# how to work out molarity?? watch

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1. say of ethanol, if you're given the volume and the concentration? u have to find density? say ethnoal mixed with water
2. (Original post by neverbeejail)
say of ethanol, if you're given the volume and the concentration? u have to find density? say ethnoal mixed with water
3. (Original post by Neuth)
say u have 5ml 50% ethanol and in a solution its 1.000ml mineral water and 0.500 ethanol plus 0.5ml yeast how the hell do u do it i know u need to find density of ethanol

(Original post by neverbeejail)
say of ethanol, if you're given the volume and the concentration? u have to find density? say ethnoal mixed with water
(Original post by neverbeejail)
say u have 5ml 50% ethanol and in a solution its 1.000ml mineral water and 0.500 ethanol plus 0.5ml yeast how the hell do u do it i know u need to find density of ethanol
moles = mass/molar mass or moles = concentration x volume (in dm3)

I presume volume would be 2.5ml because it's 50% of 5ml.
As you divide 1cm by 1000 to get dm3, I guess to get dm3 for ml I'd have to divide by 100.
So moles = concentration x volume (in dm3), so moles = 0.500mol dm-3 x 0.0025dm-3 = 0.00125 moles.

Rearranging the moles = mass/molar mass equation gives us
mass = moles x molar mass
Ethanol is C2H6O
mass = 0.00125 x (24 + 6 + 16)
mass = 0.0575g

So density = mass/volume (in cm3)
So density = 0.0575g / 0.25cm3
Spoiler:
Show
You probably don't need to know yet, presuming you're beginning AS.

ethanol
eth- denotes two carbons,
-an- denotes only single bonds,
-ol is the suffix for the -OH group.
A carbon can only have 4 bonds and be stable.
So structural formula is CH3CH2OH
Molecular = C2H6O
6. Havent checked the maths but the chemistry is solid ^^
7. (Original post by XcitingStuart)

moles = mass/molar mass or moles = concentration x volume (in dm3)

I presume volume would be 2.5ml because it's 50% of 5ml.
As you divide 1cm by 1000 to get dm3, I guess to get dm3 for ml I'd have to divide by 100.
So moles = concentration x volume (in dm3), so moles = 0.500mol dm-3 x 0.0025dm-3 = 0.00125 moles.

Rearranging the moles = mass/molar mass equation gives us
mass = moles x molar mass
Ethanol is C2H6O
mass = 0.00125 x (24 + 6 + 16)
mass = 0.0575g

So density = mass/volume (in cm3)
So density = 0.0575g / 0.25cm3
Spoiler:
Show
You probably don't need to know yet, presuming you're beginning AS.

ethanol
eth- denotes two carbons,
-an- denotes only single bonds,
-ol is the suffix for the -OH group.
A carbon can only have 4 bonds and be stable.
So structural formula is CH3CH2OH
Molecular = C2H6O
mate i cant get standard deviation if i didnt do repeat tests of the experiment right?
8. (Original post by neverbeejail)
mate i cant get standard deviation if i didnt do repeat tests of the experiment right?
I'm pretty sure you can, as standard deviation just shows the variation in data about the mean (I think.)
You can get a mean from just one set of data.
9. (Original post by XcitingStuart)
I'm pretty sure you can, as standard deviation just shows the variation in data about the mean (I think.)
You can get a mean from just one set of data.
ur kidding me. how the hell do i add error bars onto it then
10. (Original post by XcitingStuart)

moles = mass/molar mass or moles = concentration x volume (in dm3)

I presume volume would be 2.5ml because it's 50% of 5ml.
As you divide 1cm by 1000 to get dm3, I guess to get dm3 for ml I'd have to divide by 100.
So moles = concentration x volume (in dm3), so moles = 0.500mol dm-3 x 0.0025dm-3 = 0.00125 moles.

Rearranging the moles = mass/molar mass equation gives us
mass = moles x molar mass
Ethanol is C2H6O
mass = 0.00125 x (24 + 6 + 16)
mass = 0.0575g

So density = mass/volume (in cm3)
So density = 0.0575g / 0.25cm3
Spoiler:
Show
You probably don't need to know yet, presuming you're beginning AS.

ethanol
eth- denotes two carbons,
-an- denotes only single bonds,
-ol is the suffix for the -OH group.
A carbon can only have 4 bonds and be stable.
So structural formula is CH3CH2OH
Molecular = C2H6O
0.0025 or 0.025
11. I'll give you an example.

10, 30, 50, 70, 90

44, 47, 50, 53, 56

The mean of both is 50, yet in the first example, the standard deviation is much larger because the values used to calculate the mean are spread out much further.

That is my understanding of it, though there's always the possibility that I'm wrong, so get someone else to confer with.
12. (Original post by neverbeejail)
0.0025 or 0.025
oops, I forgot to finish the last calculation off.

So density = mass/volume (in cm3)
So density = 0.0575g / 0.25cm3
So density = 0.23g cm-3 I suppose
13. (Original post by neverbeejail)
ur kidding me. how the hell do i add error bars onto it then
I have no idea about the error bars. I can interpret those, but not make them.
14. (Original post by The Wavefunction)
Havent checked the maths but the chemistry is solid ^^
Ty. :)
15. Count them.

16. (Original post by XcitingStuart)
I'll give you an example.

10, 30, 50, 70, 90

44, 47, 50, 53, 56

The mean of both is 50, yet in the first example, the standard deviation is much larger because the values used to calculate the mean are spread out much further.

That is my understanding of it, though there's always the possibility that I'm wrong, so get someone else to confer with.
yes i understand that but in your example you have repeats e.g 10,30,50 ETC
what if i literally just have one number??

so at time 0 i get 20 yeast cells, at time 30 i get 40 yeast cells, how can i do a standard deviation if i dont have repeats for an average??
17. (Original post by neverbeejail)
yes i understand that but in your example you have repeats e.g 10,30,50 ETC
what if i literally just have one number??

so at time 0 i get 20 yeast cells, at time 30 i get 40 yeast cells, how can i do a standard deviation if i dont have repeats for an average??
They're not repeats of a test, they're just values in the data for one test.
But I think I get where you're coming from.
I suppose then I'd be no variation about the mean, so SD low/non-existant.
I don't see where that'd happen though.
I'm not sure here.

Is it possible for you to post the entire question?
Edit: Perhaps you can't do a standard deviation here.
I'm really not sure here, so I might very well be wrong with the answer in this post.
18. im ****ed
19. (Original post by XcitingStuart)
They're not repeats of a test, they're just values in the data for one test.
But I think I get where you're coming from.
I suppose then I'd be no variation about the mean, so SD low/non-existant.
I don't see where that'd happen though.
I'm not sure here.

Is it possible for you to post the entire question?
Edit: Perhaps you can't do a standard deviation here.
I'm really not sure here, so I might very well be wrong with the answer in this post.
sir, say i have 0.550ml ethanol and 0.950 water ALSO have 0.5 ml YEAST and i want the molarity, how does the yeast affect the calculation?
20. (Original post by neverbeejail)
sir, say i have 0.550ml ethanol and 0.950 water ALSO have 0.5 ml YEAST and i want the molarity, how does the yeast affect the calculation?
The molarity of what? The ethanol?

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