[INHWC]

Hi, I just need some help to get started. This was supposed to be a group project but my two partners bailed on me. I don't want the answers, all I need is some help with what equations to use etc. The problem is as follows:

An empty glass container has a mass of 658.572 g. It has a mass of 659.452 g after it has been filled with nitrogen gas at a pressure of 790. torr and a temperature of 15?C. When the container is evacuated and refilled with a certain element (A) at a pressure of 745 torr and a temperature of 26?C it has mass of 660.59 g.

Compound B, a gaseous organic compound that consists of 85.6% carbon and 14.4% hydrogen by mass, is placed in a stainless steel vessel (10.68L) with excess oxygen gas. 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. Ascarite is asbestos impregnated with sodium hydroxide; it quantitatively absorbs carbon dioxide:

2NaOH (s) + CO2 (g) ? Na2CO3 (s) + H20 (l)

The desiccant is anhydrous magnesium perchlorate, which quantitatively absorbs the water produces by the combustion reaction as well as the water produced by the above reaction. Neither the Ascarite nor the desiccant reacts with compound B or oxygen. The total mass of the container with the Ascarite and desiccant is 765.3 g.

The combustion reaction of compound B is initiated by a spark. The pressure immediately rises, then begins to decrease, and finally reaches a steady value of 6.02 atm. The stainless steel vessel is carefully opened, and the mass of the container inside the vessel is found to be 846.7 g.

I know this is a long and difficult problem but it counts as a big part my grade, so some help would be greatly appriciated.

[Yggdrasil]

What do you have so far?  What part of the problem are giving you problems specifically?

[INHWC]

Sorry I haven't responded but my computer decides to work one day and not the next.

I actually don't know where to start. I'm probably just dumb but what is exactly am I looking for to find Element A (its mass, volume or what?)
The same thing goes for Compound B. I appreciate all the help I can get as you see, I'm not good at Chemistry.

[Yggdrasil]

A good starting point for gas problems is always the ideal gas law:  PV=nRT.  Keep this in mind as it will be of great use in solving the problem.

An empty glass container has a mass of 658.572 g. It has a mass of 659.452 g after it has been filled with nitrogen gas at a pressure of 790. torr and a temperature of 15?C.

From the change in mass, you can calculate the mass of nitrogen in the container.  Since nitrogen gas has a molecular weight of 28.0g/mol, you can calculate the number of moles of nitrogen in the container (n).  Since you can calculate n, and P and T are given (and R is a constant), you have all the information you need to calculate the volume of the container (V).

When the container is evacuated and refilled with a certain element (A) at a pressure of 745 torr and a temperature of 26?C it has mass of 660.59 g.

Since you know the volume of the container and P and T are given, you can now calculate the number of moles of A (n).  The change in mass gives the mass of A.  Divide the mass of A by the number of moles of A to get the molecular weight of A, which can be used to identify A (keep in mind that A is an element).


I'm not going to go through how to do part B step by step yet, but I'll give you a general strategy.  From the composition of compound B given in the problem, you can calculate an empirical forumula for your compound.  Use this empirical formula to write a balanced chemical reaction and figure out the ratio of moles of water and moles of carbon dioxide produced by the combusion of B.  The change in mass of the ascarite/dessicant container is equal to the mass of carbon dioxide and water produced.  Using the ratio calculated above, you can calculate the number of moles of water and number moles of carbon dioxide produced.  From these two values and your balanced chemical reaction you can figure out how much oxygen gas was used up.  By using the ideal gas law on the vessel before and after the reaction, you can figure out the number of moles of B you started with and use that to calculate the number of empirical formula units are in your molecular formula.

[AWK]

From this part

An empty glass container has a mass of 658.572 g. It has a mass of 659.452 g after it has been filled with nitrogen gas at a pressure of 790. torr and a temperature of 15?C. When the container is evacuated and refilled with a certain element (A) at a pressure of 745 torr and a temperature of 26?C it has mass of 660.59 g.

you can calculate the volume of the glass container, then molecular mass of element A (it mot neccesary should be monaotonic. Finally, from a periodic table you can fit element to its atomic or molecular mass.

