Volumetric Analysis

Question 1

What does the moles of solute after dilution equal?

Answer 1

The moles of solute before dilution

Question 2

What do you change and not change when you add water and dilute the solution?

Answer 2

• change concentration

- do not change the moles of solute

Question 3

What can colour intensity be measured by?

Answer 3

Using a colorimeter

Question 4

What does the colour intensity dependent on?

Answer 4

The concentration of the solution

Question 5

Define standard solution

Answer 5

A standard solution of know concentration

Question 6

Define primary standard

Answer 6

A primary standard is a substance (solute) that can be made up to a standard solution directly as it is available in 100% purity, is stable in air, has a high molar mass of accuracy in weighing and dissolves easily in water.

Question 7

Is a titration always needed to find a concentration?

Answer 7

No

Question 8

What are the only two examples of primary standards that are used in the syllabus?

Answer 8

• Anhydrous Na2CO3 (base), ammonium iron

- Sulphate (reducing agent)

Question 9

Define secondary standard

Answer 9

A secondary standard is a substance(solutes) that cannot be made up to a standard solution directly as it is not available in 100% purity, or is not stable in air, or has a low molecular mass and does not dissolve readily in water

Question 10

Define standardise

Answer 10

To standardise is to find out the concentration of a solution by titration or colorimetry

Question 11

What is the first step in preparing a solution?

Answer 11

Solute (if solid is weighed accurately on a clock glass using an electronic balance.

Question 12

What happens after the solute is weighed accurately on a clock glass?

Answer 12

All of the solute is transferred to a volumetric flask and made up to an accurately known volume e.g 250cm3

Question 13

Why is the solute made up to an accurately known volume?

Answer 13

• so the concentration can be calculated

- so there is enough solution to carry out 3 titrations

Question 14

What happens first to the solute if it is solid?

Answer 14

Tipped into a beaker

Question 15

What is the clock glass washed with?

Answer 15

Deionised water from a wash-bottle

Question 16

What happens after the clock glass is washed with deionised water?

Answer 16

The rinsings are added to the beaker and stirred with a clean dry glass rod until it dissolves

Question 17

What happens after the rinsings are added to the beaker?

Answer 17

The solution is poured into the volumetric flask with the aid of a funnel to prevent spillage

Question 18

What happens after the solution is added to the volumetric flask?

Answer 18

The funnel is removed and deionised water is added to the flask until the level of the solution is 1cm3 below the mark on the neck of the flask

Question 19

When do you stop adding the deionised water drop by drop to the volumetric flask?

Answer 19

Until the bottom of the meniscus is on the graduation mark and read at eye-level

Question 20

What does the solution in the flask have after the deionised water is added?

Answer 20

A concentratinon gradient

Question 21

What is done near the end to make the solution homogenous?

Answer 21

The flask is stoppered, inverted 20-30 times and shaken to make the solution homogenous

Question 22

Why does the volumetric flask have a narrow neck?

Answer 22

To make the measurement accurate and able to see the bottom of the meniscus clearly.

Question 23

What is used to measure out an exact volume if the solute is in liquid form (bleach or vinegar)?

Answer 23

A properly rinsed pipette

Question 24

How is the solute transferred to the volumetric flask if its in liquid form?

Answer 24

By touching the tip of the inside of the volumetric flask

Question 25

What is the apparatus needed to prepare a standard solution of sodium carbonate? (not a titration)

Answer 25

- Safety glasses - 250cm3 - Volumetric flask - Beaker - Funnel - Glass rod - Dropper - Electronic balance - Wash bottle

Question 26

Materials needed to prepare a standard solution of sodium carbonate? (not a titration)

Answer 26

- 2.65g of sodium carbonate | - Deionised water

Question 27

volumetric analysis

Answer 27

reacting 2 solutions together to find the concentration of one of them

Question 28

to find the concentration what information do you need to have

Answer 28

amount of solute | amount of solution

Question 29

pwv or %w/v

Answer 29

percentage weight per volume | grams per 100 cm cubed

Question 30

pww or %w/w

Answer 30

grams per 100 cm cubed

Question 31

pvv or %v/v

Answer 31

cm cubed per cm cubed

Question 32

ppm

Answer 32

parts per million | milligrams per litre

Question 33

M

Answer 33

molarity | moles per litre

Question 34

why is the pipette used for solutions at room temperature only?

Answer 34

liquids expand on heating and contract on cooling

Question 35

how do you clean the pipette?

Answer 35

first with deionised water and then the solution that it will contain

Question 36

what do you use to fill the pipette

Answer 36

a pipette filler

Question 37

why do you use a pipette filler

Answer 37

as solutions may be poisonois

Question 38

how do you fill the pipette?

Answer 38

draw the solution above the graduation mark and run out until the bottom of the meniscus reaches the zero mark, read at eye level

Question 39

how is the solution transferred from a pipette? why?

Answer 39

by touching the tip off the inside of the flask, this ensures the exact volume is transferred

Question 40

do you blow the last drop out of the pipette? why?

Answer 40

no, it is accounted for in the calibration of the pipette

Question 41

what is the function of the narrow neck on the conical flask?

Answer 41

prevents spillage during swirling

Question 42

what is the function of the conical flask in a titration?

Answer 42

this is the vessel in which the two solutions will react

Question 43

what do you wash the conical flask with and why?

Answer 43

only deionised water as not to change the number of moles of solute taking part in the reaction

Question 44

how accurate does the burette measure?

Answer 44

to 0.1 cm cubed accuracy

Question 45

how is the burette clamped and why?

Answer 45

clamped vertically to avoid the error of parallax

Question 46

where does the acid USUALLY go?

Answer 46

the burette

Question 47

where does the base USUALLY go?

Answer 47

the pipette

Question 48

what do you wash the burette with before the titration and why?

Answer 48

deionised water and then the solution it will contain. water droplets would dilute the solution

Question 49

how do you fill the burette

Answer 49

close tap, add a funnel, fill above zero graduation mark, remove funnel, add a waste beaker underneath. read at eye level, open tap until the bottom of the meniscus reaches the zero graduation mark.

Question 50

one liquid that is read from the top of the meniscus in the burette and why

Answer 50

KMnO4 because of its deep purple colour