analytical chem

How to Interpret the Results
The sample is identified by comparing the observed flame color against known values from a table or chart.
Red
Carmine to Magenta: Lithium compounds. Masked by barium or sodium.
Scarlet or Crimson: Strontium compounds. Masked by barium.
Red: Rubidium (unfiltered flame)
Yellow-Red: Calcium compounds. Masked by barium.
Yellow
Gold: Iron
Intense Yellow: Sodium compounds, even in trace amounts. A yellow flame is not indicative of sodium unless it persists and is not intensified by addition of 1% NaCl to the dry compound.
White
Bright White: Magnesium
White-Green: Zinc
Green
Emerald: Copper compounds, other than halides. Thallium.
Bright Green: Boron
Blue-Green: Phosphates, when moistened with H₂SO₄ or B₂O₃.
Faint Green: Antimony and NH₄ compounds.
Yellow-Green: Barium, manganese(II), molybdenum.
Blue
Azure: Lead, selenium, bismuth, cesium, copper(I), CuCl₂ and other copper compounds moistened with hydrochloric acid, indium, lead.
Light Blue: Arsenic and come of its compounds.
Greenish Blue: CuBr₂, antimony
Purple
Violet: Potassium compounds other than borates, phosphates, and silicates. Masked by sodium or lithium.
Lilac to Purple-Red: Potassium, rubidium, and/or cesium in the presence of sodium when viewed through a blue glass.
Limitations of the Flame Test

• The test cannot detect low concentrations of most ions.
• The brightness of the signal varies from one sample to another. For example, the yellow emission from sodium is much brighter than the red emission from the same amount of lithium.
• Impurities or contaminants affect the test results. Sodium, in particular, is present in most compounds and will color the flame. Sometimes a blue glass is used to filter out the yellow of sodium.
• The test cannot differentiate between all elements. Several metals produce the same flame color. Some compounds do not change the color of the flame at all.

Primary Reference: Lange's Handbook of Chemistry, 8th Edition, Handbook Publishers Inc., 1952.

Flame Test Colors

Symbol	Element	Color
As	Arsenic	Blue
B	Boron	Bright green
Ba	Barium	Pale/Yellowish Green
Ca	Calcium	Orange to red
Cs	Cesium	Blue
Cu(I	Copper(I)	Blue
Cu(II)	Copper(II) non-halide	Green
Cu(II)	Copper(II) halide	Blue-green
Fe	Iron	Gold
In	Indium	Blue
K	Potassium	Lilac to red
Li	Lithium	Magenta to carmine
Mg	Magnesium	Bright white
Mn(II)	Manganese(II)	Yellowish green
Mo	Molybdenum	Yellowish green
Na	Sodium	Intense yellow
P	Phosphorus	Pale bluish green
Pb	Lead	Blue
Rb	Rubidium	Red to purple-red
Sb	Antimony	Pale green
Se	Selenium	Azure blue
Sr	Strontium	Crimson
Te	Tellurium	Pale green
Tl	Thallium	Pure green
Zn	Zinc	Bluish green to whitish green

naming o chem

Naming Organic Chemicals

The IUPAC (The international Union of Pure and Applied Chemistry) has produced an accepted naming convention (systematic Nomenclature) for chemicals.. The name includes

a prefix, which describes the substituent a stem , which describes the longest chain a suffix , which describes the compound type

A simple molecule illustrating the naming convention is shown below

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Aliphatic Compounds

An aliphatic compound is any chemical compound belonging to the organic class in which the atoms are not linked together to form a ring.   A major structural groups of organic molecules, the aliphatic compounds include the alkanes, alkenes, and alkynes, and substances derived from them, by replacing one or more hydrogen atoms by atoms of other elements or groups of atoms.

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Alkanes (paraffins)

These saturated hydrocarbons with the general formula C_nH_n+2.    All of these substances end with -ane(the IUPAC suffix) and include those listed below.   The stem names relate to the number of carbon atoms in the molecules as shown below

1 Carbon atom - meth 2 Carbon atom - eth 3 Carbon atom - prop 4 Carbon atom - but 5 Carbon atom - pent 6 Carbon atom - hex 7 Carbon atom - hept

etc.etc.

