Organic Chemistry for Beginners Quiz

Quiz Answer Key and Fun Facts

1. The world of organic chemistry is vast, simply because carbon has the property of easily being able to form bonds with other carbon atoms, creating a wide range of molecules of various levels of complexity. What is this property of carbon called?

Answer: Catenation

Carbon atoms are tetravalent, which means it has 4 electrons in its outermost shell. Hence, the property of catenation is observed in carbon atoms, leading to a large number of possibilities for bond formation, as a result of which there are so many, many, different types of organic compounds. Other tetravalent elements are silicon and germanium.

The word 'catenation' is derived from the Latin word 'catenare', which means 'to connect in a series' or 'to link'.

2. As is obvious from the name, 'hydrocarbons' are compounds which contain only carbon and hydrogen. Hydrocarbons are of two types- open-chained and close-chained, of which open-chained hydrocarbons are more commonly found. Close-chained (or cyclic) hydrocarbons containing alternating single and double bonds are generally known to have intense smells, which led to this class of compounds being given a special name. What is this name?

Answer: Aromatic hydrocarbons

Ever heard of benzene (C6H6)? Benzene is the simplest possible aromatic hydrocarbon, and consists of 6 carbon atoms arranged in a hexagonal shape, with a hydrogen atom bonded with each of the carbon atoms. The bonds between the carbon atoms are alternately single and double bonds. The structure of a benzene molecule is called a 'benzene ring', because, like I said before, the carbon atoms have formed a kind of hexagonal ring.

Open-chain hydrocarbons are 'aliphatic hydrocarbons'.

3. Moving on to open-chain hydrocarbons now- in saturated hydrocarbons is it true that all the bonds between carbon atoms are single bonds only?

Answer: Yes

In saturated hydrocarbons, only single bonds exist between two carbon atoms, there aren't any double or triple bonds. Saturated hydrocarbons are more commonly known as 'alkanes'. The names of all alkanes and with the suffix "-ane", such as 'methane', 'ethane', and 'propane'.

At standard temperature and pressure (273.15 K temperature and 1 atm pressure), CH4 to C4H10 alkanes are gaseous; from C5H12 to C17H36, they are liquids; and after C18H38, they are solids.

4. Which hydrocarbon, with the formula 'CH4', is the simplest alkane?

Answer: methane

Methane is a gas at room temperature, and is the principal component of natural gas, usually found in petroleum fields. The burning of methane produces little pollution, and hence the use of methane as a fuel, in the form of bio-gas, is encouraged. Bio-gas is particularly popular in rural areas of Denmark and the Netherlands, and is manufactured by the decomposition of organic plant and animal waste by anaerobic microbes.

Methane is also called the 'marsh gas', as it is formed in marshy or swampy areas, where organic matter is left to decay.

It is, however, a strong green-house gas, having the ability to cause 22 times the amount of warming done by carbon dioxide. It is also the the primary gas released along with carbon dioxide and sulphur compounds during...er...flatulation!

5. Alkanes all have a certain 'general' or 'skeleton' formula: Suppose the number of carbon atoms in an alkane is 'n', what is the formula of that hydrocarbon?

Answer: C(n)H(2n + 2)

Let's verify this formula with the help of a couple of alkanes:

Methane (CH4)
Here, n = 1
& (2n + 2) = 2*1 + 2 = 4

Ethane (C2H6)
Here, n = 2
& (2n + 2) = 2*2 + 2 = 6

6. The common names of alkanes, alkenes and alkynes, all begin with certain prefixes, depending on the number of carbon atoms present in them. For example, when there is 1 carbon atom present, the prefix given is "meth-". When there are 2 carbon atoms, the prefix given is "eth-", and when there are 3 carbon atoms, the prefix "prop-" is attached. What is the prefix when there are *4* carbon atoms present?

Answer: but-

A simple table showing the relation between the number of carbon atoms present and the first part of the hydrocarbon name:

1 - meth-
2 - eth-
3 - prop-
4 - but-
5 - pent-
6 - hex-
7 - hept-
8 - oct-
9 - non-
10 - dec-

7. The tricky part of hydrocarbon-nomenclature is when you come across molecules with the same molecular formula, yet different structure! Even though such compounds have the same chemical formula, the arrangement of atoms within one molecule can be different, altering the properties completely! What are these compounds called?

Answer: Isomers

For example, butane (C4H10) has 2 isomers- n-butane (butane) and isobutane (2-methyl propane).

And this is why we have to resort to IUPAC (International Union of Pure and Applied Chemistry) nomenclature... Note that here the names outside brackets are the 'common' names and those within brackets are IUPAC names.

8. Which of the following chemical formulae does NOT represent an alkene?

Answer: C2H2

The general formula for alkenes is C(n)H(2n), where 'n' is the number of carbon atoms present. In C2H2, you can see that the number of hydrogen atoms is not twice the number of carbon atoms present- hence, it isn't an alkene. C2H2 (ethyne), is actually an alkyne, as it contains a carbon-carbon triple bond.

9. Carbon has the unique ability to form long chains with other carbon atoms. What name is given to a long chain consisting of many identical smaller molecules (called monomers)?

Answer: Polymers

Plastics, like polythene (polyethylene) are all polymers. Polythene, for example, is formed by a chain containing a countless number of ethene (C2H4) molecules.

Another example of polymers are proteins, which are polymers of amino acids, said to be the 'building-blocks' of proteins.

10. What is the atomic number of carbon? (Remember, its valency is 4.)

Answer: 6

Carbon has the atomic number 6, as a result of which its electronic configuration is (2,4), giving it its unique property of catenation- the cause of the wonderful world of organic chemistry!

Have a nice day!

Source: Author achernar

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