Carbonate Chemistry

I have a lab experiment in which I have a slurry of wood pulp at a pH of 4.0; I'm asked to use sodium carbonate to raise the pH of the slurry to pH 5.5. I then press the wood slurry to de-water and place it in an oven until it is bone dry. I then take the wood sample out of the oven and place it in a bath of water to determine how much water the wood absorbs. Why would the addition of sodium carbonate potentially cause more water to be absorbed into the wood specimen? And, if I wanted to continue to use a carbonate chemistry for pH adjustment (because it has other beneficial properties), is calcium carbonate less hydrophylic than sodium carbonate? Is there another carbonate chemistry c... click for more

Aluminum sulfate as a flocculant?

In a lab experiment, a solution of weak acids in water exhibit a pH of 3.7; the solution is known to have a known quantity of dissolved solids in solution. Paper makers alum (aluminum sulfate = Al2(SO4)3) is supposed to be used to coagulate/flocculate the dissolved solids in order to precipitate those solids. In the course of the experiment, it appeared that the pH at which the best flocculation occurred using alum was between a pH 4.7 to 5.0 ---- seemingly any higher or lower pH resulted in less preciptable solids?? Why would this be? Interestingly, much of the literature I could find regarding alum does in fact suggest that aluminum sulfate exhibits optimal flocculation at pH 4.7... click for more

Balancing Chemical Equations and Understanding Reaction

I have a 1 liter solution of unknown weak acid in water of which the pH is 4.0. I have 1 known compound that will be added to this solution --- that being alum (aluminum sulfate = Al2(SO4)3. The objective is to add either sodium carbonate or calcium carbonate to the solution to adjust the pH to 5.0. The desired output reaction is to produce aluminum hydroxide (Al(OH)3) solids but the aluminum solids are supposed to form at a pH in which those solids would exhibit the lowest level of solubility!!!!! Also, to the extent that any sodium or calcium preciptate occurs, the desired result is once again to have the most hydrophobic of sodium or calcium precipitate ---- I suspect that is calcium??? ... click for more

Carbonate chemistry --- Impact of solubility on ability to increase pH?

How does the solubility of a particular reactant affect its ability to raise pH. I am particularly interested in the difference between sodium carbonate and calcium carbonate. Calcium carbonate is much much less soluble than sodium carbonate. However, does the solubility of the carbonate matter when adjusting pH from say 4.0 to 5.0? Please help so that I can understand the relationship between a reactants solubility and its ability to affect pH?

Aluminum Hydroxide Formation

Could you please help me better understand the formation of aluminum hydroxide --- for instance: Again, lets assume we have a generally weak acid solution to which we add aluminum sulfate. The objective is to precipitate aluminum hydroxide per the following reaction which I believe to be correct. Al2(SO4)3 + HCO3- = 2Al(OH)3 + SO4-- I do not want Al2(SO4)3 + H2O = 2Al(OH)3 + H2SO4 I want to ensure that the reaction prefers or goes in the direction of the first equation. However, pH has something to do as to which reaction is favored ---- if pH is too low I believe the second equation is favored. If pH is closer to neutral then I believe the first equation is favored. But wh... click for more