Question

An empty glass container has a mass of 418.634 grams. It has a mass of 419.514 grams after it has been filled with nitrogen gas at a pressure of 790 mmHg and a temperature of 15^oC. When the container is evacuated and refilled with a certain element X at a pressure of 745 mmHg and a temperature of 26^oC, it has a mass of 420.652 grams.

            Compound Y, a gaseous organic compound that consists of 88.9% carbon and 11.1 % hydrogen by mass, is placed in a stainless steel vessel ( 10.68 L) with excess oxygen gas. The vessel is placed in a constant temperature bath at 22^oC. The pressure in the vessel is 9.970 atm. In the bottom of the vessel is a container that is packed with ascarite and a desiccant. Ascarite is asbestos impregnated with sodium hydroxide; it reacts with and quantitatively absorbs carbon dioxide:

               2NaOH (s) + CO₂ (g) → Na₂CO₃(s) + H₂O(l)

            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 Ascarite nor the desiccant reacts with compound Y or oxygen. The total mass of the container with the Ascarite and the desiccant is 746.3 grams.

            The combustion of compound Y is initiated by a spark. The pressure in the container immediately rises, then begins to decrease and finally reaches a steady value of 1.51 atm.The stainless vessel is carefully opened and the mass of the container inside the vessel is found to be 878.7 grams.

            X and Y react quantitatively in a 2:1 mole ratio to form one mole of the single product, gas Z.

a)How many grams of Z will be produced if 11.0 L of X and 9.60 L of Y (each at STP) are reacted by opening a stopcock connecting the 2 sample containers?

b)What will be the total pressure in the system? Assume all reactants and products are gases. Temp = 0^oC

I have found that element x is cl2, but i think that element y is c4h6, but I'm not sure so i would appreciate the work, and i would also appreciate working on a and b in full detail. This is due tomorrow, so please help me! Thank you :)

Answer 1

P₁V₁ = n₁RT₁ => Mass of nitrogen = 419.514 - 418.634 = 0.88 gram, Moles of N2= 0.88/28

P₂V₂ = n₂RT₂ => Mass of X = 420.652 - 418.634= 2.018 gram , let n2 = moles of X

by division of these two equations

(790/745)=(0.0314/n2)(288/299)

n2 = 0.0285 moles => Molar mass of X = mass/n2 = 2.018/0.0285~70.8 gram/mol

it should be Cl₂ =X

Compound Y :

              C                                   H

%               88.1                               11.1

mole           88.1/12                           11.1/1

Relative ratio   7.34/7.34                11.1/7.34

                      = 1                          ~ 1.5

So the emprirical formula of Y = C₂H₃   => Moleculat formula = C₄H₆ = Y

so your answers are correct.

   H2C=CH-CH=CH2 +     2 Cl₂   ---------->    H2CCl-CClH-CHCl-CH2Cl (Z)

Moles          9.6/22.4                     11/22.4

                    0.47moles                0.49 mole( limiting reagnent)

Moles of Z = 1/2 (moles of X) = 0.49x(1/2)=> MAss of Z = 0.49x1/2(196)=48.118 gram

b) P_total   = n_totalRT/V

ntotal = 0.225 + 0.245 = 0.47 moles