10.2 Use the following information to identify element A and compound B; then an

Question

10.2 Use the following information to identify element A and compound B; then answer questions a and b. An empty glass container has a mass of has a mass of 659.452 g after it has 658.572 g. It been filled with nitrogen gas at a pressure of 790. torr and a temperature of 15 oC. When the container is evacuated and refilled with a certain element (A) a pressure of torr and a temperature of 26 C, it 745. has a mass of 660.59 g. Compound B, a gaseous organic compound that consists of 85.6% carbon and 14.4% The vessel is placed in a constant-temperature bath at 22°C. The pressure in the vessel is 11.98 atm. In the bottom of the vessel is a container that is packed with Ascarite and a desiccant. rite is asbestos impregnated with sodium hydroxide, it quantitatively absorbs carbon dioxide 2NaOH (s) CO2-Na2CO, (s) H2O() The desiccant is anhydrous magnesium perchlorate, which quantitatively absorbs the water produced by the combustion reaction as well as the water produced by the above reaction. Neither the desiccant nor the Ascarite reacts either with compound B or oxygen. The total mass of the container with the Ascarite and desiccant is 765.3g.

Explanation / Answer

Part 1-

Step1-Calculate the moles of N2

Mass of N2 = 659.452g - 658.572g = 0.880g

Now calculate mole N2

n = 0.880g x (1 mole / 28.01g) = 0.03142 moles N2

Step2-Calculate the volume of the container-

Assume the gases are ideal

PV = n RT

V = n RT/P

R = 0.0821 L atm /moleK

T = 15°C = 288K

P = 790 torr x (1atm / 760 torr) = 1.039 atm.

V = (0.03142moles) x (0.08206 Latm/moleK) x (288K) / (1.039atm)

V = 0.7143 L

Step3-Calculate the molar mass element

PV = nRT

n = mass / mw

PV = (mass/mw) RT

mw = mass RT / PV

mw = (660.59g - 658.572g) x (0.08206 L atm/moleK) x (299K) / [(745torr x 1atm/760torr) x (0.7143L)]

mw = 70.7 g/mole

The element with molar mass 70.7 g/mole being a gas at that temp and pressure is chlorine Cl2.

Part 2 -

85.6% C and 14.4%H (given)

Assume mass of compound is 100g

Moles C = 85.6g x (1 mole / 12.01g) = 7.13 moles

Moles H = 14.4g x (1 mole / 1.008g) = 14.29

Divide both by the smallest and get this empirical formula CH2

Now the reactions may be-

CnH2n + 3n/2 O2 ---> n CO2 + n H2O   reaction (i)

n CO2 + 2n NaOH ---> n Na2CO3 + n H2O

1 CnH2n ---> 1n CO2 + 2n H2O + other stuff and all of that CO2 and H2O get absorbed

So mass H2O + CO2 from the first reaction = 846.7g - 765.3g = 81.4g

The second reaction doesn't matter provided that nothing left as a gas.

Since the ratio of CO2 to H2O is 1:1 in reaction (i)

Fraction CO2 = 44.01g / (44.01g + 18.02g) = 0.7095

Mass CO2 absorbed = 81.4g absorbed x (0.7095g CO2 / 1g absorbed) = 57.75g

By converting mass of CO2 to moles CO2, moles CO2 to moles O2 via the balanced equation

57.75g CO2 x (1 mole CO2 / 44.01g CO2) = 1.312 moles CO2

1.312 moles CO2 x (1.5n O2 / n CO2) = 1.968 moles O2

n = PV/RT = (6.02 atm) x (10.68L) / [(0.08206Latm/moleK) x (295K)] = 2.656 moles O2

Moles O2 initial = moles O2 consumed + moles O2 remaining = 1.968 + 2.656 = 4.624

n = PV/RT = (11.98 atm) x (10.68L) / [(0.08206 Latm/moleK) x (295K)] = 5.285 moles total

Moles B = 5.285 - 4.624 = 0.661

1.312 = 0.661xn

n = 2 meaning gas B is C2H4

Part 3-

1 C2H4 + 1 Cl2 ---> 1 C2H4Cl2

H2C = CH2 -----> ClH2C - CH2Cl

For gases at the same temp and pressure, the coefficients of the balanced equation are in mole ratios and also in volume ratios

V1 / n1 = V2 / n2

V1 / V2 = n1 / n2

From the balanced equation, 1 L C2H4 reacts with 1 L Cl2

10.0 L Cl2 x (1 L C2H4/ 1 L Cl2) = 10.0 L C2H4

There is only 8.6 L C2H4, so C2H4 is limiting reagent.

Mass C2H4Cl2 is

8.6 L C2H4 x (1 L C2H4Cl2 / 1 L C2H4) x (1 mole C2H4Cl2 / 22.4 L) x (167.7g C2H4Cl2/ mole C2H4Cl2) = 64.4g C2H4Cl2

Part4-

At STP 1,2-dichloroethane is a liquid.

n = PV/RT = (1 atm) x (1.40L) / [(0.08206Latm/moleK) x (273K)] = 0.06249 moles Cl2

18.60 L container that is evacuated, then placed 64.6g C2H2Cl2 + 0.06249 moles Cl2 in it then adjusted the temperature to 273K

The total pressure will be the partial pressure of Cl2 + partial pressure of C2H4Cl2.

PCl2 = nRT/V = (0.06249 moles) x (0.08206Latm/moleK) x (273K) / (18.60L) = 0.0753 atm

And PC2H4Cl2 will go by the clausius chaperon equation..

ln(P1/P2) = (dHvap / R) x (1/T2 - 1/T1)

where

P1 = PC2H4Cl2

P2 = 1 atm (P at normal bp)

dHvap = 33910 J/mole

R = 8.314 J/moleK

T2 = normal bp at 1 atm = 84°C = 357K

T1 = 273K P1 = PC2H4Cl2

T2 = normal bp at 1 atm = 84°C = 357K

T1 = 273K

P1 = [exp(33910 J/mole / 8.314 J/moleK) x (1/357 - 1/273) ] x 1 atm = 0.02974 atm

n = (0.02974 atm) x (18.60L) / [(0.08206 Latm/moleK) x (273K)]

n = 0.02469 moles C2H4Cl2 = 2.44g

Total pressure = 0.0753 atm + .0297 atm = 0.105 atm

P1 = [exp(33910 J/mole / 8.314 J/moleK) x (1/357 - 1/273) ] x 1 atm = 0.02974 atm

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