Volumetric Analysis Flashcards
What does the moles of solute after dilution equal?
The moles of solute before dilution
What do you change and not change when you add water and dilute the solution?
- change concentration
- do not change the moles of solute
What can colour intensity be measured by?
Using a colorimeter
What does the colour intensity dependent on?
The concentration of the solution
Define standard solution
A standard solution of know concentration
Define primary standard
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.
Is a titration always needed to find a concentration?
No
What are the only two examples of primary standards that are used in the syllabus?
- Anhydrous Na2CO3 (base), ammonium iron
- Sulphate (reducing agent)
Define secondary standard
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
Define standardise
To standardise is to find out the concentration of a solution by titration or colorimetry
What is the first step in preparing a solution?
Solute (if solid is weighed accurately on a clock glass using an electronic balance.
What happens after the solute is weighed accurately on a clock glass?
All of the solute is transferred to a volumetric flask and made up to an accurately known volume e.g 250cm3
Why is the solute made up to an accurately known volume?
- so the concentration can be calculated
- so there is enough solution to carry out 3 titrations
What happens first to the solute if it is solid?
Tipped into a beaker
What is the clock glass washed with?
Deionised water from a wash-bottle
What happens after the clock glass is washed with deionised water?
The rinsings are added to the beaker and stirred with a clean dry glass rod until it dissolves
What happens after the rinsings are added to the beaker?
The solution is poured into the volumetric flask with the aid of a funnel to prevent spillage
What happens after the solution is added to the volumetric flask?
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
When do you stop adding the deionised water drop by drop to the volumetric flask?
Until the bottom of the meniscus is on the graduation mark and read at eye-level
What does the solution in the flask have after the deionised water is added?
A concentratinon gradient
What is done near the end to make the solution homogenous?
The flask is stoppered, inverted 20-30 times and shaken to make the solution homogenous
Why does the volumetric flask have a narrow neck?
To make the measurement accurate and able to see the bottom of the meniscus clearly.
What is used to measure out an exact volume if the solute is in liquid form (bleach or vinegar)?
A properly rinsed pipette
How is the solute transferred to the volumetric flask if its in liquid form?
By touching the tip of the inside of the volumetric flask
What is the apparatus needed to prepare a standard solution of sodium carbonate? (not a titration)
- Safety glasses
- 250cm3
- Volumetric flask
- Beaker
- Funnel
- Glass rod
- Dropper
- Electronic balance
- Wash bottle
Materials needed to prepare a standard solution of sodium carbonate? (not a titration)
- 2.65g of sodium carbonate
- Deionised water
volumetric analysis
reacting 2 solutions together to find the concentration of one of them
to find the concentration what information do you need to have
amount of solute
amount of solution
pwv or %w/v
percentage weight per volume
grams per 100 cm cubed
pww or %w/w
grams per 100 cm cubed
pvv or %v/v
cm cubed per cm cubed
ppm
parts per million
milligrams per litre
M
molarity
moles per litre
why is the pipette used for solutions at room temperature only?
liquids expand on heating and contract on cooling
how do you clean the pipette?
first with deionised water and then the solution that it will contain
what do you use to fill the pipette
a pipette filler
why do you use a pipette filler
as solutions may be poisonois
how do you fill the pipette?
draw the solution above the graduation mark and run out until the bottom of the meniscus reaches the zero mark, read at eye level
how is the solution transferred from a pipette? why?
by touching the tip off the inside of the flask, this ensures the exact volume is transferred
do you blow the last drop out of the pipette? why?
no, it is accounted for in the calibration of the pipette
what is the function of the narrow neck on the conical flask?
prevents spillage during swirling
what is the function of the conical flask in a titration?
this is the vessel in which the two solutions will react
what do you wash the conical flask with and why?
only deionised water as not to change the number of moles of solute taking part in the reaction
how accurate does the burette measure?
to 0.1 cm cubed accuracy
how is the burette clamped and why?
clamped vertically to avoid the error of parallax
where does the acid USUALLY go?
the burette
where does the base USUALLY go?
the pipette
what do you wash the burette with before the titration and why?
deionised water and then the solution it will contain. water droplets would dilute the solution
how do you fill the burette
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.
one liquid that is read from the top of the meniscus in the burette and why
KMnO4 because of its deep purple colour
