titrations

1. titrations The big idea, Glassware and techniques

2. Using one solution of known concentration and one unknown concentration to find... • …..The concentration of the unknown solution.

3. Lets think…. • If we have a measured amount of the known solution – what can we calculate? • The amount of moles in that volume. • Why is this important? • Stoichiometry....this known (calculated) amount of moles will react with moles in the unknown solution according to the balanced equation. • Example: • Mrs VW has made us a solution of Na2 CO3 using 2 g of solid in 200 mL of water. • Calulate the concentration of this solution:

4. Example: • Mrs VW has made us a solution of Na2 CO3 using 2 g of solid in 200 mL of water. • Calculate the concentration of this solution: • n = m/Mr • C = n/v • If we take exactly 20 mL pipette of this solution, add some indicator and react it with some acid a few drops at a time, from a burette what will happen?

5. EXAMPLE continued • We will always use the same amount of acid as the same number of moles will react every time. _________________ • How many moles of Na2 CO3 was in the 20 mL? • n = c x V • Write a balanced equation for the acid + the carbonate. • _______________ + _________________  ______________ + CO2 + H2 O • Use the mole ratio from the equation to calculate the number of moles of acid used • n = k/u x n(Na2 CO3 )=

6. Now we know the number of moles that reacted we can calculate the concentration of HCl. • C = n/v • What’s the point of this technique? • We can use it to calculate concentration or amount of an unknown substance in any solution which can react with another chemical. • Eg: amount of vitamin C in fruit juice

7. pipette • Wash with distilled water • Wash with solution you will be filling it with • Attach pipette filler carefully • Draw up solution past the line of the pipette • Quickly remove pipette filler and place thumb over top. • Hold at eye level and rotate pipette so that the solution is released a small amount at a time until the meniscus is level with the line • Allow to flow into conical flask and touch end gently to side of flask when finished • Do not blow or tap pipette on glass.

8. Pipette challenge • In groups you need to deliver exactly 20 mL of fluid of 6 different colours into 6 conical flasks – red, orange, yellow, green, blue, purple. • You have the following solutions: • Water (from tap) • Hydrochloric acid • Acetic acid • Ammonia • Sodium hydroxide

9. Burette • Wash with distilled water • Wash with solution you will be filling it with. • Fill past zero using a funnel and rotate on side to ensure no air bubbles • Remove funnel and discard excess solution over zero • Take reading to 2 decimal places at eye level from bottom of mensicus

10. Conical flask • Wash with distilled water • Fill with solution from pipette • Add indicator • Wash solution down from sides of flask during titration with distilled water as well as from end of burette • Swirl in left hand and hold burette tap in right hand • Place a white tile or white paper underneath so you can observe colour change – don’t go too far!