Experimental technique and equipment Flashcards
What can time be measured with and what units are used?
Time can be measured using a stopwatch or stopclock which are usually accurate to one or two decimal places. The units of time normally used are seconds or minutes although other units may be used for extremely slow reactions (e.g. rusting).
What can temperature be measured with and what is the unit?
Temperature is measured with a thermometer which can normally give readings to the nearest degree Celsius.
What are the 2 types of thermometers available and what are their advantages and disadvantages.
Digital thermometers are available which are more precise (finer detail) than traditional thermometers. However, traditional thermometers rely upon the uniform expansion and contraction of a liquid substance with temperature; they tend to be more accurate than digital thermometers which often need to be re-calibrated.
What is used to measure mass and what unit is typically used?
Mass is measured using a digital balance which normally give readings to two decimal places. These must be tared (set to zero) before use. The standard unit of mass is kilograms (kg) but in chemistry grams (g) are most often used.
What are the 3 main types of equipment used to measure the volume of a liquid depending on the accuracy needed?
For approximate volumes where accuracy isn´t an important factor, measuring cylinders are used. These are graduated (have a scale so can be used to measure) and are available in 25 cm3, 50 cm3, 100 cm3 and 250 cm3. Pipettes are the most accurate way of measuring a fixed volume of liquid, usually 10 cm3 or 25 cm3. Burettes are the most accurate way of measuring a variable volume of liquid between 0 cm3 and 50 cm3 (e.g. in a titration)
What is this piece of equipment called?
A burette
What is this piece of equipment called?
A conical flask.
What is this piece of equipment called?
A volumetric pipette.
What is this piece of equipment called?
A pipette filler
Name the equipment used to measure the volume of gas given off by a mixture in a conical flask.
Conical flask, tube, bung, measuring syringe.
(A graduated cylinder inverted in water may also be used, provided the gas isn’t water-soluble
If the gas happens to be heavier than air and is colored, the cylinder can be used upright)
Decribe the retention factor as used in chromatography
Retention factor = distance moved by compound ÷ distance moved by solvent.
The Rf value is a ratio and therefore has no units.
e.g. the solvent moves 10cm up the paper. compound moves 7cm up the paper the retention factor (Rf) is 0.7.
The Rf value of a particular compound is always the same.
These Rf values are used to identify the components of mixtures
How can melting and boiling points be used to determine purity?
elements and compounds have precise melting and boiling points. If they melt and boil at different temperates than are expected then they are impure and are a mixture.
Melting and boiling point analysis is routinely used to assess the purity of food and drugs
For example, if a sample of water melts at exactly 0°C and boils at exactly 100°C then the water is pure
If the melting and boiling points of the water aren’t these exact values then the water must be impure and contain other substances i.e. it must be a mixture
How does a locating agent work in chromatography?
For chromatography to be useful the chemist needs to be able to see the components move up the paper, which is not the case for invisible samples such as proteins
Locating agents are substances which react with the sample and produce a coloured product which is then visible
The chromatogram is treated with the agent after the chromatography run has been carried out, making the sample runs visible to the naked eye
Are the samples to be tested placed on the pencil line in chromatography?
Yes
A pencil line is drawn on chromatography paper and spots of the sample are placed on it.
Why is a pencil line used rather than ink in chromatography?
Pencil is used for this as ink would run into the chromatogram along with the samples.
