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Reflux (1 Viewer)

AnAn

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1) what are the advantages of refluxing?

2) a compound consists of carbon, oxygen and hydrogen only. the percentage composition by mass of these elelments in the compund is: C ( 54.5%), H (9.2%), O ( 36.3%)
a) Determind the empirical formula of the compound

b) if the molecular weight of the compund was 88.10g/mol, how do i know the molecular formula of the compound

c) it was noted that the compund had a fruity smell, what is a possible name for this compund?
 

Xayma

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1) As esterification (at least at the HSC level) is carried out at near the boiling point of the alkonol, therefore a large amount of gas would be lost to vapourisation, refluxing condenses this gas and allows more of the reaction to take place.

2) a) Consider if you had 100g of this compound:
Therefore you would have 54.5g of carbon, 9.2g of Hydrogen and 36.3g of Oxygen

n<sub>C</sub>=54.5/12.01
=4.538mol
n<sub>H</sub>=9.2/1.008
=9.127mol
n<sub>O</sub>=36.3/16
=2.269mol

n<sub>C</sub>:n<sub>H</sub> =approx= 1:2
n<sub>C</sub>:n<sub>O</sub> =approx= 2:1

Therefore the ratio of C:H:O = 2:4:1
Therefore the empirical formula is C<sub>2</sub>H<sub>4</sub>O

b) C<sub>2</sub>H<sub>4</sub>O has a molecular weight of 44.05g/mol

Now the molecular weight of the formula = 88.10g/mol.

88.10g/44.05g=2
Therefore the moleuclar formula is C<sub>2*2</sub>H<sub>4*2</sub>O<sub>1*2</sub>
C<sub>4</sub>H<sub>8</sub>O<sub>2</sub>
 

AnAn

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thx~~
i have few more questions ask ..

1) why are boiling chips often added to the mixture??

2) are methene, methanol and methanoic acid members of an homologus series?? if not, can u explain why?
 

Xayma

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2) No they dont have the same functional group.
 

CM_Tutor

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1. When discussing refluxing, make sure you can explain both the heating and the use of reflux. ie, with esterification, heat to:

* increase the rate of reaction - alcohol + carboxylic acid esterifications arre generally slow
* increase the yield - HSC esterifications are endothermic equilibrium processes, and so heating drives the reaction to the right (Le Chatelier's Principle)

Having decided to heat, the presence of volatile (easily vapourised) materials makes the use of a reflux apparatus essential, to prevent their loss.

2. Xayma has explained with the MF is C<sub>4</sub>H<sub>8</sub>O<sub>2</sub>, so I'll just address part (c). The question mentions a fruity smell - this means that the product is almost certainly an ester. The possible esters with this molecular formula are:

methyl propanoate: CH<sub>3</sub>CH<sub>2</sub>-C(=O)-O-CH<sub>3</sub>
ethyl ethanoate: CH<sub>3</sub>-C(=O)-O-CH<sub>2</sub>CH<sub>3</sub>
propyl methanoate: H-C(=O)-O-CH<sub>2</sub>CH<sub>2</sub>CH<sub>3</sub>
2-propyl methanoate: H-C(=O)-O-CH(CH<sub>3</sub>)<sub>2</sub>

3. Boiling Chips (or anti-bumping granules) are included prmarily as a safety measure. They prevent the liquid from superheating, and thus prevent bumping. They do serve other functions (like helping with the uniformity of heating, as Xeriphic suggests), but the safety feature is their major role.

4. No. The alkanes - methane, ethane, propane, butane, ... - are a homologous series, as are the primary alkanols - methanol, ethanol, 1-propanol, 1-butanol, ..., and the alkanoic acids - methanoic acid, ethanoic acid, propanoic acid, ... So, methane, methanol and methanoic acid belong to different homologous series. A simple way to think of a homologous series is that it can be represented by a general formula, ie:

alkanes: C<sub>n</sub>H<sub>2n+2</sub>, n = 1, 2, 3, ...
primary alkanols: C<sub>n</sub>H<sub>2n+1</sub>OH, n = 1, 2, 3, ...
alkanoic acids: C<sub>n</sub>H<sub>2n+1</sub>COOH, n = 0, 1, 2, ...

AND that each member differs from the preceeding member by a CH<sub>2</sub> unit
 

spice girl

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hazard warning:

methanoic acid is found in all soft drinks in high concentrations! its reduced form, methanal (a.k.a formaldehyde) is a known carcinogen (cancer-causing substance)!
 

Xayma

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Methanoic acid is found in soft drinks? I thought it was just Carbonic acid.
 

Xayma

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Doesnt Carbonic acid have three oxygens and methanoic only two though?
 

spice girl

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oh yea....

oops

gee my maths is so crap now i can't count to 3

stoopid med

it's brainwashing me
 

CM_Tutor

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AFAIK, methanoic acid (or formic acid) is not found in soft drinks, although carbonic acid and benzoic acid are. Formic acid is the acid in some ant stings.
 

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