IRON TABLETS

Question 1

Why are iron tablets sometimes medically prescribed

Answer 1

To prevent anaemia [iron is needed for haemoglobin to carry oxygen]

Question 2

Why was some dilute sulfuric acid used in dissolving the tablets

Answer 2

So iron II does not oxidise to iron III with oxygen in air

Easier to dissolve

Question 3

Describe how exactly 250cm^3 of Fe2+ solution was prepared from five iron tablets

Answer 3

Find the mass of tablets
Crush tablets in mortar and pestle and transfer all the ground material to a beaker where it’s dissolved with dilute sulfuric acid
All of the solution including washings is transferred to a volumetric flask and the solution is made up until the bottom of the meniscus reaches the graduation mark with deionised water
The flask is stoppered and inverted several times

Question 4

Give the name and formula of the main active ingredient in iron tablets

Answer 4

Iron (II) sulfate, FeSO4

Question 5

Give two reasons why you use a number of iron tablets in this experiment

Answer 5

By using a number of tablets a solution of sufficiently high concentration is obtained so that the end point is within limits of the burette
Also, using 5 tablets rather than one tablet allows greater accuracy to be obtained as it lowers the percentage error

Question 6

Why is it necessary to grind up the iron tablets?

Answer 6

To help them dissolve more easily

Question 7

What items of laboratory equipment is used to grind up the iron tablets?

Answer 7

A mortar and pestle

Question 8

What are the two ways the iron ions can be oxidised

Answer 8

Oxygen in the air

Oxygen dissolved in the water

Question 9

Why is it important to rinse out the burette thoroughly with water at the conclusion of this experiment

Answer 9

Potassium permanganate stains glassware

Question 10

Why is it necessary to add dilute sulfuric acid to the conical flask

Answer 10

To supply H+ ions in order for the reduction of MnO4- to occur

Question 11

In this experiment, why is dilute sulfuric acid used rather than deionised water to dissolve the iron tablets?

Answer 11

If deionised water was used, the Fe2+ in the tablets would almost immediately oxidise to Fe3+. The sulfuric acid prevents the oxidation occuring.

Question 12

Why are burette readings taken from the top of the meniscus?

Answer 12

Dark colour of manganate solution makes the meniscus difficult to see

Question 13

Why is a rough titration carried out?

Answer 13

To determine the approximate end-point. This can then be used to get accurate results in the subsequent titrations.

Question 14

Why is more than one titration carried out subsequently

Answer 14

To reduce experimental error, by getting the mean of the accurate titres.

Question 15

Prior to the titration, what steps are taken to minimise error

Answer 15

All glassware is washed with deionised water. The burette and pipette respectively are rinsed with the solution they are to contain. The tap of the burette is opened briefly to fill the part of the burette below the tap.

Question 16

If a brown precipitate appears during the titration, what does this indicate and how can it be remedied?

Answer 16

Mn(IV) is formed, because of incomplete reduction of the Mn(VII). This should only happen if there is insufficient sulfuric acid in the conical flask. The remedy is to add more dilute sulfuric acid to the flask, or, preferably, to repeat the experiment with sufficient acid present in the flask.

Question 17

Describe the correct procedure for rinsing the burette before filling it with the solution it is to deliver

Answer 17

Rinse with deionised water and then rise with solution it is to contain

Question 18

Which solution is in the burette and the pipette

Answer 18

Burette - Pottasium Permanganate

Pipette - Iron solution

Question 19

Why is it important to fill the part below the tap of the burette?

Answer 19

Air will be displaced by the solution which would give an inaccurate reading, affecting the result of the experiment.

Question 20

Describe clearly the procedure for using a pipette to measure exactly 25cm^3 portions of the iron solution into the titration flask
(to make up solution in conical flask)

Answer 20

Rinse with deionised water followed by iron solution
Fill pipette using a pipette filler to above the graduation mark
Adjust to have bottom of the meniscus on mark and read at eye level
Drain under gravity into titration flask, touch tip of pipette against the side of the flask to add droplet adhering to outside tip
(add diluted sulfuric acid to acidify solution)

Question 21

In using a burette, why is it important to clamp it vertically

Answer 21

To ensure the mensicus is horizontal and level with the graduations on the burette. This is necessary for accurate readings of the burette

Question 22

How would you know that the Mn2+ ions have been formed

Answer 22

When the solution is colourless

Question 23

What is the solution titrated against?

Answer 23

Previously standardised potassium manganate (VII)