From this part

Compound B, a gaseous organic compound that consists of 85.6% carbon and 14.4% hydrogen by mass, is placed in a stainless steel vessel (10.68L) with excess oxygen gas. The vessel is placed in a constant-temperature bath at 22?C. The pressure in the vessel is 11.98 atm. 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. Ascarite is asbestos impregnated with sodium hydroxide; it quantitatively absorbs carbon dioxide:

2NaOH (s) + CO2 (g) ? Na2CO3 (s) + H20 (l)

The desiccant is anhydrous magnesium perchlorate, which quantitatively absorbs the water produces by the combustion reaction as well as the water produced by the above reaction. Neither the Ascarite nor the desiccant reacts with compound B or oxygen. The total mass of the container with the Ascarite and desiccant is 765.3 g.

The combustion reaction of compound B is initiated by a spark. The pressure immediately rises, then begins to decrease, and finally reaches a steady value of 6.02 atm. The stainless steel vessel is carefully opened, and the mass of the container inside the vessel is found to be 846.7 g.

You can calculate
1. empirical formula of compound B (from mass percentage)
2. moles of compound B from volume of stainless vessel, temperature and  difference in pressure  after combustion.
3. Having know sum of mass CO2 and H2O (from mass of vessel after and before the combustion) and empirical formula you can split them to CO2 and H2O, then to masses of C and H.
4.Finally from masses of C and H and moles of B you can find a molecular formula of B

[Donaldson Tan]

An empty glass container has a mass of 658.572 g. It has a mass of 659.452 g after it has been filled with nitrogen gas at a pressure of 790. torr and a temperature of 15?C. When the container is evacuated and refilled with a certain element (A) at a pressure of 745 torr and a temperature of 26?C it has mass of 660.59 g.

Compound B, a gaseous organic compound that consists of 85.6% carbon and 14.4% hydrogen by mass, is placed in a stainless steel vessel (10.68L) with excess oxygen gas. 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. Ascarite is asbestos impregnated with sodium hydroxide; it quantitatively absorbs carbon dioxide:

2NaOH (s) + CO2 (g) ? Na2CO3 (s) + H20 (l)

The desiccant is anhydrous magnesium perchlorate, which quantitatively absorbs the water produces by the combustion reaction as well as the water produced by the above reaction. Neither the Ascarite nor the desiccant reacts with compound B or oxygen. The total mass of the container with the Ascarite and desiccant is 765.3 g.

The combustion reaction of compound B is initiated by a spark. The pressure immediately rises, then begins to decrease, and finally reaches a steady value of 6.02 atm. The stainless steel vessel is carefully opened, and the mass of the container inside the vessel is found to be 846.7 g.

INHWC, I cannot see the question bit in your post at all. Your post essentially contains 4 paragraphs of description. It never state the aim of the project, ie. what are we supposed to evaluate? Yggdrasl and AWK have pointed out the possible mass balances you can obtained from the description, but I don't how how helpful these balances are if there is no criteria to evaluate these mass balances.

[INHWC]

So far I calculated Element A to be Arsenic(hopefully got it right)
As for compound B i got the Empirical formula to be CH2 but after that i'm having trouble with what to do next.

(oh and Geodome, I basically have to identify Element A and Compound B and then react them to form gas C)

(Edit)
The balanced chemical reaction I got was 2CH2+3O2--->2CO2+2H2O, ratio 1:1, 0.925 mol of CO2, 2.259mol of H20  After that i'm lost

[Donaldson Tan]

As for compound B i got the Empirical formula to be CH2 but after that i'm having trouble with what to do next

The emperical formula for B (ie. CH₂) suggests B is either ethene (C2H4) or propene (C3H6).

