Titration

Question 1

Standard solution

Answer 1

A solution which concentration is accurately known
Ie the solution in the conical flask

Question 2

What can standard solutions be used for?

Answer 2

Finding the concentrations of unknown solutions by finding out the volume of the standard solution needed to neutralise it

Question 3

What makes up a standard solution?

Answer 3

A primary standard + making it up with an accurate volume of distilled water

Question 4

Primary standard

Answer 4

Substances that are dissolved in distilled water to produce a primary standard
By weighing

Question 5

What should a primary standard ideally be?

Answer 5

Solids with high molar masses
Available in high purity
Chemically stable so won’t decompose in air
Won’t absorb any water from atmosphere
Soluble in water
React rapidly with titre solution

Question 6

Why is HCl not used as a primary standard

Answer 6

Does not exist in solid form only as a gas or aqueous solution

Question 7

Why is NaOH not used as a primary standard

Answer 7

Reacts rapidly with air to form CO2 and H2O
So when measuring, not measured accurately because traces of these compounds

Question 8

Step 1 of making a standard solution

Answer 8

Add between 2.3 and 2.5 g of sulfamic acid to the weighing bottle and weigh accurately on a balance

Question 9

Step 2 of making a standard solution

Answer 9

Transfer as much as possible of the acid to a clean beaker and reweigh the weighing bottle
Wash out weighing bottle with water to ensure all powder is transferred

Question 10

Step 3 of making a standard solution

Answer 10

Add about 50 cm3 of distilled water to the beaker and stir until all of the sulfamic acid has dissolved

Question 11

Step 4 of making a standard solution

Answer 11

Pour solution from beaker into volumetric flask

Question 12

Step 5 of making a standard solution

Answer 12

Rinse sides of beaker with distilled water and pour the washings into the flask to ensure all solution is transferred repeat 3x
Don’t worry about water volume at this point because it is no where near required volume

Question 13

Step 6 of making a standard solution

Answer 13

Rinse filter funnel used for transferring solution from beaker to volumetric flask

Question 14

Step 7 of making a standard solution

Answer 14

Fill up the volumetric flask to the graduated mark with deionised water, adding drop by drop to ensure meniscus sits on line

Question 15

Step 8 of making standard solution

Answer 15

Stopper flask and invert multiple times to ensure a thorough mixture and that there is a uniform solution = all of it is sulfamic acid

Question 16

What happens if you overshoot graduated mark in a standard solution?

Answer 16

Restart

Question 17

How do we find the mass of primary standard added?

Answer 17

Find mass of weighing bottle AND sulfamic acid
Reweigh weighing bottle after adding sulfamic added and any traces left
Take away first value from other = true value of sulfamic acid added

Question 18

Why do we weigh by difference?

Answer 18

So we can find the true value of the primary standard added by taking in to account any traces remaining on weighing bottle

Question 19

How do we find the concentration of the primary solution in the volumetric flask?

Answer 19

Calculate number of moles with moles = mass weighed out divided by Mr
Conc = moles just calculated divided by volume in the flask

Question 20

Titration use

Answer 20

A method of working out the volumes of two solutions that react together, and using the results to calculate the concentration of one of the solutions
Where one of the concentrations is known

Question 21

Outline of titration

Answer 21

Add the burette solution to the conical flask til the equivalence point of the titration and the end point of the indicator is reached
Record the lowest part of the meniscus + record the titre
Repeat the titration until concordant titres are obtained

Question 22

Which solution goes in the burette?

Answer 22

The standard solution with the concentration accurately known ie sulfamic acid concentration

Question 23

Which solution goes in the conical flask?

Answer 23

The solution with an unknown concentration

Question 24

Step 1 of titration

Answer 24

Rinse the conical flask with deionised water and place it on a white tile.

Question 25

Why rinse the conical flask with deionised water rather than the solution we are going to add?

Answer 25

Because then if we rinsed out with the solution, then any traces left will increase its concentration thus increase titre over true value
And using water won’t mess up results because same moles of that solution still in beaker so the titre volume is same

Question 26

Why use a white tile?

Answer 26

Provides a constant white background to observe colour change clearly

Question 27

Step 2 of titration

Answer 27

Rinse glass pipette with deionised water then the unknown solution

Question 28

Why do we rinse the pipette with both deionised water and unknown solution?

Answer 28

We can rinse the pipette with unknown solution unlike conical flask because the contents of it will be added to the flask, being measured first so will not cause contamination

Question 29

Step 3 of titration

Answer 29

Use pipette and pipette filler to transfer 25cm3 of unknown solution into the conical flask
Ensure meniscus sits on graduated mark, repeat if not

Question 30

Step 4 of titration

Answer 30

Add 3 drops of indicator: methyl orange or phenolphthalein

Question 31

Methyl orange colour change

Answer 31

In acid = red
In alkali = pink

Question 32

Phenolphthalein colour change

Answer 32

In acid = colourless
In alkali = pink

Question 33

When should phenolphthalein be used?

Answer 33

With a strong acid and weak base
With a strong acid and a strong base

Question 34

When should methyl orange be used?

Answer 34

Weak acid and strong base
Strong acid and string base

Question 35

Step 5 of titration

Answer 35

Rinse burette with distilled water then rinse with some of the standard solution prepared

Question 36

Why rinse the burette with the standard solution?

Answer 36

Because it will remove any of the distilled water remaining in it which will dilute the standard solution and therefore means a higher titre required

Question 37

Step 6 of titration

Answer 37

Fill the burette with the sulfamic acid solution and set it up in the stand above the conical flask
Make sure bit between tap and tip is full

Question 38

Why fill up the but between tap and tip in the burette is full?

Answer 38

Because if not, then as solution is added it will fall and fill this point and won’t enter the conical flask

Question 39

Why is burette fitted so it’s tip is in conical flask’s neck?

Answer 39

To reduce risk of solution in burette ending up outside the conical flask

Question 40

Step 7 of titration

Answer 40

Record initial burette reading

Question 41

How to take readings from a burette and why?

Answer 41

To the precision of burette eg 0.05
And take from light background to ensure accuracy of reading from meniscus

Question 42

Step 8 of titration

Answer 42

Add burette solution to conical flask whilst swirling until colour change is seen then add drop by drop

Question 43

Step 9

Answer 43

Once permanent and slight colour change is seen, take the burette reading of the solution added then calculate tire of initial reading - final reading

Question 44

Why swirl and add drop by drop to solution?

Answer 44

To reduce risk of overshooting endpoint by adding drop by drop
And to continuously mix solution by swirling