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# Isomerisation and formula by jamie dawes

Formulae and Isomerism
by

## Jamie Dawes

on 10 May 2010

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#### Transcript of Isomerisation and formula by jamie dawes

Formulae and Isomerism Firstly, Formulae... Empirical formula, the simplest whole-numbered ratio of atoms of each element present
How to approach a question... Analysis of a compound showed the following percentage composition by mass: Na: 74.19%, O: 25.81% [Ar: Na, 23.0 ; 0, 16.0] Find the molar ratio of atoms...
Step 1: Find the ratio, in this case, Na:O Step 2: Percentage of Element 74.19 25.81
---------------------, in this case ----- : ----- (3.226:1.613)
23.0 16.0
Atomic number
Step 3: Divide both sides of the ratio by the lowest amount, in this case 3.226 1.613
----- : ----- (2:1)
1.613 1.613 Step 4: Use the Ratio to form the chemical formula, in this case 2:1 Na2O Molecular Formula: The atual number of atoms of each element in a molecule A compound has the same Empirical formula of CH2 and a relative formula mass, Mr, of 56.0. What is the Molecular formula?
How to approach a question... Step 1: Find the Empirical formula mass of the compound, by adding all the atomic numbers. In this case, 12.0 + (1.0 x 2) = 14.0 Relative Molecular Mass 56.0
Step 2: Find the number of units in a molecule: ----------------------- In this case ---- (4)
Empirical Formula Mass 14.0 Step 3: Use the number of units in a molecule to find formula mass. In this case (4 x CH2)=C4H8 What will this include?

. What types of formulae are there in unit 1?

. The explanation of isomerism Now Isomerism... OCR CHEMISTRY 1) Structural Isomerism Molecules with the same molecular formula but with different structural arrangements of atoms Structural Isomerism can occur in 3 ways... The hydrocarbon chain can be unbranched or branched Butane 2-Methylpropane Butane and 2-Methylpropane have the same molecular formula C4H10 A functional group can be in different positions along the main hydrocarbon chain Both compounds have the same molecular formula, C3H6O The functional group may be different Propanal Propanone Both compounds have the same molecular formula, C3H6O 2) Stereoisomerism Compounds with the same structural formula, but with a different arrangement of the atoms in space E/Z isomerism A type of stereoisomerism in which different groups attached to each carbon of a C=C double bond may be arranged differently in space because of the restricted rotation of the C=C bond. Cis-trans isomerism A special type of E/Z isomerism in which there is a non-hydrogen group and hydrogen on each C of a C=C double bond: the cis isomer (Z isomer) has the H atoms on each carbon on the same side; the trans isomer (E isomer) has the H atoms on each carbon on different sides Question... i) How does the structure of trans-hex-3-ene differ from that of cis-hex-3-ene? ii) Explain why both cis and trans-hex-3-ene react with Br2 to produce the same structural isomer This is just one small stepping stone in the path to success... Answers i) ii) The product does not have a double bond and so the groups can freely rotate to give the same structure. BY JAMIE DAWES
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