There is no IUPAC prefix for the alkanes as described here.

The lower members of the series are gases and the higher molecular weight alkanes are waxy solids.  Alkanes are obtained from natural gas and petroleum.

Note; A methyl group is simply CH₃.The straight alkane chains are formed by the successive replacement of the end hydrogen atom by a methyl group as shown below...

Methane (CH₄)......

Ethane (C₂H₆)......

Propane (C₃H₈)......

Butane (C₄H₁₀)......

Pentane (C₅H₁₂)......

Hexhane (C₆H₁₄)......

Heptane (C₇H₁₆)......

etc. etc.

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Alkyl Halides (Haloalkanes)

These are organic compounds in which more one or more hydrogen atoms of the alkane series have been replaced by halogen atoms(atoms with one electron short of stable structure )..Example are chloromethane CH₃Cl, Dibromethane CH₂BrCH₂Br etc.   These can be formed by direct radiation between the constituent substances with ultravoilet light..

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Alkenes

These are unsaturated hydrocarbons that contain at least one double carbon bond.   The general formula for alkenes with only one double bond in the molecule is C_nH_2n where n is the number of carbon atoms in the molecule.

The double bond between two carbon atoms is not twice as strong, -the second bond formed between the carbon atoms is weaker than the first.   Thus, the second bond is more vulnerable to attack by suitable reagents, even under fairly mild conditions.   The reactions of this second bond tend to be addition reactions causing the unsaturated carbon atoms become saturated.   The alkenes are therefore more reactive than alkanes.

The alkenes are highly flammable and burn readily in air, forming carbon dioxide and water,. For example, ethene burns as follows :

C₂H₄ + 3 O₂ ==> 2 CO₂ + 2 H₂O

The first three alkenes are gases, the intermediate alkenes are liquids and higher members of the olefin series are wax like solids at room temperature.    The alkenes are insoluble in water, but are soluble in organic solvents.   The liquids and solids have a density less than water.

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Alkynes

These are unsaturated hydrocarbons that contain at least one triple carbon bond.

The names of all alkynes end in "-yne".      In the case of higher members of the alkene series, the triple bond may be between the terminal carbon atoms of the chain, or may be between internal carbon atoms in the chain.
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Alkyne properties
Alkynes are compounds which have low polarity, and have physical properties that are similar to those of the alkanes and alkenes.

They are insoluble in water. They are quite soluble in the usual organic solvents of low polarity . They are less dense than water. Their boiling points show the usual increase with increasing carbon number. They are very nearly the same as the boiling points of alkanes or alkenes with the same carbon skeletons.

Lewis structures for two alkynes are shown below..

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Aromatic Compounds

Aromatic Compounds

Aromatic compounds are a major class of chemical compounds whose molecular structure includes one or more planar rings of atoms joined by covalent bonds of two different kinds.   The term aromatic was first used in 1860 for a group of hydrocarbons isolated from coal tar and characterised by their strong odours. In chemistry, aromaticity has come to denote the chemical behaviour of this class of molecules.

An aromatic is a organic compound that contains a benzene ring in is molecule or has very similar chemical properties to benzene.  Aromatic compounds are unsaturated yet they do easily complete addition reactions.

Benzene comprises a hexagonal ring of carbon atoms possible lewis structures are shown below.   However in practice the carbon-carbon bonds would not be double and single..they would be would be bonds intermediate between double and single...

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Alcohols (at least one OH group)

All alcohol compounds end with ..ol e.g. methanol, ethanol.

Primary alcohols have two hydrogen atoms on the carbon joined to the -OH groups.   Secondary alcohols have only one hydrogen atom on the carbon joined to the OH group.   Tertiary alcohols have no hydrogen atoms on the carbon attached to the -OH molecule.


For example
The ethanol formula can be written CH₃ CH₂OH
this is a primary alcohol.

