module 2 - acid-base titrations

Question 1

what’s a titration?

Answer 1

a technique used to accurately measure the volume of one solution that reacts exactly with another solution

Question 2

what are 3 things can titrations be used for?

Answer 2

• finding concentration of a solution
• identification of unknown chemicals
• finding the purity of a substance

Question 3

what’s a standard solution?

Answer 3

a solution of known concentration

Question 4

what is used to make a standard solution?

Answer 4

a volumetric flask

Question 5

what is a volumetric flask used for in titrations?

Answer 5

to make up a standard solution very accurately

Question 6

why is using a volumetric flask good?

Answer 6

because they can measure volumes very precisely

Question 7

what are the 1st 3 steps in preparing a standard solution?

Answer 7

• weigh solid accurately
• dissolve solid in a beaker using distilled water (less than what will be needed to fill the vol flask to the mark)
• transfer this solution to vol flask. (last traces of solution are rinsed into the vol flask with distilled water)

Question 8

what next step is taken after rinsing and solution are first put into the volumetric flask?

Answer 8

• flask is filled to the graduation line by adding distilled water one drop at a time until the bottom of the meniscus lines up exactly with the mark

Question 9

why is it important to be careful when filling up the volumetric flask completely?

Answer 9

• if too much water is added, the solution = too dilute and must be made again

Question 10

how should you view the graduation mark and meniscus and why?

Answer 10

• at eye-level

- for accuracy

Question 11

what’s the final step after the volumetric flask is completely filled?

Answer 11

• its slowly inverted several times, to mix the solution thoroughly and evenly

Question 12

what happens if you dont invert the mixture?

Answer 12

• titration results are unlikely to be consistent

Question 13

how can you see the solution mixing when yo invert the vol flask?

Answer 13

the more dense original solution moves through the solution

Question 14

what is the effect on the titre with the error of filling the flask with water above the grad line?

Answer 14

the titre would be less as solution is more dilute

Question 15

what is the effect on the titre when in error, the flask is not inverted?

Answer 15

• the solution used in the first titration would be more dilute than the solution used after.
• The first titre would need less solution

Question 16

in an acid-base titration what is titrated against what?

Answer 16

a solution of an acid is titrated against a solution of a base using a pipette and a burette

Question 17

how is a burette reading recorded?

Answer 17

to the nearest half division

Question 18

what is each burette reading measured to? what does this mean?

Answer 18

to the nearest +/- 0.05cm^3

• the reading always has 2 dp
• last decimal place is always 0/5

Question 19

what should you do when filling a burette to remove air bubbles?

Answer 19

run excess solution out through the tap

Question 20

where would you put the acid and alkali in a titration to find the concentration of hydrogen ions in an acid solution

Answer 20

• put acid in burette

- put alkali in conical flask

Question 21

what are the 1st 3 steps in doing an acid-base titration (before turning tap on)??

Answer 21

• add a measured volume of 1 solution (usually unknown one) to a conical flask using a pipette
• add the other solution (usually the standard solution) to the burette, and record the initial burette reading to nearest 0.05cm^3
• add a few drops of indicator to the conical flask solution!!

Question 22

for a titration, what is the step after the indicator is put in?

Answer 22

• run burette solution into conical flask, swirling the con. flask throughout it to mix both.
• soon, the indicator changes colour at the end point of the titration

Question 23

what does the end point do?

Answer 23

it’s used to indicate the volume of 1 solution that exactly reacts with the volume of the 2nd solution.

Question 24

after the end point is reached in a titration what is the next step?

Answer 24

• record the final burette reading

Question 25

what is the titre? How is it found?

Answer 25

• The volume of solution added from the burette

- By subtracting the initial from the final burette reading! (F-I)

Question 26

when doing titrations, what is always done first? why?

Answer 26

• a quick trial titration

- to find the approximate titre

Question 27

how many times are titrations accurately repeated?

Answer 27

until 2 accurate titres are concordant (they’re within 0.10cm^3 of each other)
{e.g. between 24.60, 24.30 and 24.80, if concordant criteria was 0.20, then only 1 and 3 are concordant. 2 is irrelevant}

Question 28

in titrations, how should the burette solution be put in towards the endpoint?

Answer 28

dropwise until endpoint reached

Question 29

what is the tire also known as?

Answer 29

the volume of the solution that’s been added

Question 30

which titration result is ignored in calculations?

Answer 30

the rough titre

Question 31

when calculating mean titre, what do you include and what dont you?

Answer 31

• include the titres that are concordant

- don’t include any that are too low or too high

Question 32

what should u have in your titration results table?

Answer 32

• final burette reading in cm^3
• initial burette reading in cm^3
• titre in cm^3
• mean titre in same units
• boxes for trial and for 3 repeats

Question 33

explain the effect of the error of the pipette having an air bubble inside?!

Answer 33

tire would be less as less solution has been added than the correct pipette volume

Question 34

explain the effect of the error of the burette readings being taken from the top of the meniscus?

Answer 34

no effect as volume is measured by difference between two readings.

Question 35

explain the effect of the error of the burette having an air bubble inside?!

Answer 35

if a bubble is left in the neck of the burette, the air could be released during the titration leading to an error in the titre

Question 36

when working out mean titre, what is it important to use?

Answer 36

• only the closest accurate titres

Question 37

what would happen if you included all the titres in the mean?

Answer 37

you lose the accuracy of the titration technique

Question 38

what 2 things will you know from the results of a titration?

Answer 38

• the concentration and reacting volume of one of the solutions
• just the reacting volume of the other solution

Question 39

what is the pattern (3 steps) used to find out info about the unknown compound?

Answer 39

1) work out the amount in mol of the solute in the solution (the one that u know the conc and vol for)
2) use equation to find amount in mol of the solute in the other solution
3) work out the unknown info about the solute in the other solution

Question 40

X

Answer 40

X