1-making standard solutions and titrations

Question 1

method for making a standard solution (7)

Answer 1

1.weigh sample bottle containing the solid on a 2dp balance
2. transfer solid to beaker and reweigh sample bottle
3.record difference in mass
4.add 100cm3 distilled water and stir with glass rod until all solid has dissolved
5.pour solution into a volumetric flask with a funnel and add washings from beaker
6.make up to the 250cm3 mark with distilled water- use dropping pipette for the last few drops
7.invert flask several times to ensure uniform solution

Question 2

what 3 accuracy measures should take place when making standard solutions

Answer 2

-sometimes the solid may not fully dissolve in cold water so the beaker can be heated gently until all the solid has dissolved
-rinse the glass rod into the washings to make sure any solution lost in transfer is kept to a minimum
-don’t overshoot the graduate mark so use a dropping pipette for the last few drops

Question 3

method for doing a titration (8)

Answer 3

1.pour 100cm3 of the standard solution into a beaker
2.attach the filler to the pipette and rinse it with the standard solution
3.pipette out 25.0cm3 of standard solution into a conical flask (flask should be rinsed with deionised water)
4.add 4 drops of indicator to flask and record initial colour
5.use a funnel to rinse the burette with the solution, then fill it. Record initial burette reading
6.titrate the standard solution from the pipette to the beaker, whilst swirling
7.titrate dropwise near endpoint until the colour change so you get a precise volume
8.record final burette reading. Repeat until you get concordant results

Question 4

what 4 accuracy measures should take place when doing a titration

Answer 4

-make sure there are no air bubbles in the jet or the titre volume will be bigger than expected
-a flask is used instead of a beaker as it is easier to swirl and doesn’t spill contents
-don’t add too much indicator as it is acidic and will change ph
-rinse the insides of the flask with deionised water to ensure all the reagents are reacting. This water doesn’t change the moles of each reactant so it doesn’t affect results