Titrations - Acids and Bases

Question 1

What is a titration?

Answer 1

It is a laboratory procedure where a measured volume of one solution is added to a known volume of another solution until the reaction is complete

Question 2

What is a primary standard?

Answer 2

It’s a water soluble substance that is stand and available in pure form. It can be used to make a solution of known concentration

Question 3

What is a molar solution?

Answer 3

It’s a solution that contains 1 mole of a solute dissolved in 1 litre of solution

Question 4

What is a standard solution?

Answer 4

It’s a solution whose concentration is accurately known

Question 5

How to prepare a primary standard -

Why is a volumetric flask used?

Answer 5

When it is filled to the calibration mark at the temperature stated on the flask, it contains a specific known volume therefore is more accurate

Question 6

How to prepare a primary standard -

What primary standard is used?

Answer 6

Anhydrous sodium carbonate

Question 7

How to prepare a primary standard -

What is used to measure mass of solute and ensure it’s accurate?

Answer 7

Analytical balance

Question 8

How to prepare a primary standard -

What is the purpose of the wash bottle?

Answer 8

Ensure no solution is lost when transferring

Question 9

How to prepare a primary standard -

How do you ensure solution is homogenous?

Answer 9

Stopper flask and invert it several times

Question 10

How to prepare a primary standard -

Purpose of narrow neck of volumetric flask?

Answer 10

It is necessary to read meniscus

Question 11

Describe the procedure to prepare a primary standard solution of sodium carbonate

Answer 11

• weigh the solute accurately using analytical balance
• transfer sodium carbonate to deionised water [wash bottle]
• stirring rod to mix and dissolve all of sodium carbonate in water
• using funnel, pour into volumetric flask [filled to calibration mark, specific known volume]
• rinse beaker and add rinsings to flask
• carefully being bottom of mensicus up to graduation mark on volumetric flask
• stopper flask and invert several times to ensure homogenous solution

Question 12

How to prepare a primary standard -

Why is anhydrous sodium carbonate used?

Answer 12

Available in pure form
Stable
Water soluble

Question 13

What is a homogenous solution?

Answer 13

An evenly mixed solution

Question 14

What’s the objective of standardisation?

Answer 14

To find it’s concentration accurately

Question 15

Why can’t standard solutions be made directly?

Answer 15

They are not readily available in pure form

Question 16

Standardisation of a hydrochloric acid solution using a standard solution of sodium carbonate -
What indicator solution is used and what’s the colour change?

Answer 16

Methyl orange indicator solution

Yellow - peach/pink

Question 17

Precautions to ensure accurate titration results

Answer 17

• burette is washed out with pure water and then solution it is to contain
• solution added using beaker and funnel
• tap of burette is opened briefly to fill the part of the burette below the tap [displaces air]
• burette filled up until the label of the liquid is above the 0cm3 mark
• tap is opened of burette to ensure its at definite mark
• burette readings taken at eye level : bottom of meniscus read
• pipettes washed with pure water and then solution to be contained [conical with only water]
• indicator either weak acids or weak bases adding too much with affect accuracy
• white tile
• conical flask swirled and any solution on sides can be washed down using water bottle
• rough titrations
• mean of titres is result

Question 18

Why is a burette more accurate than a graduated cylinder

Answer 18

Markings are easier to read

Question 19

Burette -

Why is the funnel removed before adjusting the burette to zero?

Answer 19

Ensure no drops fall into the burette which would give an inaccurate reading

Question 20

Burette -

Why must the burette be vertical?

Answer 20

Allow the meniscus to be properly lined up with graduation mark

Question 21

Burette -

Why is it rinsed first with deionised water and then solution to contain?

Answer 21

Deionised water - remove impurities

Solution to contain - removes remaining drops of water which may dilute solution

Question 22

Burette -

Why is the tap opened?

Answer 22

The tip must be full too as the graduation on the burette includes this space and therefore rid of air bubbles present - which would yield false results

Question 23

Safety precautions when filling burette

Answer 23

• Remove funnel before adjusting to zero so no drops fall into burette
• Vertical to ensure the mensicus is properly in line with graduation mark
• rinse first with deionised water [remove impurities] solution to contain [remove remaining drops of water which may dilute solution]
• read meniscus at eye level
• tip must be full as the graduation on burette includes this space

Question 24

What precautions should be taken when filling the pipette?

