Experiment 8. Inclass INVESTIGATION Flashcards
What Component of the salt produce the coloured flame observed?
The Metal in the Salt is what produced the colour in the flame.
Metal atoms usually exist as ions (Cation)
The metal cation in the salt is the reason for the occurrence of the observed colour. The reason as to why cations produce colour is that the wavelength of the emitted photon happens to be in the visible spectrum. The light which is emitted when any atom is placed directly into the flame is due to photon emission. This emission is the result of electron shift process; when excited by energy electron jumps to higher energy level and when rest back to the ground state. Cations emits photon in visible wavelength spectrum, anions also produce coloured flame, it’s just we can’t see them.
Elements which have energy of valence shell that lies in the visible light spectrum are either alkali metals or alkaline earth metals (some transition metals as copper). And they are cations in solution.
What assumption can be made about the ethanol in the flame test?
Ethanol acts a fuel in this experiment.
When the ethanol is ignited the salts will heat up, thus turning the fames a different colour.
A fuel is any material that can be made to react with other substances so that it releases energy
The application of ethanol in the experiment is so that it can act as a fuel. Fuels are substances that burn to give off a relatively large amount of heat. It is the ethanol in the experiment being set aflame and not the salts itself. The salts in the experiment which give off the colours, are enabled to do this due to them being heated by the flame caused by the combustion of ethanol.
Why must a clean watch glass be used for each test.
If the watch glass has not been cleaned before testing the next salt, then there will be contamination between the salts. A sample containing a number of different metals are not suitable for analysis by a flame test as the excitation and emission of light via the flame test will result in a mixture of different colours that will be hard to identify individually.
Explain how the coloured light observed is produced.
The different colours are caused by the different electron transitions occurring in the different atoms. The production of the actual colour within the experiment is caused by ‘metal’ in the salt.
- The ‘excitement’ of an atom or an ion is caused by very strong heating, where the electrons within the atom’s valence shells are promoted from their normal unexcited state into higher orbitals.
- Electrons in an atom can only be found at certain discrete energies, this can be seen by the atom’s electrons being organised into into electron orbitals or shells which only allows the occupation of an electron which fulfils the particular energy level’s characteristics.
- The energy levels of the electrons are described as being ‘Quantised’.
- The lowest energy level state of an atom is called ‘Ground State’, which where the electrons are found normally within an atom, ‘un-excited’.
- During the flame test experiment, the chemical reaction produces energy which the electrons absorb, and becomes ‘excited’, causing them to ‘jump’ to a higher energy level which matches the energy that the electron currently has. The higher energy level state can be defined as the ‘excited state’.
- Electrons do not stay in excited states for very long (this only occurs for nanoseconds),they soon return to their ground states by ‘jumping’ back to their original (ground) energy state or level, emitting a photon with the same energy as the one that was absorbed. When they emit the energy, they emit the discreet “packets” (or particles) of the absorbed energy called photons as ‘electromagnetic radiation’.
- The spacing between energy levels in an atom determines the sizes of the transitions that occur, and thus the energy and wavelengths of the collection of photons emitted and thus the wavelengths emitted by the electrons is what we see as the light in the flame test.
Light can be all different colors, depending on a property of light waves, called wavelength. Wavelength is the distance between peaks on the light waves.
Give practical use for this type of test
This method can be seen in festivals and celebrations through fireworks. The characteristic colours of the fireworks are due to particular metal elements. In this case, the energy to excite the electrons within the atoms comes from the exothermic chemical reaction between oxygen in the air and gunpowder.
- Geologists use the flame test to identify the presence of metals.
- Forensic scientists can use flame tests at crime scenes for quick analysis of elements present.
- Miners use the test for analysis of samples, particularly when prospecting.
Often different colours are used to describe the same flame colour, Eg lilac,mauve, or purple for potassium. Why might this be a problem?
People see colour ‘differently’ meaning they either don’t understand the colour names, or they might associate or perceive these colours differently.
Since this way of measure is ‘qualitatively and not ‘quantitative’ there is not a definitive answer, making a confusion and disagreements on the outcome of the experiment.
This is a problem because not everyone perceives and identifies colour the same way. For some the naming of colours may be every detailed and specific, whereas others identify colours in a very broad or general way. This qualitative way of measurement brings in many different answers and results to the experiment due to the difference of human understanding and perception of colour. This can cause bias leading to disagreements, conflicts and confusion between scientists conducting this experiment as the results and the way of getting to the result is very open-ended and has room for many interpretations. Thus the results of the experiment will not be as precise as possible.
Often different colours are used to describe the same flame colour, Eg lilac,mauve, or purple for potassium. Is this a random or systematic error? Justify your choice.