The 2- propanol molecule can be written as shown below..This is a secondary alcohol

The molecule "2-methylpropan-ol" can be written as shown below..This is a tertiary alcohol

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Thiols (similar to alcohols except Sulfur (SH) instead of Oxygen

Note: Thio -> sulphur containing

Thiols have an older name "mercaptan" . This relates to their ability to react with mercury.  They are named according to the hydrocarbon e.g ethane thiol C₂H₅SH.

These chemicals generally have a strong odour.  They are, unlike alcohols strongly acidic forming saltlike substances when reacting with metals and alkalis.

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Ethers (at least one Oxygen single bonded to two carbons)

These are usually liquids with pleasant odour , but some aromatic and the higher aliphatic ethers are crystalline solids.   They are insoluable in water but soluble in alcohol and diethyl ether.  The commonest ether diethyl ether is usually simply called ether.  Diethyl ether (ethoxyethene) is an anaesthetic and a very useful organic solvent

These compounds are volatile and highly flammable.

The ethers are made by dehydrating alcohols using sulphuric acid.

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Thioethers- Sulphides (similar to ethers except a Sulfur atom in place of an Oxygen atom)

Thio 0> Suphur containing..
Thioethers are organic compounds containing the group -S- linked to two hydrocarbon groups.   The thioethers are named according to the linked organic molecules.   The organics molecules identified in alphabetic order see examples below.

These compounds are generally more reactive than the related ethers.

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Aldehydes (at least one formyl group -CH=O)

These are organic compound containing the group as shown below attached directly onto another carbon atom.

Methanal (formaldahyde) HCHO is a member of this group although it is not a typical aldehyde.   Aledehydes are normally colourless liquids (aliphatic) or solids ((higher aromatics) with characteristic colours.   These compounds are oxidized to acids and reduced to primary alcohols.

Aldehydes are formed by oxidation of primary alcohols.

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Ketones (at least on keto group C=O)

Chemistry naming conventions always end this range of chemicals with -one Where Aldehydes have the C=O group (carbonyl) on an end carbon atom Ketones have it on a middle carbon atom. Secondary alcohols can be oxidixed into ketones.

Acetone (propanone) as shown below is the simplest ketone.  It is made by the oxidation of propan-2-ol .   It is a solvent and is used in the manufacture of plastics.

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Carboxylic Acids (at least one carboxyl group -COOH))

These include at least one carboxyl group -COOH as shown below

Typical carboxylic acids include methanoic (formic) acid (HCOOH->HCO₂H), ethanoic acid-acetic acid (CH₃COOH), butanoic acid (CH₃CH₂CH₂COOH ).   Because carboxylic acids have both a lone oxygen and an OH group, they are strongly hydrogen-bonded to each other, therefore having high boiling points.
Because a large number of carboxylic acids occur naturally in fats and oils these are therefore also known as "fatty acids". The carboxyl group is weakly acidic and all carboxylic acids neutralize OH-.

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Esters

Esters are organic compounds formed by reactions between alcohols and acids .  Esters containing simple hydrocarbon groups are volatile fragrant substances used as flavourings in the food industry.   In esters one of the oxygens has a double bond the other oxygen atom is bonded to a carbon atom of a hydrocarbon.   >/p>

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Amines (at least one Nitrogen bonded to Hydrogen or carbon atoms)

These organic compounds are produced by replacing one or more of the hydrogen atoms in ammonia with an organic group.

Amines are classified as primary, secondary, or tertiary depending on whether one, two, or three of the hydrogen atoms of ammonia have been replaced by organic groups.   Diamines, triamines, and polyamines contain two, three, or more nitrogen groupings of the types identified.

Amines are alkaline to various levels of intensity.   Amines can be aliphatic or aromatic in nature..

Aniline, ethanolamines, and numerous other amines are major industrial chemicals used in making rubber, dyes, pharmaceuticals, and synthetic resins and fibres and in a host of other applications.

The lower molecular weight amines have a fishy-putrid odour.  The aliphatic amines have densities 600 to 800 kg/m³ and aromatic amines have densities about + 1000kg/m³.

