A Model Med Exam for CLS 231
Write your comments on the followings:
1- In complexometry, EBT should be 10-100 times less stable than the metal titrant.
So metal titrant will displace the indicator from thr metal giving good and sharp EP.
2- Volhard method is a type of an indirect titration.
Because AgNO3 is added in excess amount and the unreacted mmol of it will be determined by titrating it with another standard (KSCN).
3- Primary standard should have a high formula weight.
To avoid any weight error.
1- 1- How many grams of Na2SO4 should be weighed out to prepare 500ml of a 0.100M solution?
Weight (g)= M x V(l) x MWt(g/mol)
= 0.001 x 500/1000 x 142 (g/mol)
= 0.071 gm
2- 2- Calculate the pOH of A solution with [H+] of 4 C 10-7 M
pH= -log[4 × 10-7 ] = 6.4
pOH= 14 – 6.4 = 7.6
3- 3- Calculate the grams of analyte per gram of ppt for the following conversion:
A) Wt of P= atomic wt P / Mwt Ag3PO4
30.97 / 418.58 × 1/1 = 0.07399 g = GF
B) Wt of Bi2S3 / BaSO4
Mwt Bi2S3 /Mwt BaSO4 × 1/3 = 0.73429 g = GF
4- A 250 mL of air collected in Riyadh contains the following gases:
a) 0.000625 mL hydrogen sulfide.
b) 0.00125 mL hydrogen cynide.
Express the conc. of each gas in ppm.
a) ppm (gas) = µL solute / 1L air
Hydrogen sulfide = 0.625 /0.25
= 2.5 ppm
b) hydrogen cynide = 1.25 /0.25