This problem is an example of systematic error. A systematic error is caused generally by non-calibrated instruments or flawed method. In this case the results of the experiment is not accurate and disagreed upon about the colour of the flame due to the ‘faulted’ method of measurement which was by using the more objective way of measurement; Quantitative measurement.
-However systematic error can be solved by making alterations in the experiment, which in this case means by creating a new method of measurement such as colour chart, where the conductors of the experiment are able to identify colours observed specifically according to the chart.
always affects measurements the same amount or by the same proportion
Safety issues and processes that need to be mentioned
- The use of a flammable liquid; The ethanol used in this experiment is flammable, so being present in a naked flame may result in a fire. To avoid this issue to it essential that amounts used are as indicated, and the stock solution kept away from any naked flame.
- The naked flame conducted in this experiment is also a hazard in itself, as if not managed then it will cause damage to equipment in the room and the clothing/skin on individual. To avoid this issue it is important that the experiment is conducted on a heat proof mat, away from any other equipment, and always managed by one person.
- The salts used in the experiment is also a safety issue factor as some may be corrosive on skin, poisonous if inhaled etc. To avoid any issues with the usage of salts it is important to wear safety glasses, the salt is collected with and transported into the correct equipment, and that particular equipment only. If there is a need to smell the salt (which there isn’t in this case) then only waft the smell to the nose. It is also super important that if the salt comes in contact with skin to immediately wash it of with sanitation liquid and water.
- Exposure of hair to the direct flame. It is a health hazard if loose hair come in contact with the naked flame as it can result in hair being enflamed. It is important that those whom are working with the flame has made sure all loose hair pieces are tied back, to prevent from the safety issue to occur.
Improvements for this flame test
- Inclusion of a colour chart. Since colour determination is a quantitative way of measurement the results attained will be very biased and objective. By using a colour chart within the experiment to use as reference to help with identification of the specific colour. This will not only take away any confusions and disagreements with results, but also help come up with more accurate results.
- Specific measurements of ethanol. Instead of the method directing the conductors of the experiment to use between ‘1-2mL’ of ethanol, it should be more specific with the amount and the particular measuring device. If this was to be applied then any slight alterations of the result due to the amount of ethanol used in the experiment can be removed and thus a better result can be attained.
- Specifications of measurement of salt. Instead of the method directing the experiment conductors with the instructions ‘place a small amount of (pea sized) of salt’ , it should be more specific as to how much salt should be used. ‘Pea sizes’ are different and people’s perception are different, so if a particular amount was specified or a particular measurement device was told to be used, then any small alterations between results can either be minimised or even removed.
What is the difference between systematic error and random error?
A systematic error is an error that occurs in an experiment because of the way the experiment was designed e.g type of Apparatus or experimental method, human judgement
- systematic error can be reduced by trialing the experiment multiple times or even resolved by altering the method.
Random error is an error that comes from measurement with statical fluctuations, due to the precision limitations of the measurement device. Eg. timing of things, atmospheric conditions ect
- random error can be minimised by having conducted the experiment multiple times and averaging the numbers. If an outlier occurs and there is no justification for it be included, then just discard the result.
What is the difference between Quantitive measurement and Qualitative measurement?
Quantative Data is numerical data, from measurement.
Eg Mass,Volume,pH,Temp,Time
Qualitative Data are observations results (not measured) in the form of words,symbols ect Colour,Brightness
Laboratory safety Issues
- behaviour (a conscious or high alert behaviour, no running)
- clothing (enclosed shoes,eye protection)
- Due care( clean up spills, handle with care )
- emergency (know escape routes)
- food and poisons (no consumption of food, wash skin,dispose in specialised way.)
Safe lab practices
- Acids and Alkalies (wash under water for 20min, affected clothing removed, to dilute acids, acid in water not the other way)
- burns (hot BB and glassware handling, yellow flame BB when not in use for a period of time,BB off when not in use)
- Chemical spills ( don’t carry bottle via neck,wash)
- fire (never panic, escape route, fire blankets and extinguisher, no naked flame in flammable location, turn off gas &electric appliances, shut door,raise alarms)
What is an isotope?
Isotopes are atoms with the same number of protons but a different number of neutrons.
The isotopes of an element always have identical chemical properties but differ slightly in their relative atomic mass, density and in nuclear stability (causing some to be radioactive)
What is relative atomic mass?
Relative atomic mass is the average weight of the relative isotopic masses of an element on the scale where carbon-12 is taken as 12 units exactly.
Carbon 12 is the basic measurement that everything is compared to ( as it is a standard).