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Amino Acids (at least one amino group NH₂ and one carboxyl group -COOH)

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A large group of organic compounds containing both the carboxyl group COOH and the amino group NH₂.  These include Glycine H₂NCH₂COOH.  Many proteins are built up entirely of amino acid groupings by condensation between the NH₂ and COOH groups.
The amino acids are colourless, crystalline substances which melt with decomposition.  They are mostly soluble in water and insoluble in alcohol.

The two simplest amino acids are shown below:...

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Carbohydrates (at least several OH groups and a formyl or keto group)

A group of organic compounds based on the general formula C _x(H ₂O) _y.   The simplest carbohydrates include sugars (saccharides)including glucose and sucrose.

Carbohydrates perform vital roles in living organisms .  Sugars, including glucose, and their derivatives are essential intermediates in the conversion of food to energy.   Starch and other saccharides serve as energy stores in plants.....

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Organometallics (with an ionic bonding between a metal and a carbon structure)

These are compounds in which metals ions or atoms are bound to organic groups via a carbon to metal bond. These may have single metal to carbon bonds as in Aluminium Alkyls (Al(CH₃)₃.   The compounds can also be more complicated double bonds...

A more precise description is "Organometallics relates to compounds in which an organics group is attached through carbon to an atom which is less electronegative than carbon."

Organometallics predates organic chemistry and is now one of the largest forms of chemistry mainly in the petrochemical industry.   This chemistry breaks down the barriers between organic and inorganic chemistry.

It is recommended that further reference on this topic is made to Organometallics

