Empircal formula ?

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Reply 20

Mr Nonsense

AVAINTEX

lol I Explained the Molecular formula.. Dummy me T_T

why does fividing by 0.4 give you the simplest ratio for ANY question??
ie your step 4 from above...

Reply 21

AVAINTEX

Mr Nonsense

why does fividing by 0.4 give you the simplest ratio for ANY question??
ie your step 4 from above...

in some Empirical Formula Problems You have to do step 4,Because by it you can get the molecular formula and then you can divide by 2 like this previous example the Molecular formula is B4H10 all you have to do is divide the ratio by 2 to get the Empirical formula which is B2H5 :yep:

Reply 22

AVAINTEX

Another Reasonable Reason why you must follow step 4 in my previous post.is that some student predict the number that they want to multiple the result with like

Originally Posted by Woody.
The start of what you've done is right

81.2/10.8 = 7.5 18.8/1 = 18.8

That's a 7.5:18.8 ratio

Divide by the smallest number

7.5/7.5 = 1
18.8/7.5 = 2.5

That's a 1:2.5 ratio

The empirical formula is the simplest whole number ratio, 2.5 is not a whole number

Get it to a whole number by multiplying by 2

That's a 2:5 ratio

Therefore, B2H5

Why did Woody multiple by 2?

what if the ratio was 1:0.24 ??

So i highly recommend you to use My step 4 :yep:

Reply 23

charco

Study Forum Helper

what if the ratio were 3:1.33?

How would dividing by 0.4 help?

Reply 24

AVAINTEX

charco

what if the ratio were 3:1.33?

How would dividing by 0.4 help?

Well,In baby princess previous example i divide 1 by4. i didnt say that the 4 was a constant

3:1.33

divide 1. by .33 =3.0

Molecular formula and the empirical formula for this compound is Y9X4 which means that its the simplest whole ratio.

EF=MF

Reply 25

DeanK2

Yeah - that is just crazy - take 6 : (1/9) etc, and any fraction of the form b/3n and in general that rule does not apply. [In fact there are many more cases such as a/7n, etc, but in an exam it will be expected that a ration involving 3 will come up - I think they are common - don't know about anyone else...).

Reply 26

Woody.

AVAINTEX, I multiplied by two because 2.5 is not a whole number, the definition of the empirical formula is the simplest whole number ratio. To make 2.5 into a whole number, multiply by two.

In A-Level I highly doubt there will be a 1:0.24 ratio. The most complex I've seen is a 1:1.33 where you have to times by 3.

Reply 27

sam161

AVAINTEX

Excuse me But it is not the right way.Ive Already explained how you can solve it.

Extra Empirical formula problem:
Ascorbic acid(vitamin C) Cures scurvy.it is composed of 40.92% carbon,4.58% Hydrogen,54.50% Oxygen.Determine its Empirical Formula.

GOOD LUCK :biggrin:

C3 H4 O3

I'll have a cookie now.

Reply 28

charco

Study Forum Helper

Just for your entertainment...

the most (apparently simple) awkward EF question I've come across on an exam paper is:

Carbon 81.82%, Hydrogen 18.18%

I'd be interested to see the Avaintex method...

Reply 29

Woody.

81.82/12 : 18.18/1

6.82 : 18.18

1:2.67

3:8

Is C3H8 right?

Reply 30

DeanK2

Woody.

81.82/12 : 18.18/1

6.82 : 18.18

1:2.67

3:8

Is C3H8 right?

Yep -

Reply 31

charco

Study Forum Helper

EierVonSatan

*sigh*

???

???

oh! It's gone!

Reply 32

DeanK2

This is getting wierd. Why are there so many insane people on these threads. It's bad enough having EVS, charco and Sengu swoop in before you (even though the post has been unanswered for three hours or so :shifty:

).But I don't see the benefit of putting up a crack pot solution. 0.4. Got it :s-smilie:

Reply 33

charco

Study Forum Helper

It's me again (swoooooop)...

Another little tickler just for fun... here's a question that appeared on the IB HL paper two years ago.

"A compound [name given] consists of the elements carbon, hydrogen and oxygen. Determine its empirical formula if 1.0 g of the compound forms 2.68g of carbon dioxide and 0.657 g of water on complete combustion"

Avaintex method preferred. :smile:

Reply 34

sam161

Is it?

Spoiler

The avaintex 'method' with multiplying by 0.25 is no different to looking at it and thinking, 2.4 is nearly a quarter of 10, so I'll just multiply by four to get a more rounded figure. I wouldn't call step 4 part of any method as it is.

The way he described is the way that I do it, by dividing by the fewest number of moles to get 1:x. Then you simply multiply until you get a round figure.