Analysis I Flashcards
Purpose of a volumetric flask
Makes up an accurately known volume of solution
Purpose of a volumetric pipette
Dispenses an accurately known volume (aliquot) of a solution
What is an aliquot?
An accurately known volume of a solution
Purpose of a burette
Delivers an accurately known but variable amount of solution
How many decimal places on a volume measurement made with a burette?
Two decimal places, but the second decimal place is always 0 or 5 (ie nearest 0.05mL)
What is a primary standard substance?
A substance that can be prepared pure and dissolved in water to make a solution whose concentration is accurately known
What are the features of a primary standard?
Can be made pure. Does not degrade or react with air. Known molar mass. Preferably dissolves well in water and is inexpensive.
What is a primary standard solution?
A solution containing one solute, that has been prepared by dissolving a known mass of that solute in a known volume of pure water. As a result the concentration is accurately known.
What is the name given to the solution in the burette during volumetric analysis?
Titrant
What is the name given to the solution in the conical flask during volumetric analysis?
Analyte
What name is given to the volume of titrant dispensed into the conical flask during a titration?
Titre
What is the total range of concordant titres?
0.10 mL
What is a mean titre; how is it calculated?
The average of all concordant titres in a titration experiment. Calculated to two decimal places.
What is a dilution factor and how is it calculated?
The final volume divided by the initial volume, where water has been added to dilute a solution.
Why is an indicator added to the analyte before a titration?
The indicator changes colour at or near the equivalence point. This colour change indicates the end point.
What is the equivalence point?
The point at which the exact mole ratio of reactants has been added, according to the balanced equation. At this point neither reactant is in excess.
What is the end point?
The point at which observable experimental evidence shows that the equivalence point has been reached
What is a titration curve?
A graph plotting pH against volume of titrant added
When discussing errors, what is a ‘mistake’ and how should it be treated?
An avoidable error that may cause the experimental result to be inaccurate. Experimental results involving mistakes should be rejected.
When discussing errors, what is a systematic error?
An error introduced by the method or apparatus, that cannot be eliminated by repeating the experiment. This error causes inaccuracy in the same direction for each experiment.
When discussing errors, what is a random error?
An error that may cause the experimental result to be higher or lower than the true value.
How can the effect of random errors be minimised?
Repeat the experiment multiple times and take an average value.
What is the empirical formula of a compound?
A chemical formula showing the simplest whole number ratio between the elements in a compound
What is the molecular formula of a compound?
A chemical formula showing the exact number of atoms of each element in a molecule of that substance.
What is a precipitate?
A solid formed in a reaction between two solutions.
How is heating to constant mass achieved?
A substance is alternately heated and weighed until its mass is the same in multiple measurements (often 3).
Why is heating to constant mass performed?
This ensures that no water is present in the sample
What does an emission spectrum look like?
Coloured lines on a black background
What does an absorption spectrum look like?
Black lines on a coloured background
What is absorbance?
A measure of the intensity of light remaining after some has been absorbed, compared with the intensity of light when none has been absorbed.
What is transmittance?
The opposite of absorbance; A measure of the proportion of light that has been transmitted through a substance (or solution), where 100% transmittance means that no energy has been absorbed.
What name is given to the distance between the same point on two successive waves?
Wavelength
What name is given to the number of waves that pass a given point in one second, and what units are given to this value?
Frequency, measured in Hertz (Hz)
In spectroscopy, what is a cuvette?
A cell or small test tube used to hold the analyte
What is a calibration curve?
A plot of the results of an experiment at a range of known concentrations, so that an unknown concentration within that range can be assessed.
How do you identify the parent or molecular ion (M) peak in Mass Spectrometry? What information does it give us?
The furthest peak to the right (excluding very small peaks). This shows the molar mass of the parent molecule.
How do you identify the base peak in Mass Spectrometry?
The highest peak (most abundant fragment)
Chlorine has two main isotopes, Cl-35 and Cl-37. Identify the molecular ion peaks that would be seen in mass spectrometry of chlorine gas (Cl2).
There would be a peak at m/z = 70 (2 x Cl-35 isotopes), a peak at m/z = 72 (1 x Cl-35 and 1 x Cl-37) and one at m/z = 74 (2 x Cl-37 isotopes)
