As 2014 WAEC May/June and NECO June/July are approaching, we at MySchoolGist have decided to expose students to information that will make them have better grades in their exam without involving in any form of examination malpractices.
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So today, we want to publish another post that will help science students preparing for the 2013 WAEC May/June exam. We want to share a Titration Guide we culled from Wikihow.com to help 2013 WAEC May/June candidates learn about how to prepare a simple titration.
What is Titration?
A titration is a technique used in chemistry to help determine the concentration of a reactant mixed in with an unknown. When done correctly and carefully, a titration will yield very precise results. Here’s how to perform one.
1: Obtain the items listed in the “Things You’ll Need” section below.
2: Rinse and purge your burette.
3: Clean and rinse all glassware with tap water (DI H2O if available is better), using some detergent if necessary. Be very careful with burets, as they are very fragile. Always hold them with two hands.
4: Rinse all glassware with distilled water to lower the chances of contamination.
5: Measure out a precise amount of analyte (the reactant mixed in with the unknown).
6: Fill your beaker or Erlenmeyer flask with a small amount of distilled water.
7: Rinse the analyte into your beaker or Erlenmeyer flask, thus making sure all of the analyte is in the beaker.
8: Put a small amount (4-5 drops) of the appropriate color indicator into the beaker.
9: Agitate the beaker’s contents by swirling the beaker.
10: Fill the burette with an excess amount of titrant (chemical that reacts with the analyte). The titrant should be in an aqueous form.
11:Clamp the burette carefully to a burette stand. The tip of the burette should not be touching any surfaces.
12 : Place the beaker under the burette.
13: Record the initial volume of the burette at the meniscus (the lowest part of the dip in the liquid).
14: Turn the stopcock of the burette (valve near the tip) vertical, so that titrant is added to the beaker. Only let a small amount of the titrant out. A color change should occur. Agitate the beaker until the color disappears.
15: Repeat the above step until the color persists slightly (you may barely notice it, so be careful & go extremely slowly).
16 : Record the volume of the burette.
17: Add titrant drop by drop as you near the endpoint.
18 :Agitate the beaker’s contents after every drop.
19: Stop when you’ve reached endpoint, which is the point when the reactant within the analyte has been completely neutralized. You can tell you’ve reached the endpoint with a colour change, depending on which indicator you chosen to use.
20: Record your final volume.
21: Past endpoint – point of no return. Add drops of titrant until you pass endpoint. At this point, the beaker’s contents should be entirely the color of the color indicator when titrant is added.
22: Clean up by wiping away all standing water.
23: Dispose of the chemicals used in a labeled waste container.
24: Calculate the concentration of the reactant within the analyte using the data gathered.
Have your eyes at the same level while reading the volume from the burette – if your eyes are at a diff level each time your readings will not be as accurate.
Record the volume of the burette to one digit past what is given (ex: buret has readings to the nearest tenth; take your observation down to the nearest hundredth).
Calculations of the concentration should be done to the appropriate number of sig figs.
Tips for better accuracy:
put a small beaker over the top of the burette, especially if you are titrating with NaOH; if it is left in contact with the air some of the OH will bond w/ water molecules and it will disturb the molarity of the NaOH solution.
Endpoint is extremely easy to overshoot, if you’re not careful and observant. When you have the slightest feeling you’re approaching endpoint, start counting drops, and go extremely slowly.
keep a watchglass over the flasks of water & the unknown; the time they are left sitting out while you are doing your other titrations can change the molarity.
Handle the burette with care – they are easily broken.
Remember to take out the filter funnel after you have done filling the burette with the titrant as it can prevent your titration from being perfectly accurate.
Be sure to rinse all of the analyte into the beaker. Any left in the weighing boat/container will result in miscalculations.Don’t rinse any of the chemicals down the sink; put into an appropriate, labeled waste container.