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DIY CO2 system question (Correct calculations)
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 ---- --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.611 / Virus Database: 391 - Release Date: 03/03/2004 |
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