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NEUTRALIZATION AND
TITRATION
LET’S REVIEW NEUTRALIZATION Acid + Base Salt + Water Salt = ionic compound made up of the
anion from an acid and the cation from a base.
REMEMBER: when any strong acid reacts with any strong base in the mole ratio from a balanced chemical equation, a neutral aqueous solution of a salt is formed.
Note: reactions between acids and bases of different strengths usually don’t result in neutral solutions.
HOW CAN WE MONITOR A NEUTRALIZATION REACTION? 1. pH probe 2. Indicator
An indicator is usually a weak monoprotic acid with a complex organic structure.
HIn(aq) ↔ H+(aq) + In-
(aq)
Color 1 Color 2Phenolphthalein:
(You do not need to know this structure)
ANTACIDS? What are they? How do they work?
Antacids are supposed to decrease the amount of hydrochloric acid in the stomach by reacting with excess acid (ie. they neutralize your stomach acid). They are used in the treatment of gastric hyperacidity and peptic ulcers. Some of the ingredients in antacids are: Magnesia (MgO), milk of magnesia (Mg(OH)2, calcium carbonate (CaCO3), sodium bicarbonate (NaHCO3), dihydroxyaluminum sodium carbonate (NaAl(OH)2CO3), aluminum hydroxide gel (Al(OH)3).
ANTACIDS: What’s going to happen when I put the
TUMS (main ingredient is CaCO3) in the acid?
What if I add phenolphthalein?
What if I add bromythol blue?
What if I add bromocresol green?
LETS LOOK AT A PROBLEM WITH A DIPROTIC ACID: What volume of 0.250 M H2SO4(aq) is needed to
react completely with 37.2 mL of 0.650 M KOH(aq)? Step 1: Balanced equation H2SO4(aq) + KOH(aq) K2SO4(aq) + H2O(l)
Step 2: amount (mols) of KOH= 0.650 mol/L x 0.0372 L = 0.02418 mol KOH
Step 3: mols H2SO4 (reacts with KOH in 1:2 ratio)=
0.02418 mol KOH x ( ) = 0.01209 mol H2SO4
2 2
LETS LOOK AT A PROBLEM WITH A DIPROTIC ACID:
Step 4: Volume H2SO4(aq)
= = 0.04836 L
Therefore, the volume of H2SO4(aq) required is 48.4 mL.
NOW: If you are more comfortable working with this equation, go ahead! Just be careful with your mole ratios!
CAVA = CBVB
H2SO4(aq)
2
OK, YOU DO ONE: What volume of 0.150 M hydrochloric
acid is needed to neutralize 80.0 mL of 0.0045 M calcium hydroxide?
TITRATIONS
Moving On…
WHAT’S A TITRATION? It’s a method chemists use to determine
the concentration of a solution by observing it’s quantitative reaction with a solution of known concentration In other words, if we have some volume of
acid and we want to determine it’s concentration, we can “titrate” it with a solution of base of which we know the concentration (or vice versa)
TITRATIONS:
Titrant: what we put in the buret
IF USING AN INDICATOR
Endpoint = point at which your indicator (just) changes color
TITRATION CURVES Graph of the pH of an acid (or base) vs
the volume of titrant base (or acid) You need to know what these types of
titration curves look like:Strong acid + strong baseWeak acid + strong BaseWeak base + strong acid
You do not need to know the curve for the titration of a weak acid with weak baseWhy? It’s complicated!
STRONG ACID + STRONG BASE
Strong acid + strong base titrations: equivalence point is always pH 7
Want an indicator that has an endpoint close to the equivalence point
WEAK ACID + STRONG BASE
Equivalence point is greater than pH 7
WEAK BASE + STRONG ACID
Equivalence point is less than pH 7
TITRATION LAB: http://www.mhhe.com/physsci/chemistry
/animations/chang_7e_esp/crm3s5_5.swf
http://wwwchem.uwimona.edu.jm:1104/software/titr.html
WE ARE ALMOST DONE ACIDS AND BASES!
Assignment for the remainder of class: In groups of 2-3, go online and find one of the
following: An article relating in acids and/or bases An application (industrial, medicinal, environmental,etc.)
of acids/bases A cool experiment relating to acids or bases
Prepare to give us the “gist” of what you discover in 2-3 minutes Need help? You could look at:
Natural buffer systems Acid-base chemistry and baking Acid rain Use of indicators (ex. medicine) Natural acid-base remedies (ex. bee/wasp stings) Acidic or basic drugs extracted from natural sources
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