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Old 05-03-2004, 05:32 AM
Ken Pinard
 
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Default DIY CO2 system question (Correct calculations)

Ok, now I am getting even more curious,

Do you happen to know the volume of 2 mols of CO2? How about the volume
of single bubble from a 1/4" (standard) air line?

Yeh, I've gone off the deep end. I was just thinking that I might be
able to guess the length that a solution could survive and how much CO2
would be available for the tank during that time. Basically, the it won't
change the how often I change the bottles, but I started in Chemistry in
college because I found the numbers intriguing.

Thank you again,

Ken Pinard


"Ken Pinard" wrote in message
...
Hi nice explanation, I do have a couple of questions. Mostly for my own
curious mind.

Since Baking Soda is Basic will it not raise the pH? I know we used it in
chemistry to neutralize the acids (even the stuff I dropped all of the
floor, what a mess ;o)

But since Baking Soda raises the kH, the amount of CO2 that is held in the
water solution will be higher. Thus creating carbonic acid. Which will

lower
the pH.

I wish I remembered my chemistry better, its been 25 years now, I actually
find all these equations fascinating.

As I ponder the effect of alcohol on yeast, while I drink a little wine, I
am wondering what additive can combine with alcohol that will not kill the
yeast or react with CO2? I imagine that the idea has been explored

before.
I just was curious.

Thank you for the explanation and equations, I am going to go over them

with
my old chem books (still got them) and try and get them in my head again.

Ken Pinard (French meaning wine - I have alcohol on the brain


"Morten" wrote in message
...
Folks,

The calculations I did in the previous mail were wrong, I just double
checked them...

Here are the original mail with the right figures...

/Morten


---

The addition of baking soda (2NaHCO3) will not lower the amount of

alcohol
(CH3CH2OH) on the solution unless you put so much if in there that it

lovers
the pH too much below 5 effectually killing the yeast before it gets a
chance to convert the sugar (C6H12O6) to CO2

The chemical reaction (or at least the end result of the yeast's

reduction
of sugar goes like this:

C6H12O6(aq) = 2(CH3CH2OH(aq)) + 2(CO2(g)) + energy (used by yeast)

so, for each mol of sugar you get 2 mol of CO2 and because the molar

weight
of sugar is 180.1572 g/mol and the molar weight of CO2 is 44.0098 g/mol,

you
will get (2 * 44.0098 g/mol) / 180.1572 g/mol = 0.4886 g CO2 for each g

og
sugar.

This is max you can get but because some of the CO2 will stay in the

water
in the yeast reactor you will get a little less than the 0.4886 g CO2 /

g
sugar mentioned above.


Since the molar weight for alcohol (CH3CH2OH) is 46.0688 g/mol you will

get
(2 * 46.0688 g/mol) / (180.1572 g/mol) = 0.5114 g alcohol for each g

sugar
added to the reactor.


But, because the alcohol will kill the yeast if the concentration gets

to
high (depending on which type of yeast is used, common baking yeast will
start to die arround (7% - 8%) we need to make sure that the

concentration
of alcohol is low enough to make sure that all the sugar is consumed

before
the alcohol kills the yeast.


If using 2.0L of water (H2O) = 2000g and 220g og sugar the end

concentration
will be (0.4886 * 220 g ) / (2000 g + 04886 * 220 g) = 0.0533 = 5.33 %

which
will alow the yeast to consume all the sugar and still survive the

alcohol.

Using 220 g of sugar this will yield 0.5114 * 220g = 112.5143 g alcohol

and
0.4886 * 220g = 107.4856 g CO2


When all the sugar is gone the yeast will 'floculate' out of solution

and
sink to the bottom of the yeast container but will not die, so we can

actual
ly re-use the yeast every time we set up another batch of sugar if we
carefully drains the water / alcohol solution from the container and

don't
rinse the container with very hot water killing the yeast in the

process.

In the long run it will benefit the yeast if we used a yeast nutrient

(can
be bought from home brewers shops) to feed the yeast the nutrients that

the
yeast needs to stay healthy for prolonged use.


Because some of the CO2 stays in the water we have a buffer solution

like
this:

CO2 + H2O = H+(aq) + HCO3-(aq)

This process is dependent on temperature and the specific wapor pressure

of
CO2 in the container and the water, but i can't remember how to

calculate
the exact ammount of CO2 in solition given the pressure / temperature of

the
solution, so I'll ignore this bit :-)

When adding baking soda you effectively increases the kH of the solution
which loveres the pH making the environment a little more hostile to the
yeast. If i remember correctly yeast prefers a pH of 5 to 6, but will
survive 4 to 9, so there are some room for pH swings before the yeast

gives
up.

This reaction goes like this:

2NaHCO3 + H2O = 2Na+(aq) + 2HCO3-(aq)


Baking soda can be added to stabilise the pH in the reactor if the water
used have a very lov Kh, but for normal (higher that 4 Kh) water baking

soda
actually makes the conditions for the yeast worse but might prolong the
reaction somewhat purely because some of the yeast will die because of

the
higner pH in the reactor.



I hope this came through as i thought it, if not please dont hesitate to

ask
further questions :-)


Regards

Morten
----



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