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Flashcards in IRON TABLETS Deck (23):
1

Why are iron tablets sometimes medically prescribed

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

2

Why was some dilute sulfuric acid used in dissolving the tablets

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

3

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

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

4

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

Iron (II) sulfate, FeSO4

5

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

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

6

Why is it necessary to grind up the iron tablets?

To help them dissolve more easily

7

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

A mortar and pestle

8

What are the two ways the iron ions can be oxidised

Oxygen in the air
Oxygen dissolved in the water

9

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

Potassium permanganate stains glassware

10

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

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

11

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

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

12

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

Dark colour of manganate solution makes the meniscus difficult to see

13

Why is a rough titration carried out?

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

14

Why is more than one titration carried out subsequently

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

15

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

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.

16

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

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.

17

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

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

18

Which solution is in the burette and the pipette

Burette - Pottasium Permanganate
Pipette - Iron solution

19

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

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

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)

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)

21

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

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

22

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

When the solution is colourless

23

What is the solution titrated against?

Previously standardised potassium manganate (VII)