Researching Chemistry 1 - Stochiometry, Gravimetric and Volumetric Analysis Flashcards
What is a stochiometric equation, and what does it tell you?
A balanced chemical equation, and it tells you the mole ratios
A quantitative reaction is one that ___ ___ according to the ___ ___.
reacts completely, mole ratios
If you want to find the exact quantity of a substance present in a compound, you can carry out a ___ reaction, and use the ___ of the reaction to determine the mass.
quantitative, stochiometry
Some common units for concentration are: ___, ___ by ___, ___ by ___, and ___.
PPM, % by volume, % by mass, and mol/L
Two methods commonly used in quantitative analysis are ___ and ___ analysis.
Gravimetric, volumetric
What is gravimetric analysis?
A process used to determine the mass of an element or compound present in a substance, by changing that substance to one of known chemical composition
What is ‘weighing accurately approximately’?
Measuring out a rough mass of something, but knowing it’s mass to three d.p. (eg ‘measure 2.5g acc. approx.’ - and you then measure 2.476)
What does the tare function do on a scale?
Sets it to zero
Once the product has been __, it can be ___ and ___.
Isolated / collected, purified, weighed
What is heating to a constant mass?
A process of repeated heating and cooling cycles, until the substances mass remains constant.
>The heating drives off moisture and the cooling is done in a dessicator to prevent any moisture from being absorbed
Once the mass of the substance has been determined, the number of ___ can be calculated using the formula: ___.
moles, n = m/GFM
The formula of the compound you started with can also be ___, using the difference in mass to find the number of ___ of ___.
Determined, moles, water
>Example question: ‘Find n’
BaCl2 n.H2O
The conversion of one substance to another of known chemical composition can be done through ___ or ___ reactions.
Precipitation or volatilisation
>The precipitate should be washed, dried to a constant mass, and weighed.
>In volatilisation, the substance is heated to remove volatile substances and weighed
A volumetric analysis procedure is called a ___.
>A ___ ___ is used to determine the ___ of the other reactant.
Titration,
standard solution, concentration
One solution is measured, ___ (using a ___) into a ___ flask.
The other solution is dispensed from a ___ until a ___ ___ change appears.
Accurately (using a pipette), conical flask
Burette, permanent colour change
A ‘___’ titration is usually carried out first, followed by ___ more ___ titrations, until ___ results are achieved.
Concordant values are within __cm3 of each other.
‘rough’, several, accurate, concordant,
0.1
What is a standard solution?
What can they be directly prepared from?
A solution of accurately known concentration.
A primary standard.
Solutions which are not primary standards require standardisation before they are used. What does standardisation mean?
determining the concentration of the unknown solute in the solution (the concentration of the solution), by titrating it with a standard solution
How do you prepare a standard solution?
1.
2.
3.
4.
- Accurately weigh/measure (with 3dp balance/pipette) the primary standard.
- Dissolve the primary standard in deionized water.
- Transfer quantitatively (‘with rinsings’) to a standard flask
- Make it up to the graduation mark with deionised water. Stopper and invert to create a uniform solution.
List the five properties of a primary standard.
Available in a high purity.
stable as a solid
soluble in water
high GFM
not hydroscopic
Properties of a primary standard:
~Avaliable in a ___ ___.
~Stable as a ___.
~ Soluble in ___.
~Has high enough ___ to reduce ___ ___ when rounding.
~Not h___.
high purity
solid
water
GFM, percentage errors.
Not Hydroscopic (doesnt absorb water)
Give three examples of primary standards.
Sodium Carbonate
Hydrated Oxalic Acid
silver nitrate
Why is NaOH not a primary standard?
Low GFM
Hydroscopic (Absorbs moisture)
What is the difference between the end-point and the equivalence point of a titration?
End-point: Colour change is visible
Equivalence point: Reaction is just complete (not usually visible)
What are the four types of volumetric analysis that you should know?
>They are titrations.
Acid-base titrations.
REDOX titrations.
Complexometric titrations.
Back titrations.
1/4
Acid-base titrations use an acid or ___ of ___ ___ to find the ___ of the unknown (the other one).
A pH ___ is used to detect ___.
acid or base of known concentration, concentration,
pH indicator, neutralisation
2/4
In a REDOX titration, an ___ agent reacts with a ___ ___.
Again, (as in all titrations), the ___ of one solution that neutralises/has an effect on the other solution is ___, and used in ___.
oxidising agent, reduction agent,
volume, recorded (using burette + indicator), calculations
3/4
Complexometric titrations are based on reactions in which ___ ___ are formed.
___ is an important complexometric reagent because it reacts in a _ : _ ratio to form ___ ____.
The concentration of ___ ___ in solution can then be calculated (using ___ of the complexometric reagent).
metal complexes
EDTA, 1:1, metal complexes, metal ions, moles
4/4
Back titrations are used to find the number of ___ of a substance, by reacting it with an ___ volume of reactant, of known ___.
You can then calculate the number of moles of the ___ ___ that is left, by doing a ___.
This allows you to find the number of ___ of excess reactant, that reacted with the ___ ___, and therefore the number of moles of the substance.
moles, excess, concentration
excess reactant, titration
moles, unknown substance
When are back titrations useful?
When trying to determine the quantity of a substance in a solid, that does not dissolve in water.
>So, you use another chemical in excess and find how much of your substance there is by looking at how much of the excess was used
Percentage yield can be calculated by the equation…
actual yield / theoretical yield X 100
What four things reduce percentage yields?
transfer errors
purification
position of equilibrium
side reactions
What is a back titration?
It is when a substance is not titrated itself but instead a compound is reacted with the substance and then the remaining compound is titrated to see how much did not react ie how much was left over.
