GEN CHEM 2 | Titration

Titration

• volumetric analysis

• common laboratory method to determine the concentration of an unknown solution

Titrant

• acid or base of known concentration that is added to the substance being analyzed

• placed in burette

Analyte

• substance that is being analyzed or unknown

• placed in flask

Burette

where titrant is placed

Burette clamp

holds burette above the flask

Stopcock

controls whether the titrant can flow into the flask

Flask

where analyte is placed

Initial Reading

the initial volume of the titrant in the burette

Final reading

• the final volume of the titrant in the burette once the end point is reached

• usually occurs when the indicator causes a color change

• initial is subtracted from the final volume to obtain the final

Acid-Base Titration

• determines the unknown acidic or basic substance through acid-base reaction

• involves strong/weak acids or bases

• determines the concentration of an acid or base, and whether it is strong or weak

Titration Curve

• graphical representation of how the pH of a solution changes when a base or acid is added

• follows a neutralization reaction

Equivalence Point

• which just an adequate reagent/titrant is added to react completely with a substance

• added titrant and analyte are chemically equal

• theoretical point

Endpoint

• point wherein solution changes color

• practical point

• detected using indicator

• may or may not coincide exactly with the equivalence point

Acid-base Indicators

• substance which change color or develop turbidity at a certain pH

• locate equivalence points and measure pH

• includes phenolphthalein, litmus, methyl orange, etc.

• must change over the vertical section of the curve where there is a large change in pH for the addition of a very small volume of alkali/base

Phenolnaphthalein

color changes from clear to pink at around pH = 9

Litmus

color changes from red to blue at around pH = 7

Methyl Orange

color changes from clear to pink at around pH = 4

Types of Titration Curves

• Strong Acid vs Strong Base

• Strong Acid vs Weak Base

• Weak Acid vs Strong Base

• Weak Acid vs Weak Base

Strong Acid vs Strong Base

• starts at a very low pH

• pH rises very slowly at first then shows a very steep jump

• equivalence point is around 7

• after eq. pt., pH is high

Strong Acid vs Weak Base

• starts at a very low pH

• pH rises but the curve is less steep

• equivalence point is < 7

• after eq. pt., pH is in the acidic and neutral range

Weak Acid vs Strong Base

• starts at a moderately low pH

• early in the titration, there is a buffer region where pH changes gradually

• equivalence point is above 7

• after the eq. pt, the pH becomes strongly basic

Weak Acid vs Weak Base

• starts at a moderate pH

• curve is smoother and less steep overall

• equivalence point clearly not at 7

• choosing an indicator is hard due to the less steep curve