Practical 2 - Preparation of a soluble salt by titration

Question 1

What are we trying to achieve with this practical?

Answer 1

Preparing crystals of sodium chloride by using titration followed by evaporation

Question 2

What type of crystals are we attempting to form via titration and evaporation here?

Answer 2

Sodium chloride

Question 3

What does sodium chloride form in this experiment?

Answer 3

Crystals

Question 4

The volume that could be held by the Burkett e

Answer 4

50cm^3

Question 5

The volume that could be held by the pipette

Answer 5

25cm^3

Question 6

The volume that cold be held by the conical flasks

Answer 6

100cm^3

Question 7

Apparatus

Answer 7

50cm^3 burette
Funnel
25cm^3 pipette + filler
100cm^3 conical flasks
Evaporating basin

Question 8

Molarities of the NaOH and HCl used

Answer 8

0.1moldm^3

Question 9

What were the chemicals used?

Answer 9

NaOH solution
HCl solution
Phenolphthalein indicator

Question 10

What type of indicator was used?

Answer 10

Phenolphthalein

Question 11

Phenolphthalein purpose in the practical

Answer 11

Indicator

Question 12

Risk of NaOH

Answer 12

Irritant

Question 13

Risk of HCl

Answer 13

Irritant

Question 14

Risk of phenolphthalein indicator

Answer 14

Flammable

Question 15

Which two solutions share the same risk here and what is it?

Answer 15

NaOH and HCl - both irritants

Question 16

What must we do before starting any titration and why?

Answer 16

Always rinse the burette and pipette with whatever we’re titrating with
(Water would increase the volume too much)

Question 17

What do we rinse the burette and pipette with?

Answer 17

Whatever we’re titrating with

Question 18

What do we rinse before beginning the titration?

Answer 18

The burette and pipette (with whatever we’re titrating with)

Question 19

Why can’t we rinse the burette and pipette out with water?

Answer 19

It would increase the volume too much

Question 20

How do we measure the NaOH solution?

Answer 20

With a pipette and filler

Question 21

What’s the first step?

Answer 21

Using a pipette and filler, measure 25cm^3 of NaOH solution and pour it into the conical flask

Question 22

Where does the NaOH solution go? Why?

Answer 22

The conical flask - could damage the burette

Question 23

How much phenolphthalein do we add? What to?

Answer 23

2 drops to the NaOH solution in the conical flask

Question 24

Where do we place the HCl solution and how?

Answer 24

In the burette using a funnel

Question 25

Which chemical goes in the burette and which goes in the pipette then the conical flask?

Answer 25

Burette - HCl
Conical flak - NaOH

Question 26

Where do we start our initial reading on the burette of HCl?

Answer 26

Anywhere that isn’t zero

Question 27

What must we do before taking the initial burette reading of HCl in the burette and why?

Answer 27

Remove the funnel so that additional substance doesn’t drip in

Question 28

How do we actually combine the NaOH and HCl?

Answer 28

Open the tap and add the HCl from the burette into the conical flask a little at a time while swirling the conical flask

Question 29

How do we know if we’ve neutralised the NaOH?

Answer 29

The phenolphthalein turns from pink to colourless

Question 30

When do we start and stop adding the HCl solution one drop at a time?

Answer 30

When the phenolphthalein starts to turn from pink to colourless
Stop when one drop is sufficient to turn the solution colourless

Question 31

What colour does the phenolphthalein turn from and to when the NaOH has been neutralised?

Answer 31

From pink to colourless

Question 32

What does it actually mean that the NaOH has been neutralised?

Answer 32

There’s the same number of moles of NaOH and HCl reacting

Question 33

Why don’t we include the first titre in our final results?

Answer 33

It’s just a rough titre

Question 34

What do we need two measurements to be between in order to move onto the next stage?

Answer 34

Within 0.2cm^3 of each other

Question 35

What can we do once we’ve got two measurements within 0.2cm^3 of eachother?

Answer 35

Carry out the titration again using 25cm^3 of NaOH solution an exactly the same volume of HCl solutions and do not add indicator this time

Question 36

What do we do differently in terms of the titration once we’ve got 2 measurements within 0.2cm^3 of eachother?

Answer 36

Carry it out using exactly the same volume of HCl solution needed
Do not add the indicator

Question 37

Once we’ve titrated for the last time using the correct volume of HCl to react with the NaOH an no indicator, what do we do?

Answer 37

Gently heat the solution from the conical flask in an evaporating basin until its volume decreases by about half

Question 38

How long do we heat the solution in the conical flask for?

Answer 38

Until its volume decreases by about half

Question 39

Whats the final step of this practical?

Answer 39

Leave the evaporating basin to cool, allowing crystals to form

Question 40

What happens when we leave the evaporating basin to cool?

Answer 40

Crystals form

Question 41

How do we calculate the titre (cm^3)?

Answer 41

Final volume - initial volume

Question 42

What decimal place to we write all of our results to?

Answer 42

2 d.p.

Question 43

What must we ensure in terms of the burette before beginning the titration?

Answer 43

That there’s water in the jet

Question 44

What must we ensure in terms of the pipette before beginning the titration?

Answer 44

That all bubbles have been flushed out

Question 45

What do we do once crystals have formed?

Answer 45

Filter and dry them

Question 46

Why don’t we use a universal indicator instead of pthenolphthalein?

Answer 46

The end point of the universal indicator is too narrow