aromatic carrbon

THE NAMES OF AROMATIC COMPOUNDS This page looks at the names of some simple aromatic compounds. An aromatic compound is one which contains a benzene ring. It assumes that you are reasonably confident about naming compounds containing chains of carbon atoms (aliphatic compounds).
	Note:  If you aren't sure about naming aliphatic compounds follow this link before you go on.
Naming aromatic compounds isn't quite so straightforward as naming chain compounds. Often, more than one name is acceptable and it's not uncommon to find the old names still in use as well. Background The benzene ring All aromatic compounds are based on benzene, C6H6, which has a ring of six carbon atoms and has the symbol: Each corner of the hexagon has a carbon atom with a hydrogen attached.
	Note:  If you don't understand this structure, it is explained in full in two pages on the structure of benzene elsewhere in this site. Following this link could well take you some time!
The phenyl group Remember that you get a methyl group, CH3, by removing a hydrogen from methane, CH4. You get a phenyl group, C6H5, by removing a hydrogen from a benzene ring, C6H6. Like a methyl or an ethyl group, a phenyl group is always attached to something else. Aromatic compounds with only one group attached to the benzene ring Cases where the name is based on benzene chlorobenzene This is a simple example of a halogen attached to the benzene ring. The name is self-obvious. The simplified formula for this is C6H5Cl. You could therefore (although you never do!) call it phenyl chloride. Whenever you draw a benzene ring with one other thing attached to it, you are in fact drawing a phenyl group. In order to attach something else, you have to remove one of the existing hydrogen atoms, and so automatically make a phenyl group. nitrobenzene The nitro group, NO2, is attached to a benzene ring. The simplified formula for this is C6H5NO2. methylbenzene Another obvious name - the benzene ring has a methyl group attached. Other alkyl side-chains would be named similarly - for example, ethylbenzene. The old name for methylbenzene is toluene, and you may still meet that. The simplified formula for this is C6H5CH3. (chloromethyl)benzene A variant on this which you may need to know about is where one of the hydrogens on the CH3 group is replaced by a chlorine atom. Notice the brackets around the (chloromethyl) in the name. This is so that you are sure that the chlorine is part of the methyl group and not somewhere else on the ring. If more than one of the hydrogens had been replaced by chlorine, the names would be (dichloromethyl)benzene or (trichloromethyl)benzene. Again, notice the importance of the brackets in showing that the chlorines are part of the side group and not directly attached to the ring. benzoic acid (benzenecarboxylic acid) Benzoic acid is the older name, but is still in common use - it's a lot easier to say and write than the modern alternative! Whatever you call it, it has a carboxylic acid group, -COOH, attached to the benzene ring. Cases where the name is based on phenyl Remember that the phenyl group is a benzene ring minus a hydrogen atom - C6H5. If you draw a benzene ring with one group attached, you have drawn a phenyl group. phenylamine Phenylamine is a primary amine and contains the -NH2 group attached to a benzene ring. The old name for phenylamine is aniline, and you could also reasonably call it aminobenzene. Phenylamine is what it is most commonly for UK-based exam purposes.
	Note:  In all cases where there is some possibility of alternative names, you need to know what your examiners are likely to call a particular compound. Refer to your syllabus and recent exam papers. If you are working to a UK-based syllabus for 16 - 8 year olds, and haven't got these, follow this link to find out how to get hold of them.
phenylethene This is an ethene molecule with a phenyl group attached. Ethene is a two carbon chain with a carbon-carbon double bond. Phenylethene is therefore: The old name for phenylethene is styrene - the monomer from which polystyrene is made. phenylethanone This is a slightly awkward name - take it to pieces. It consists of a two carbon chain with no carbon-carbon double bond. The one ending shows that it is a ketone, and so has a C=O group somewhere in the middle. Attached to the carbon chain is a phenyl group. Putting that together gives: phenyl ethanoate This is an ester based on ethanoic acid. The hydrogen atom in the -COOH group has been replaced by a phenyl group.
	Note:  If you aren't happy about naming esters, follow this link before you go on.
phenol Phenol has an -OH group attached to a benzene ring and so has a formula C6H5OH. Aromatic compounds with more than one group attached to the benzene ring Numbering the ring Any group already attached to the ring is given the number 1 position. Where you draw it on the ring (at the top or in any other position) doesn't matter - that's just a question of rotating the molecule a bit. It's much easier, though, to get in the habit of drawing your main group at the top. The other ring positions are then numbered from 2 to 6. You can number them either clockwise or anti-clockwise. As with chain compounds, you number the ring so that the name you end up with has the smallest possible numbers in it. Examples will make this clear. Some simple examples Substituting chlorine atoms on the ring Look at these compounds: All of these are based on methylbenzene and so the methyl group is given the number 1 position on the ring. Why is it 2-chloromethylbenzene rather than 6-chloromethylbenzene? The ring is numbered clockwise in this case because that produces a 2- in the name rather than a 6-. 2 is smaller than 6.
	Warning!  You will find all sorts of variations on this depending on the age of the book you look it up in, and where it was published. What I have described above isn't in strict accordance with the most modern interpretation of the IUPAC recommendations for naming organic compounds. The names should actually be 1-chloro-2-methylbenzene, 1-chloro-3-methylbenzene, and so on. The substituted groups are named in alphabetical order, and the "1" position is assigned to the first of these - rather than to the more logical methyl group. This produces some silly inconsistencies. For example, if you had the exactly equivalent compounds containing nitro groups in place of the chlorines, the names would change completely, to 1-methyl-2-nitrobenzene, 1-methyl-3-nitrobenzene, etc. In this case, the normal practice of naming the hydrocarbon first, and then attaching other things to it has been completely wrecked. Do you need to worry about this? NO! It is extremely unlikely that you would ever be asked to name these in an exam, and it is always easy to write a structure from one of these names - however illogical it may be! There is a simple rule for exam purposes. Unless you are specifically asked for the name of anything remotely complicated, don't give it. As long as you have got the structure right, that's all that matters.
2-hydroxybenzoic acid This might also be called 2-hydroxybenzenecarboxylic acid. There is a -COOH group attached to the ring and, because the name is based on benzoic acid, that group is assigned the number 1 position. Next door to it in the 2 position is a hydroxy group, -OH. benzene-1,4-dicarboxylic acid The di shows that there are two carboxylic acid groups, -COOH, one of them in the 1 position and the other opposite it in the 4 position. 2,4,6-trichlorophenol This is based on phenol - with an -OH group attached in the number 1 position on the ring. There are 3 chlorine atoms substituted onto the ring in the 2, 4 and 6 positions. methyl 3-nitrobenzoate This is a name you might come across as a part of a practical exercise in nitrating benzene rings. It's included partly for that reason, and partly because it is a relatively complicated name to finish with! The structure of the name shows that it is an ester. You can tell that from the oate ending, and the methyl group floating separately from the rest of the name at the beginning. The ester is based on the acid, 3-nitrobenzoic acid - so start with that. There will be a benzene ring with a -COOH group in the number 1 position and a nitro group, NO2, in the 3 position. The -COOH group is modified to make an ester by replacing the hydrogen of the -COOH group by a methyl group. Methyl 3-nitrobenzoate is therefore:

