demo

Acid and Base Stoichiometry

A 35.00 mL sample of vinegar requires 51.74 mL of 0.4298 M sodium hydroxide to react with all of the acetic acid. What is the concentration of acetic acid (molarity) in the vinegar?