A 10.00‐g sample containing an analyte is transferred to a 250‐mL volumetric flask and diluted to volume. When a 10.00 mL aliquot of the resulting solution is diluted to 25.00 mL it gives signal of 0.235 (arbitrary units). A second 10.00‐mL portion of the solution is spiked with 10.00 mL of a 1.00‐ppm standard solution of the analyte and diluted to 25.00 mL. The signal for the spiked sample is 0.502. (a) Calculate the weight percent (%w/w) of analyte in the original sample. (7) (b) What calibration method was used here? Explain your answer.
Chloroform is an internal standard in the determination of the pesticide DDT in a polarographic analysis in which each compound is reduced at an electrode surface. A mixture containing 0.500 mM chloroform and 0.800 mM DDT gave signals of 15.3 µA for chloroform and 10.1 µA for DDT. An unknown solution (10.0 mL) containing DDT was placed in a 100‐mL volumetric flask and 10.2 µL of chloroform (FM 119.39 g/mol, density = 1.484 g/mL) were added. After dilution to the mark with solvent, polarographic signals of 29.4 and 8.7 µA were observed for the chloroform and DDT, respectively. (a) Identify the analyte, the technique and the type of signal used. (3) (b) Find the concentration of DDT in the unknown.
What was the effect of the addition of FeCl3 to the sample solution in the dichromate titration? Explain
Calculate the percentage Fe2+ in the salt based on: a) The dichromate titration. b) The permanganate titration using the colour change end point.
The precipitate was filtered, washed free of precipitating agent, dried, and weighed, and 0.4114 g was recovered. Calculate the percentage of Hg2Cl2 in the sample.
Find the total enthalpy for rection
2C (g) + 3H2 (g) C2H6 (g)
Given the thermochemical equations.
2C(g) + 2 O2 (g) 2CO2 (g) ∆H = -786 kJ/mol
3H2 (g) + O2 (g) 3H2O (l) ∆H = -858 kJ/mol
2CO2 (g) + 3H2O (l) C2H6 (g) + O2 (g) ∆H = +1560 kJ/mol
Chalcopyrite (CuFeS2) is a principal mineral of copper. Calculate the number of
kilograms of Cu in 3.71 X 103kg of chalcopyrite.
Silver sulphide and hydrogen gas are combined to form silver solid and hydrogen
sulphide gas. 10.0 g of H2 and 125.0 g of Ag2S are used in reaction.
What quantity of Ag is produced ?
A 550 J of work is done on the refrigerant during compression. how much is the change in its internal energy when 1,000 J of heat is absorbed
. Calculate HCV and LCV of a fuel, whose composition by mass is as follows;
Carbon – 90%, Hydrogen – 90%, Sulphur – 90% and reminder being Ash