solubility &reactivity

Solubility and Reactivity of Alkanes, Alkenes and Aromatic Compounds Course Notes

Hydrocarbons: Alkanes, Alkenes, Alkynes and Aromatic

Hydrocarbons are organic molecules made up of only carbon and hydrogen. If the hydrocarbon has only single bonds between the carbon atoms , it is said to be an alkane. If there is a double bond between two carbon atoms, then the molecule is said to be an alkene. When there is a triple bond between two carbon atoms, that molecule is called an alkyne.
Benzene is a special case because there are three alternating double bonds within the six carbon ring, presenting chemical and physical properties that are not possessed by either alkanes or alkenes. Hydrocarbons with a benzene like ring within them are said to be aromatic hydrocarbons

London Dispersion Intermolecular Force

The forces that hold molecules together in a liquid, solid and solution phases are very weak. They are generally called London dispersion forces.
The electrons in the orbitals of a molecule are free to move around. If you could compare a "snapshot" of the molecule at an instant in time, you would see that there would be slightly different charge distributions caused by the different positions of the electrons in the orbitals. The amount of difference is based on the polarizability of the molecule, which is a measure of how well electrons can move around in their orbitals. In general, the polarizability increases as the size of the orbital increases; since the electrons are further out from the nucleus they are less strongly bound and can move about the molecule more easily.
When two molecules come together, these variations in charge can create a situation where one end of a molecule might be slightly negative and the other end of that molecule could be slightly positive. This would result in a slight attraction of the two molecules (until the charges moved around again) but is responsible for the attractive London dispersion forces all molecules have.
These London dispersion forces are weak, the weakest of all the intermolecular forces. Their strength increases with increasing size and polarizability of the molecule.

Hydrocarbon Solubility

The rule to use when determining hydrocarbon solubility is: Like dissolves like.
This means that polar compounds (water, alcohols, and carboxylic acids) dissolve other polar compounds. Water can be broken down into H - OH, thus it has the -OH group which identifies alcohol and carboxylic acids. Nonpolar compounds dissolve other nonpolar compounds but tend not to dissolve polar compounds.
When you test for solubility you are looking for either a homogeneous solution or a heterogenous solution. Homogeneous solutions have no layers evident indicating the hydrocarbon being tested is soluble. These hydrocarbons are miscible. Heterogenous solutions have layers evident indicating the hydrocarbons are insoluble. These hydrocarbons are immiscible.

Hydrophobic - Hydrophilic

When you are trying to evaluate the solubility properties of alcohols and carboxylic acids, it becomes necessary to consider the relative sizes of the hydrocarbon and water-like portions of the molecule. The hydrocarbon portion is said to be hydrophobic (water hating) because it will not hydrogen bond with water but does tend to dissolve in hydrocarbon liquids. The water-like alcohol and carboxylic acid groups hydrogen bond with water and are said to be hydrophilic (water-loving).
If the ratio of the size of the hydrophilic portion to the hydrophobic portion is small, the hydrophilic portion is too small to carry the molecule into solution with water. If the ratio is large, it can carry the molecule into solution.
The solubility of alcohols and carboxylic acids in water is made smaller when the hydrophobic portion of the molecule is made larger.
When determining the solubility of a molecule there is one final rule.
The solubility of hydrogen bonding molecules is improved if either the positive charge on the hydrogen is made larger or the negative charge on the electronegative atom (oxygen or nitrogen) is increased.

