Required Practical 1 Flashcards
What is a volumetric solution?
a solution you know the exact concentration of
How do you make a volumetric solution?
find out how many moles you need using mol = conc x vol, then work out how many grams you need using the formula mass = Mr x mol, place a weighing boat on a top pan balance and zero it, then weigh out the correct mass of solid, and tip into a beaker. then reweigh the weighing boat and subtract this value from the initial one to find the exact mass of solid added. then add distilled water to the beaker and stir with a stirring rod until all solid has dissolved, and transfer solution to a 250cm^3 volumetric flask using a funnel. finally, rinse equipment used with distilled water and add it to the flask, and top it up until the bottom of the meniscus touches the line. stopper the flask and invert it multiple times to make sure its mixed well.
How do you carry out a titration?
-rinse all equipment with water, then rinse the pipette with NaOH
-use a pipette and pipette filler to measure out 25^3 of NaOH, then place it in a conical flask with 3 drops of indicator (phenolphthalein)
-rinse the burette with acid and fill it up with acid until just above the 0cm^3 line
-let out enough acid until the bottom of the meniscus is touching the 0cm^3 line with no bubbles in the burette jet
-place the conical flask underneath the burette and let out around 20cm^3 of acid while swirling, and then add it dropwise when the colour starts to change from colourless to pink
-record the volume of acid used, then empty and wash the conical flask with water.
-refill the pipette with NaOH again and the acid in the burette.
-repeat steps x-x until you have at least 2 concordant results
How do you carry out a titration?
-rinse all equipment with water, then rinse the pipette with NaOH
-use a pipette and pipette filler to measure out 25^3 of NaOH, then place it in a conical flask with 3 drops of indicator (phenolphthalein)
-rinse the burette with acid and fill it up with acid until just above the 0cm^3 line
-let out enough acid until the bottom of the meniscus is touching the 0cm^3 line with no bubbles in the burette jet
-place the conical flask underneath the burette and let out around 20cm^3 of acid while swirling, and then add it dropwise when the colour starts to change from colourless to pink
-record the volume of acid used, then empty and wash the conical flask with water.
-refill the pipette with NaOH again and the acid in the burette.
-repeat steps x-x until you have at least 2 concordant results
if solution A is titrated against solution B, which solution goes where?
solution A is in the conical flask and solution B is the burette
What is usually in the conical flask?
the alkali
Why should you remove the funnel?
to stop the drops of acid dripping into the burette, which would result in an inaccurate, lower volume recorded as acid would replace air
Why does it not matter if the conical flasks contains drops of water?
the water does not change the moles of the acid/alkali
Why should you rinse the conical flask many times?
to ensure all the acid and alkali inside the flask all react during the titration
Why must you remove any bubbles from the burette jet?
the volume recorded would be greater as some of the acid would fill the volume of the air bubble and not go into the conical flask.
How do you calculate % apparatus uncertainty?
uncertainty/measurement x100
When would you times the % apparatus uncertainty calculation by 2?
after you’ve used the equipment more than once- for example when weighing solids (once for container, once for solid), or for % changes (like temperature change)
How do we reduce burette error?
-the smaller the burette’s volume, the larger the % error
-reduce the burette error by using a lower concentration of solution (diluting with water)
What calculations do you do afterwards to find the concentration of a substance?
for finding the alkali concentration-
acid moles (conc x vol), find mole ratio, do mol/vol for alkali
and vice versa
Why shouldn’t you use too much indicator?
it could lower the pH so would interfere with the results