Answer 24

• always use pipette filler
• rinse with deionised water [remove impurities] and solution it is to contain [removes remaining drops of water which may dilute solution]
• read mensicus at eye level

Question 25

Wat precautions should be taken when delivering from pipette?

Answer 25

Hold pipette vertically | Touch tip of pipette against inside of conical flask to release last drop.

Question 26

Why is the conical flask used in these experiments?

Answer 26

Shaped to prevent spillage when being swirled

Question 27

Why is conical flask only rinsed with deionised water?

Answer 27

It should not be rinsed with solution it is to contain because the remaining drops will mean he total volume in the flask will be unknown

Question 28

During the titration, why are the sides of the flask washed down?

Answer 28

Ensure all the liquid from burette reacts in conical flask

Question 29

Give one reason why a volumetric flask is preferable to a graduated cylinder

Answer 29

It’s a more accurate piece of equipment - Narrow neck on flask and also when it is filled to the calibration mark, with temperature shown, there is a specific known volume

Question 30

Give one reason why a conical flask is preferable to a beaker

Answer 30

It’s easier to mix solutions due to shape - wide base, avoids spillages

Question 31

During the titrations, drops of the hydrochloric acid were noticed on the sides of the conical flask. What action would you take to deal with this problem? Why is it possible to take this action without affecting the result of the titration?

Answer 31

Wash down with deionised/distilled water Water does not affect the amounts of either reactant because they were both measured before they entered the flask by the pipette and burette

Question 32

In volumetric analysis, what is the advantage in carrying out a rough titration?

Answer 32

It gives an indication of the required volumes of both reagents needed for neutralisation, further titrations can be carried out much more quickly when the expected point is known

Question 33

Hydrochloric acid/sodium hydroxide titration and the use of this titration in making the salt sodium chloride - What is the purpose of the HCL

Answer 33

HCL has been standardised - know concentration. it is used to find concentration of sodium hydroxide

Question 34

Hydrochloric acid/sodium hydroxide titration and the use of this titration in making the salt sodium chloride - To obtain a sample of salt

Answer 34

- place 25cm3 of the sodium hydroxide solution in a beaker with no indicator - using results from earlier, add enough hydrochloric acid to neutralise it - gently hear solution until all water has been evaporated. Sample of sodium chloride will remain

Question 35

Determining the concentration of ethanoic acid in vinegar - | What indicator is used and what is the colour change?

Answer 35

Phenolphthalein indicator | Pink to colourless

Question 36

Determining the concentration of ethanoic acid in vinegar - | Why is the vinegar diluted?

Answer 36

To avoid as very small titre which would reduce the accuracy of the experiment

Question 37

Determining the concentration of ethanoic acid in vinegar - | How would you dilute the vinegar?

Answer 37

- place 25cm2 of vinegar in a 250cm2 volumetric flask and dilute with water up until calibration mark - stopper and invert several times - homogenous solution

Question 38

Procedure of a titration

Answer 38

- rinse burette, puppets and conical flask - fill pipette - base and add to conical flask - add indicator to conical flask - fill burette with acid to the 0cm3 mark, open tap - rough titration, three accurate titrations - calculate

Question 39

How do you calculate the concentration of ethanoic acid in diluted vinegar solution?

Answer 39

- formula - multiply by 10 - find grams - divide by 10

Question 40

Determination of the amount of water of crystallisation in hydrated sodium carbonate - What indicator is used and what is the colour change?

Answer 40

Methyl orange | Yellow to peach/pink

Question 41

Determination of the amount of water of crystallisation in hydrated sodium carbonate - How do you make up sodium carbonate solution?

Answer 41

SAME AS PRIMARY STANDARD - weight solute of hydrated sodium carbonate accurately - add to beaker of deionised water and wash down - transfer with funnel into volumetric flask ad add water to the graduation mark - stopper and invert

Question 42

How do you determine the formula of hydrated sodium carbonate?

Answer 42

GRAMS PER LITRE