Unsaturation and Alkanes and Alkenes

Alkanes are considered saturated because they have only single C-C bonds and cannot add a hydrogen. Alkenes are unsaturated because they are capable of adding a hydrogen when the C=C double bond is broken.

Bromine Test for Hydrocarbon Reactivity

The bromine test is used to determine if the colorless organic compound contains any double C=C bonds (the alkene functional group). Bromine does not react with an alkane because the alkane contains only single C-C bonds which cannot add the bromine. Alkanes merely dilute the red-brown bromine color to an orange or yellow color in the absence of a strong catalyst.
Due to their C=C double bonds which can be broken, alkenes react readily with bromine to produce saturated dibromoalkanes. When an alkene is reacted with bromine, the red-brown color of the bromine is immediately lost due to the reaction of the bromine.



Alkane + bromine (No strong light or heat) results in diluted solution colored orange or yellow indicating no reaction.
Alkane + bromine (heat or strong light acting as a catalyst) results in the brown red color of bromine slowly disappearing.
Alkene + bromine results in the red brown color of bromine rapidly or immediately disappearing giving a colorless solution
Aromatic hydrocarbon + bromine (no heat or light acting as a catalyst) results in no reaction and the red brown color of bromine is diluted to orange or yellow.
Aromatic hydrocarbons are too stable to react without a catalyst so they act like alkanes.

Red brown color of bromine

Bromine Test (left) No reaction, saturated, (right) Reaction, unsaturated






If an alkene is present, the π bond breaks and bromine is added in two places.

Cholesterol

Cholesterol has only one -OH group which is polar. This single alcohol functional group does not make it polar enough to dissolve in water or blood (made up of mostly water). Since cholesterol is not polar enough to dissolve in water it will dissolve in nonpolar solvents. Cholesterol when tested with the bromine test will react, losing the red-brown color of bromine and turning colorless. This is due to the one double (π) bond. This double bond can break allowing bromine to be added, indicating an alkene is present and cholesterol is unsaturated allowing the red brown color of bromine to slowly disappear.

Red brown color of bromine slowly disappears = unsaturated.
Red brown color of bromine dilutes to yellow or orange = saturated.

Bromine test for Unsaturation

Again bromine is used to determine whether an alkane, alkene, or aromatic hydrocarbon is present. If the substance is an alkene it will react with the bromine, indicating the compound is unsaturated. When the red-brown color of bromine disappears it indicates the substance is unsaturated and a reaction has occurred.

ALKANES contain only σ (single C-C) bonds and cannot add any Br so red brown color of bromine dilutes to yellow or orange = saturated.
ALKENES contains a π bond making it possible to add Br so the red brown color of bromine disappears rapidly or immediately = unsaturated.
AROMATIC HYDROCARBONS are extremely stable and will not react without a catalyst = saturated.
When the red-brown color of bromine is diluted to yellow or orange (no reaction), the substance is saturated.

Red-brown color of bromine is diluted to yellow or orange (no reaction), the substance is SATURATED.
Red brown color of bromine disappears (reaction), the substance is UNSATURATED.
Digital Video from DVAction of the Bromine Test for Alkenes

Baeyer Test for Unsaturation

The Baeyer reagent is a cold dilute aqueous solution of potassium permanganate which is a deep purple color. Potassium permanganate does not react with alkanes because they are saturated (single bonds which are all taken). When it is added to alkanes the purple color does not change. However, when it is added to an alkene, the purple color slowly disappears and a brown MnO₂ precipitate forms. The appearance of the brown precipitate indicates a positive test for unsaturation. The Baeyer test for unsaturation is used when the color of the organic compound may interfere with the result of the Bromine Test for Unsaturation.

Purple color dilutes to light purple = SATURATED.
Purple color disappears and brown ppt forms = UNSATURATED.

The purple color of KMnO₄

Baeyer Test for Unsaturation (left) purple diluted to light purple: saturated, (right) purple disappears, brown preciptate forms: unsaturated.