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titrations

titrations. The big idea, Glassware and techniques. Using one solution of known concentration and one unknown concentration to find. …..The concentration of the unknown solution. Lets think…. If we have a measured amount of the known solution – what can we calculate?

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titrations

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  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!

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