CHEM PRACTICAL

Question 1

Why is HCL and HNO3 not used to acidify KMno4

Answer 1

This is because HCl is a RA while HNO3 is also a OA

Question 2

Why is starch indicator added to iodine thiosulfate solution?

Answer 2

This is to provide a sharper change of colour from dark blue to colourless instead of yellow to colourless

Question 3

Why is starch not added at the beginning of the titration?

Answer 3

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

Question 4

Titration readings to how many dp?

Answer 4

2 dp

Question 5

How to improve on the readings for KMnO4?

Answer 5

Read the top of the miniscus instead as KMnO4 is dark purple

Question 6

What to include in table to Gravimetric analysis via heating

Answer 6

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

Question 7

Temperature to how many dp

Answer 7

1

Question 8

mass to how many dp

Answer 8

3

Question 9

Why must tube be heated gently

Answer 9

This is because strong heating will cause the tube to undergo sudden thermal expansion which causes it to crack

Question 10

Why are test tubes cooled before they are weighed?

Answer 10

Test tubes are cooled first because objects at high temperatures have fluctuating mass readings due to air convection

Question 11

Why must we heat to constant mass?

Answer 11

To ensure complete decomposition

Question 12

For QA, which of the ions doesn’t react with excess NaOH and which is the anomaly

Answer 12

Cu dosent and the anomaly is Al which has a complex ion charge of -1

Question 13

Which ion does not produce complex ion when reacting with excess ammonia

Answer 13

Al and chromium the rest produce complex ions with the same charge as them

Question 14

What is the technique to describe the reaction observed for complex ions

Answer 14

list out the two eqns on for ppt and one in excess use LCP to determine the steps

Question 15

For small highly charged cations like Al3+, Cr3+ and Fe3+, why are they acidic in water

Answer 15

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.

Question 16

What is the appropriate range of volume for acid in a burette

Answer 16

10-25 such that its not too low to the point percentage apparatus error is high and not too high for unnecessary waste.

Question 17

What indicators which types of reactions

Answer 17

SB WA use thymol blue
SA WB use methyl orange

Question 18

What are some sources of errors for titration

Answer 18

indicators are WA/WB so excessive amt changes PH

Question 19

How to calculate weighted average temperature

Answer 19

V1/(V1+V2) x T1 …

Question 20

Why put the Styrofoam cup in the beaker

Answer 20

1. 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

Question 21

Why certain temperatures cannot be measured>

Answer 21

This is because the reaction is still occurring at a rapid rate cause temperature to fluctuate a alot

Question 22

How to improve on inaccurate temperature

Answer 22

Use a data logger attached to a temperature probe

Question 23

Why is a dry beaker used?

Answer 23

To ensure the total volume of the solution remains constant

Question 24

Why is total volume kept constant

Answer 24

This is to ensure that FA1 mixture concentration is proportional to FA1 volume