Pc2 Practical Knowledge Flashcards
(25 cards)
Describe how to make a standard solution
Dissolved solid in distilled water
Transfer solution into volumetric flask using a funnel
Use distilled water to wash the contents of the beaker and stirring rod and funnel into volumetric flash to make up 250cm mark
Invert the volumetric flask 3 or more times
Why do you wash the tools used with distilled water
To make sure all the moles is in the standard solution
Why do we rinse the pipette with the alkali
So that water does not dilute the barium hydroxide
Why do we remove the funnel from the burette before titration
Drops of acid could fall into the burette
Why should we make sure the tap is filled and there are no air bubble
Could cause use to record an inaccurate titre
Why do we continually swirl the conical flask
To make sure the acid and base are evenly mixed
So we accurately spot when neutralisation occurs
What must we continually do to conical flash
Rinse with water
Why do we rinse the concial flash during the titration
Ensures all the moles of the solution are in the solution
Why do we repeat the titration till we have two concordant results
Increase the reliability of the titre
Concordant titres are
Within 0.1cm³ of each other
Why is conical flask used instead of a titration
Prevents acid from splashing out
Makes sure all the moles of acid are in acid by adding water
Easy to swirl without spilling
Why should we only add a few drops of indicator
It would affect titration results
Would require more base to neutralise as the indicator is a weak acid
Can adding the water to a conical flash affect the titration
No it will not
Water doesn’t react with acid
The number of moles will remain the same
What would happen id the weigh boat is not rinsed
Concentration would decrease
Not enough solute transferred
What could would happen if meniscus was just above the line of flask
Concentration would decrease
More volume of water more diluted
What would happen if the solution was not inverted at the end
Conc would decrease
Not consistent
What would happen if the soild became hydrated before it weighed out
Conc would decrease
Mass of water is included
What would happen if there were droplets of water on the side of the flask above the line before it was inverted
Conc would decrease
What could happen if the solid was not completely dissolved before it was added to the flask
Conc would decrease
No of moles decrease if not fully dissolved
Titration practical
Pipette 25cm of the hydrochloric acid into the conical flash
Add the phenolphthalein indicators 2 drops
Fill burette with sodium hydroxide
Make sure air bubbles are emover
Take initial burette reading then add naoh to acid
How to increase reduce uncertainty
Use a larger mass/ larger volume of titre
Use apparatus with higher resolution
Why is phenolpthalein a better indicator than universal indicators for titrations
What is a standard solution and what is an alkali
Solution of known concentration
Substance that releases OH- in solution
Suggest improvements to the practical of titration
Record mass accurately to 2 dp
Weigh by difference
Wash the soild from the weighing container into beaker
Invert concula flash several times to ensure solute is uniformly mixed
