Precipitate rules4/16/2023 Increase pressure or decrease temperature.Modern seawater has lots of dissolved ions! Examples: Ca Cl 2, Ca SO 4, MgCO 3, Na 2CO 3 *The increasing availability of ions that can tie up either Ca 2+ or CO 3 2- will lowers the effective concentration of Ca 2+ or CO 3 2- and increases solubility, making it more difficult for Ca 2+ and CO 3 2- to combine and precipitate. Lower solubility means more CaCO 3 precipitates! Note that carbon speciates in the water depending on the water pH: (At lower pressures and higher temperatures, CO 2 can escape as a gas.) When temperature is lower, more CO 2 dissolves into the water. When pressure is higher, more CO 2 dissolves into the water. Pressure × volume = amount (moles) × ideal gas constant × temperature + + + Ĭarbon dioxide + bicarbonate + carbonate + carbonic acid If we switched the values so that Ω < K - in other words, we had too much CaCO 3 - then the reaction runs forward: CaCO 3 will dissolve. Therefore, CaCO 3 will precipitate when Ω > K.Įxtra CaCO 3 stops precipitating when equilibrium is reached: So, in our example, the reaction will run backward - toward CaCO 3. To achieve equilibrium, the amount of CaCO 3 must increase, and it will increase until it reaches the number that will give us a ratio of 1:10 8.35. This means that in our example, where we have 10 products for every 1 reactant, there are too many products (Ca 2+ and CO 3 2-) compared to K c. ![]() In this example, the balance is "top heavy" compared to the equilibrium value (K c), where there are 1 products for every 10 8.35 reactants. Ω tells us how much we have relative to what we need for a saturated solution. ![]() SkepticalScience on ocean acidification (make sure you go through all of the mini-pages).CaCO 3 (s) + H 2CO 3 (aq) ⇌ Ca 2+ (aq) + 2HCO 3 - (aq)įor refreshers on chemistry concepts like Qc and Kc, see these websites:
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