What Are the Solutions to These Chemistry Problems?

[almirza]

1)
10 cm^3 of a gas G were mixed with 100 cm^3 (an axcess) of oxygen in a sealed container at 20 C and one atmosphere pressure . The gas was then ignited electrically and burned completely in the oxygen. After the reaction the volume of the gas mixture measured at the the same temperature & pressure , was found to be 105 cm^3. Which of the following was G?
A CH4
B H2
c CO
D C2H4

and how?
2)
10 cm^3 of a gaseous hydrocarbon needed 30 cm^3 of oxygen for complete combustion and 20 cm^3 of CO2 were produced . What is the molecular formula of the hydrocarbon and how?
A CH4
B C2H2
C C2H4
D C2H6
3)
In the thermit reaction :
2Al + Cr2O3 produce 2Cr+ Al2O3
Calculate the percentage yield when 180 g of chromium are obtained from a reaction between 100 g of aluminium and 400 g of chromium.
4)
A sample of hydrated compound was analysed and found to contain 2.10g of cobalt , 1.14g of sulphur , 2.28g of oxygen and 4.50g of water. Calculate the emperical formula .
5)
A 10.0g of a compound contained 3.91g of carbon , 0.87g of hydrogen and the reminder is oxygen. Calculate the emperical formula of the compound.

[ these questions are not difficult but there are some small problem make me not sure ]

 

[GCT]

https://www.physicsforums.com/showthread.php?t=94384

 

[Blueshift5]

1) Based on the given information, the gas G is most likely methane (CH4). This is because methane is a common gas that can be burned in oxygen, and it produces carbon dioxide and water vapor as byproducts. The balanced chemical equation for the reaction is:

CH4 + 2O2 → CO2 + 2H2O

Since the volume of the gas mixture increased by 5 cm^3 after the reaction, it is likely that the methane completely burned and produced 5 cm^3 of carbon dioxide and 10 cm^3 of water vapor.

2) The molecular formula of the hydrocarbon in question is likely C2H4 (ethylene). This is because it requires 30 cm^3 of oxygen for complete combustion, and produces 20 cm^3 of carbon dioxide. The balanced chemical equation for the reaction is:

C2H4 + 3O2 → 2CO2 + 2H2O

This means that for every 2 molecules of ethylene, 3 molecules of oxygen are needed, and 2 molecules of carbon dioxide are produced. This matches the given information, making C2H4 the most likely molecular formula.

3) The percentage yield can be calculated by dividing the actual yield (180 g) by the theoretical yield. The theoretical yield is the amount of chromium that would be produced if the reaction went to completion, which can be calculated by using the balanced chemical equation:

2Al + Cr2O3 → 2Cr + Al2O3

From the equation, we can see that 2 moles of aluminum react with 1 mole of chromium (Cr2O3). Therefore, the theoretical yield of chromium is:

(100 g Al) / (2 mol Al) x (1 mol Cr) x (52 g Cr) = 2600 g Cr

The percentage yield is then:

(180 g Cr) / (2600 g Cr) x 100% = 6.9%

4) To determine the empirical formula, we first need to calculate the molar masses of each element present in the compound. The molar mass of cobalt (Co) is 58.93 g/mol, sulfur (S) is 32.07 g/mol, oxygen (O) is 16.00 g/mol, and water (H2O) is 18.02 g/mol.

Next, we need to calculate the number of moles of