CHEM PRACTICAL Flashcards
(24 cards)
Why is HCL and HNO3 not used to acidify KMno4
This is because HCl is a RA while HNO3 is also a OA
Why is starch indicator added to iodine thiosulfate solution?
This is to provide a sharper change of colour from dark blue to colourless instead of yellow to colourless
Why is starch not added at the beginning of the titration?
Starch is not added at the beginning because iodine molecules can get stuck in the long spiral starch molecules when the concentration of iodine is high
Titration readings to how many dp?
2 dp
How to improve on the readings for KMnO4?
Read the top of the miniscus instead as KMnO4 is dark purple
What to include in table to Gravimetric analysis via heating
Mass of test tube and FA1
Mass of empty test tube
Mass of FA1 used
For constant heating
same as the top plus
mass of empty weighing bottle
mass of FA… used
initial temp
final temp
change in temp
Temperature to how many dp
1
mass to how many dp
3
Why must tube be heated gently
This is because strong heating will cause the tube to undergo sudden thermal expansion which causes it to crack
Why are test tubes cooled before they are weighed?
Test tubes are cooled first because objects at high temperatures have fluctuating mass readings due to air convection
Why must we heat to constant mass?
To ensure complete decomposition
For QA, which of the ions doesn’t react with excess NaOH and which is the anomaly
Cu dosent and the anomaly is Al which has a complex ion charge of -1
Which ion does not produce complex ion when reacting with excess ammonia
Al and chromium the rest produce complex ions with the same charge as them
What is the technique to describe the reaction observed for complex ions
list out the two eqns on for ppt and one in excess use LCP to determine the steps
For small highly charged cations like Al3+, Cr3+ and Fe3+, why are they acidic in water
In aq solution, they exists as aqua complex ions, like (Al(OH)6) 3+ . Due to its high charge and small size, Al3+ has a high charge density thus, is strongly polarising, The electron density in the O-H bonds are drawn towards the Al3+ ions enabling the H2O molecules bonded to it to be proton donors while the free H2O act as a base.
What is the appropriate range of volume for acid in a burette
10-25 such that its not too low to the point percentage apparatus error is high and not too high for unnecessary waste.
What indicators which types of reactions
SB WA use thymol blue
SA WB use methyl orange
What are some sources of errors for titration
indicators are WA/WB so excessive amt changes PH
How to calculate weighted average temperature
V1/(V1+V2) x T1 …
Why put the Styrofoam cup in the beaker
- to prevent it from toppling over
2.the air trapped between the two acts as an insulator to minimise the heat lost to the environment
Why certain temperatures cannot be measured>
This is because the reaction is still occurring at a rapid rate cause temperature to fluctuate a alot
How to improve on inaccurate temperature
Use a data logger attached to a temperature probe
Why is a dry beaker used?
To ensure the total volume of the solution remains constant
Why is total volume kept constant
This is to ensure that FA1 mixture concentration is proportional to FA1 volume
