Physical Chemistry Answers

The capacity of elimination of a dye in aqueous solution by adsorption on activated carbon was studied. Four
solutions with different dye concentration were prepared and 40 mL from each of them were put in contact
with activated carbon. Once equilibrium was attained, a aliquot was taken from each of the flasks and their
absorbances were measured at 665 nm. The following table shows the measured absorbances, the initial dye
concentrations (expressed in mmoles/L) and the exact quantity of activated carbon contained in each flask:
carbon masss(g): 0,133; 0,102; 0,100; 0,105
10^3Co9(mM): 50; 100; 160; 190
A: 0,007; 0,026; 0,106; 0,177

The molar extinction coefficient of the dye at 665 nm was previously determined and a value of 16,33 mM
cm_swas obtained.

Obtain the adsorption constant from a linear fit of the C/q vs. C. Do all calculations in mM scale.

In an adsorption experiment of methylene blue (C16H18N3-Cl-S, PM=319,85 g/mol) onto activated carbon, the linear

fitting y=10,095-x + 0,0181 was obtained when C/q versus C was represented, being C the equilibrium concentration in mmol/L
and q the adsorbed amount in mmol/g.

Estimate the specific surface of the activated carbon knowing that the cross sectional area of the dye is 110 A^2

To obtain the distribution constant of iodine between water and carbon tetrachloride (CCI,), two
solutions were placed together to attain the equilibrium: 50 mL of a saturated iodine solution in CCI,
+ 150 mL of water.

After 1 hour shaking at 25°C, the equilibrium was achieved. Two portions of each solution were
sampled and titrated with sodium thiosulphate. 15 mL of the organic phase needed 17,0 mL of
thiosulphate, and 50 mL of the aqueous solution needed 22 mL of a thiosulphate solution 5 times
diluted. Obtain the distribution coefficient.

A potentiometric titration of HCl 0,00735M is done with NaOH 0,01127 M in the burette. Both
solutions have the same ionic strength, 0,4 M. The analysis of the titration using the Gran plot yields
a straight line for the acid side with a slope equal to -76480. The basic side line has a slope of
116092. Nernst slope value is 59,16 mV. Obtain the stoichiometric pK of water at that ionic strength.

Calculate ∆H, w, q and ∆U for heating 1.00 mol of argon from 100 K to 300 K at a constant volume of 30.6 L.

A buffered solution of 25 mL of an acid-base indicator is prepared by mixing 5mL of a stock solution of indicator 2,10x10^-4 M + 2,5 mL of Na2CO3 0,1 M + 10mL of NaHCO3 0,2 M
The stoichiometric equilibrium constant of carbonic acid are 4,47x10^-7 and 4,68x10^-11
Calculate the pH of this solution.

Calculate the average molecular speed of O_2 at 300 K in m/s.

During electrolysis of aq. NaCl solution for 6 hours, 11.2 litres of Cl2 gas at STP is evolved at anode. The current
in amperes passing through the cell during electrolysis is

When the following oxidation-reduction equation representing a reaction that takes
place in BASIC solution is correctly balanced using the smallest possible whole number
coefficients, the coefficient before the Al is:
Al + NO2
- = Al(OH)4
- + NH3

A halogen gas mixture contained in a 8.0L cylinder holds 25.0g of Cl2 and 10.0g of F2. The temperature of the tank is 25 degree Celsius, what is the total pressure in the cylinder, in atmosphere?