Phosphate standards used to generate the calibration curve are usually made by f
ID: 1001352 • Letter: P
Question
Phosphate standards used to generate the calibration curve are usually made by first preparing a stock solution of known concentration, then diluting it to the required concentration. First prepare a stock solution that is 1.00 Times 10^-2 M in phosphate ion. How many g of Na_3 PO_4 would you add to a 250 mL volumetric flask to prepare this solution? Mass Na_3 PO_4: What is this concentration in ppm of phosphate? (That is, as PO_4^3-, not Na_3PO_4). PO_4^3- concentration: What volume of this ppm solution would you dilute with water into a 1.000 L volumetric flask to make a solution of 10.0 ppm? This much of the work will be done for you by the laboratory assistant. You will be given a stock solution of 10.0 ppm phosphate to use in calibrating your phosphate assay. To preserve the ammonium molybdate reagent, you will create the calibrating standards by doing a serial dilution, using an aliquot of each diluted solution to create the next dilution. After adding 1 mL of ammonium molybdate reagent and 2 drops of stannous chloride to 25 mL of the 10.0 ppm solution to develop the color, use a 20 mL aliquot to dilute with 5 mL of water to make 25 mL of a solution of 8.0 ppm. Using the dilution equation: V_1 Times Conc_1 = V_2 Times Conc_2 and rearranging: 20mL = 25mA 8 ppm/10 ppm To create 25 mL of a 6.0 ppm solution, what volume of the 8.0 ppm solution and what volume of water should be mixed? To create 25 mL of a 4.0 ppm solution, what volume of the 6.0 ppm solution and what volume of water should be mixed? To create 25 mL of a 2.0 ppm solution, what volume of the 4.0 ppm solution and what volume of water should be mixed?Explanation / Answer
Molecular weight of Na3PO4= 164
Molarity = 1*10-2 moles/L
1 L= 1000 ml contains 1*10-2 moles
250ml contains 250*1*10-2/1000 =0.0025 moles
Mass of Na3PO4= moles* Molecular weight= 0.0025*164=0.41gms
Na3PO4-à 3Na+ PO4-3
1*10-2 Na3Po4- --à 1*10-2 PO4-3
1*10-2 moles/L of solution =1*10-2 moles of Po4-3/1000ml =1*10-5 moles/ml
1*10-5*95gm/ml =0.00095 gm/ml =950ppm
950*V1= 1*10
V1= 10/950 L= 0.0105L
25*6= 8*V
V= 150/8=18.75 ml
25*4= 6*V
V= 100/6= 16.66 ml
25*2=4*V
V = 12.5 ml