Chapter 8 (chemical analysis) Flashcards
what is qualitative analysis?
It allows for identification of a specific substance based on descriptors and observations (eg. colour, smell, sight, state)
What is quantitative analysis?
It determines the quantity of a substance based on numerical values and measurements.
What are the 3 main methods of analytical technologies? Briefly explain each.
- colourimetry (analysis by colour: uses the light absorbed, emitted, or transmitted by the chemical
- gravimetric analysis: uses stoichiometric calculations based on a fixed mass of a reagent
- titration analysis: uses stoichiometric calculations based on the measured solution volume of a reagent
Is colourimetry quantitative or qualitative?
Qualitative
Describe colourimetry (3 points). What tool can be used in the process?
- most aq solutions are colourless
- solutions with monatomic and polyatomic transition ions have a colour
- the colour is due to the ion’s ability to absorb specific wavelengths of light
- a spectrometer can be used
What is a spectrometer?
It is a tool that measures ion concentration and the quantity of light/
Describe flame tests (4 points). Name a tool that can be used
- used to identify metal ions in unknown compounds
- usually group 1 and 2 ions
- the metal ions are heated and release certain wavelengths of visible radiation
- colours are dependent on the energy of electrons in an ion
- a spectrophotometer can be used
What is a spectrophotometer?
It measures different wavelengths.
___________________ is an important part of quantitative analysis.
Precipitation
When does precipitation occur? Why is is not possible to predict the amount of excess required?
Precipitation occurs when a reaction forms a slightly soluble product. It is not possible to predict the amount of excess required because the amount of limited reagent is not known.
What are 4 assumptions we make about a reaction to use stoichiometry?
- spontaneity
- quick
- quantitative
- stoichiometric
________ and ________ is used to ensure precipitation completeness. Explain the process.
trial and error;
- mix equal volumes of each reagent
- allow precipitate to form and settle
- slowly add small amounts of excess with a dropper and watch for a precipitate (cloudiness)
- if cloudiness forms, ass more excess because the reaction is not complete
- no cloudiness means that the limiting reagent is done reacting and the reaction is complete
What is a precipitation reaction?
When a solid forms from mixing liquids
Why is there a limiting reagent?
- a reaction rarely has exactly the right amount of each reactant
- there’s usually left over (excess)
What is the limiting reagent?
The reactant the limits the amount of product created.
What is the excess reagent?
The reactant not completely used up
Which reagent is the controlling one?
The limiting
A reasonable reagent excess to ensure completion of a reaction is _____%
10%
If you are given two amounts of reactants and must determine which is limiting, you should use the _______ _________.
Mole ratio
What is volumetric analysis?
A technique used to find an amount of a certain substance by doing a titration.
Explain a titration. Use the terms titrant, sample, burette, and Erlenmeyer flask.
A titration is adding a certain volume of solution substance with a known concentration (titrant) from a burette into a fixed volume of solution being analyzed (sample), usually in an Erlenmeyer flask.
What is an equivalence point?
When the exact theoretical amount of titrant has been added (the reaction stops and is at its completion)
What is an end point?
An experimental amount that causes an observable change; the point in a titration when a sudden colour change is observed is the end point (titration stopped, volume of titrant determined)
What are some requirements/facts about titrations?
- reaction between titrant and sample
- concentration of at least one reactant must be known
- minimum of 3 trials (the results are averaged for stoichiometry calculations)
- average volume is the endpoint (should coincide with the equivalence point)
What is a standard solution?
The concentration of the solution is accurately known in a standard solution.
What is a primary standard? What state of solute cannot be a primary standard?
Chemical used that can be obtained with high purity and no contaminants (mass can be measured to high accuracy). They are very pure and stable. A gas solute cannot be a primary standard (because the gas will escape when a container the opened).
What is standardizing a solution?
Finding the concentration of a solution after it is prepared, by reacting it with another another solution that has been prepared from a primary standard.
describe a net ionic equation for strong monoprotic acid–strong monoprotic base reactions
- ions other than hydrogen and hydroxide ions are spectators
- OH-(aq) + H+(aq) —> H20(l)
What type of titrations have a pH of 7 at their equivalence points?
Strong acid-base titrations
Describe a titration curve/pH curve
Plotting of the pH of the sample as a function of the amount of titrant added
When the ________ is near, one final drop of the titrant should cause a permanent ______ change if an indicator is used.
end point; colour
what is the inflection point on a pH curve?
The point where the direction of the curvature changes
True or false: when a titration is done, the pH curve does not end at the endpoint, and excess titrant is added to ensure completion
True
Acid-base titrations are found as ________ and __________ curves.
monoprotic; polyprotic
