pH and Titration

Purpose To “titrate” means to mix chemicals for the purpose of measuring one of the chemicals Acid/ Base titrations are done by mixing acids and bases. One is slowly added to the other until and “endpoint” is reached. – The “endpoint” often involves a rapid change in pH shown by an indicator – The “endpoint” occurs when moles acid = moles base – It is used to determine the moles or concentration of acid or base

Some formulas…. Neutralization: – Acid + Base  Salt + Water Concentration X = moles X / Liter solution – rearranged: moles = C*V When reacted completely (from stoichiometry) – Moles acid = moles base so… – CV (acid ) = CV (base)

What it looks like…an example Start with a known volume of acid (with an indicator added) AND A buret containing a volume of base whose concentration is known Base Acid Slooooowly add base to the acid All the time measuring pH pH meter The volume will increase a bit There will be a sudden change in pH The indicator will change color A pH probe can be used To measure the pH (in addition To the indicator)

What it looks like…graphing pH Volume Base Added Start with a volume of acid… Low pH Slowly add base… pH rises More Base More Acid At the “endpoint”, the amount (moles) of acid = amount (moles) base

pH Volume Base Added Initial pH pH at endpoint The endpoint The important points 1)Initial volume of acid 2)Concentration of base 3)pH at initial volume of acid 4)pH at endpoint 5)Volume of base at endpoint