Neutralization, Titration & Concentration

Neutralization

• For an acid to effectively neutralize a base (or vice versa) the number of moles of acid and base must be equal

Example• How many moles of sodium hydroxide are

required to neutralize 45.0 mL of a 0.120 mol/L H2SO4 solution?

• 1. Write a balanced equation.

2NaOH(aq) + H2SO4(aq) 2H2O(l) + Na2SO4(aq)

2. Determine the # of moles to be neutralized(calculate the number of moles of H2SO4)

2NaOH(aq) + H2SO4(aq) 2H2O(l) + Na2SO4(aq)

3. Use the coefficients to calculate the number of moles required for neutralization.

Extension

2NaOH(aq) + H2SO4(aq) 2H2O(l) + Na2SO4(aq)

4. If you used 30.0 mL of NaOH to neutralize the H2SO4, what is the concentration of the NaOH?

Titrations

• Requirements:– Standard an acid or base where you know the

[concentration]– Indicator a substance in which the completed

titration (change from acidic to basic or vice versa) will be demonstrated by a colour change

Titrations cont’d

• When the concentration of the acid and the base are equal, we have reached the “equivalence point”

• This is where:#Moles acid = #moles base

The end point is reached when one drop of titrate permanently changes the colour of the indicator

• Vinegar (aka Acetic Acid) was titrated with Sodium Hydroxide to determine the concentration of acetic acid present. A volume of 41.6 mL of 1.00 mol/L NaOH was required to neutralize a 50.0 mL sample of vinegar, indicated by a pink colour change. What was the concentration of the vinegar?

• 1. Write a balanced equation

2. Calculate the moles of the standard that were required to neutralize the unknown concentration of vinegar

* At the equivalence point the moles acid = moles base

NaOH(aq) + CH3COOH(aq) CH3COONa(aq) + H2O

3. Use the coefficients to figure out the mole ratio (notice it is 1:1 in this equation and therefore #moles CH3COOH = #moles NaOH

Calculate the concentration of CH3COOH

Example:• How many moles of sodium hydroxide are

required to neutralize 0.20 moles of nitric acid?

Example:• How many millilitres of 0.45 mol/L HCl solution

must be added to 25.0 mL of a 1.00 mol/L KOH solution to make a neutral solution?