To work out the actual pH of the created buffer, you need to measure the pK_a of carbonateâs conjugate acid. Describe the experimental set-up required to measure this pK_a value, including the piece of glassware needed for each of the two necessary solutions. Make sure to measure pK_a, not pK_b!

From your measurement above, you have found the pK_a to be 10.3. âAcid-freeâ paper should have a pH around between 8.7 and 10.2. What pH is the buffer in your paper pulp if you add 0.5 mM calcium carbonate to pulp that started with 0.35 mM acid (pH=3.37)? Hint: Find the concentration of carbonate and its conjugate acid after the reaction.

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Day 1. Synthesis and characterization of HA and CHA. Preparation of ceramics. Prepare two solutions, 100 mL each: (1) 0.5 M Ca2+ solution (from Ca(NO3)2Â·4H2O) with pH adjusted to 11 using 1 M NaOH; (2) 0.3 M solution of PO4 3- ions (from Na2HPO4). For the synthesis of CHA add the carbonate source (NaHCO3) to the phosphate solution such that the PO4 3- : CO3 2- ratio is 5:1 or 2:1. Dropwise add the phosphate and carbonate solutions over the course of 10 minutes to the calcium solution. Heat and mix the solution to 80 Â°C for 1 hour adjusting the pH to 11 if needed by adding 1 M NaOH. Cool it down and vacuum filter your precipitate, wash three times with DI water. Dry the powder in the oven and calculate your yield. Use some of the dry powder to press a pellet. This pellet will be annealed at ~1000 Â°C overnight to fabricate dense ceramic material, which will be used later in the SBF test. Submit some of the sample to your TA for XRD measurements. If time permits, perform FTIR measurements of your sample and compare it to bovine CHA.

Day 2. Preparation of SBF.6 Thoroughly clean 1000 mL glass beaker, try to avoid heavily scratched glassware. 1) Add 960 mL of deionized water and dissolve 6.5456 g of NaCl, stir vigorously at RT for 5 min 2) Dissolve 2.2682 g of NaHCO3 and stir vigorously at RT for 5 min 3) Dissolve 0.373 g of KCl and stir vigorously at RT for 5 min 4) Dissolve 0.1419 g of Na2HPO4 and stir vigorously at RT for 5 min 5) Heat the solution to 36.5-37 Â°C 6) Dissolve 0.3049 g of MgCl2Â·6H2O and stir vigorously for 5 min 7) Add 9 mL of 1 M HCl solution (use a pipette and add it slowly) and stir vigorously for 5 min 8) In small portions add 0.3675 g of CaCl2Â·2H2O and stir vigorously for 5 min 9) Add 0.071 g of Na2SO4 and stir vigorously for 5 min 10) In small portions add 6.057 g of Tris [=(CH2OH)3CNH2]. Upon adding Tris, the solution should become turbid; keep stirring. 11) Insert the pH electrode into the solution, which should be at around 37Â°C until now 12) Add 30 mL of 1 M HCl slowly in 5 mL portions, by using a pipette, your addition plan is 5 + 5 + 5 + 5 + 5 + 5 mL = 30 mL (with the addition of each 5 mL portion of 1 M HCl, pH will gradually drop towards 7.4) 13) Keep stirring and be careful when adding the last â5 mL portionâ of 1 M HCl, add this 5 mL portion quite slowly (i.e., drop by drop) while watching the pH meter reading 14) You can easily adjust the pH at 7.4 (at 36.5 or 37Â°C), pH=7.38, 7.37, 7.41 or 7.39 are also OK 15) Measure the total volume of the transparent solution, if it is not exactly equal to 1000 mL, you must add deionized water to complete the volume to 1000 mL Table 2. Order and amounts of reagents for 1000 mL of SBF.

# Reagent Amount 1 NaCl 6.5456 g 2 NaHCO3 2.2682 g 3 KCl 0.373 g 4 Na2HPO4 0.1419 g 5 MgCl2Â·6H2O 0.3049 g 6 1.0M HCl 9 mL 7 CaCl2Â·2H2O 0.3675 g 8 Na2SO4 0.071 g 9 Tris 6.057 g 10 1.0M HCl 30 mL

Prepare a water bath heated to ~37 Â°C. Put the SBF solution into a 25 mL glass vial and heat it to 36.5 Â°C on a water bath. Place a pellet of ceramic material such that the entire sample is submerged in the SBF, seal the container and leave it at 36.5 Â°C until the next lab period.

question: Not all of the carbonate ions used in the reaction actually incorporate in the final structure of CHA. Propose a characterization method to quantitatively study amount of carbonate in your CHA samples (for instance, carbonate to phosphate ratio, which might be different from what you have in your solution at the beginning). Propose a method to estimate the ratio between A- and B- type carbonates and explain how/why this method can distinguish the A- and B- type carbonate substitution.

In the synthesis of a diester experiment (Chemiluminescence) using 4-nitrophenol (procedure shown below), explain the significance / role of the reagents used:

-- What does triethylamine do?

-- What does oxalyl chloride do? Why must it be added slowly?

-- Why is a calcium carbonate drying tube used?

-- Why is cold acetone used to wash the solid product?