C2H4 + 3 O2 -> 2 CO2 + 2 H2O

2 C3H6 + 9 O2 -> 6 CO2 +  6 H2O

If gas B is ethene, then the mole ratio of carbon dioxide in dessiscant to gas B inside the container is 2:1
If gas B is propene, then the mole ratio of carbon dioxide in dessiscant to gas B inside the container is 6:2 = 3:1

[Yggdrasil]

If you calculate the ratio of carbon dioxide to water to be 1 to 1, then shouldn't the reaction produce equal moles of carbon dioxide and water.  Clearly 0.925 mol is not equal to 2.259 moles, so you need to redo this part.  Basically, you have 846.7g-765.3g = 81.4g of a mixture of water and carbon dioxide.  You know that the mole ratio of carbon dioxide to water is 1, so you can find the number of moles of carbon dioxide and the number of moles of water in the mixture.

From these numbers of moles and your balanced chemical reaction, you can calculate the amount of oxygen gas which was used up in the reaction.  Also, from the final temperature, pressure, and volume of the container, you know the amount of oxygen gas which remains after the reaction.  Therefore, you can use these two numbers to find the initial number of moles of oxygen gas in the container.

Now, from the initial temp, pressure, and volume, you can find the total number of gas molesules in the container initially.  Since the initial number of moles = initial number of B and initial number of oxygen molecules, you can find the initial number of molecules of B.  Using some logic and your chemical equation, you should be able to figure out the correct formula for B from the number of molecules of B which reacted and the number of molecules of water and carbon dioxide produced.

[Donaldson Tan]

(1) C2H4 + 3 O2 -> 2 CO2 + 2 H2O

(2) 2 C3H6 + 9 O2 -> 6 CO2 +  6 H2O

If gas B is ethene, then the mole ratio of carbon dioxide in dessiscant to gas B inside the container is 2:1
If gas B is propene, then the mole ratio of carbon dioxide in dessiscant to gas B inside the container is 6:2 = 3:1

Since we cannot directly determine the number of moles of B, we must modify this method.

Fortunately, we can find the change in number of moles of gas in the container after combustion.

Initially, before combustion, the total amount of moles of gas (B + O₂) N_initial can be calculated using the perfect gas equation. Initially, the gas mixture occupies 10.68L under a pressure of 11.98atm at 22C, so N_initial = PV/RT = (11.98*1.013E5)(10.68E-3)/(8.314)(273+22) = 5.2845moles

After combustion, the steady-state pressure is 6.02atm and the temperature is 22C too. Hence,
N_final = PV/RT = (6.02*1.013E5)(10.68E-3)/(8.314)(273+22) = 2.6555moles

Moles of Gas Consumed = N_initial - N_final = 2.629 moles

Equation (1) suggests the molar ratio of gas consumed (O2 & B) to Carbon Dioxide produced is (1+3):2 = 2:1 if B is ethene.

Equation (2) suggests the molar ratio of gas consumed (O2 & B) to Carbon Dioxide produced is (9+2):6 = 11:6 of B is propene.

[INHWC]

I got the numbers you got Geodome, just rounded differently but I don't know what to do with them but
Since 2CH2+3O2--->2CO2+2H2O . I'm gonna go with Ethene C2H4 (Since C2H4+3O2--->2CO2+2H2O still works)

I just want to make sure though, that Element (A) is Arsenic.

[Donaldson Tan]

This is the quantitative proof of the identity of B

The emperical formula for B (ie. CH₂) suggests B is either ethene (C2H4) or propene (C3H6).

(1) C2H4 + 3 O2 -> 2 CO2 + 2 H2O

(2) 2 C3H6 + 9 O2 -> 6 CO2 +  6 H2O

Since Moles of Gas Consumed = 2.629 moles then

According to reaction (1),
the extent of reaction (xi₁) is 2.629/(1+3) = 0.65725 moles
Hence, the mass of combustion product = 2*xi₁*(M_CO2 + M_H2O) = 81.499g.

According to reaction (2),
the extent of reaction (xi₂) = 2.629/11,
Hence, the mass of combustion product = 6*xi₂*(M_CO2 + M_H2O) = 88.908g

Our mass balance from the difference in mass of the container before and after combustion reveals that:
mass of combustion product (CO2 + H2O) = 846.7 - 765.3 = 81.4g.

The mass balance result is in agreement with reaction (1), so gas B must be ethene.

[Donaldson Tan]

M_i refers to the molar mass of Component i