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# Ideal gas equation question help! watch

1. 10 g of calcium nitrate is heated at 100kPA and a temperature of 300 degrees celcius at which temperature it fully decomposes calculate:

a) the volume of nitrogen dioxide evolved
b) total volume of oxygen evolved
c)the total gas volume of gas evolved
Equation: 2Ca(NO3)2 (s) ----> 2CaO(s) + 4NO2(g) + O2(g)

Im confused what to do when there are 2 gases involved what steps should I take, I have no idea how approach this problem.Any help would be appreciated.
2. So to help you with part (a) (part b should be the same methodology):

1) Look at the formula you have to use - in this case you know it will be PV=nRT. Look at what you already have and what you are missing. You have temperature, pressure, gas constant always given and you are trying to work out volume. So that leaves n which is moles.

2)) You know you have 10g of Calcium Nitrate and you can work out the Mr of calcium nitrate. That should immediately tell you that you can work out the number of moles it has:
Mr = 196 --> Mass = Mr.Moles --> Moles = Mass/Mr --> 10/196 = 0.05102 moles of Ca(NO3)2

3) Refer to the chemical equation given. You know you have that much moles of Calcium Nitrate being put into the reaction and so looking at the ratios you will see that NO2 is a 2:4 ratio (1:2) compared to calcium nitrate. You should then double your moles calculated before as you will have that many moles of NO2 when the reaction is complete.
2Ca(NO3)2 (s) ----> 2CaO(s) + 4NO2(g) + O2(g)

0.05102*2 = 0.10204

4) You now have moles of NO2 so you should be able to put it into the equation --> V = (nRT)/P Making sure that you correctly convert all the units.

I got an answer of 4.86 x 10-3 m3 so try to see if that is what you got. I might have miscalculated the Mr of Calcium Nitrate so do check. Part b follows the same logic but the ratio is different and that is it so you have to adjust it accordingly. Part (c) would involve you just adding part a and b together.

I hope this helps
3. (Original post by Anonymous1502)
10 g of calcium nitrate is heated at 100kPA and a temperature of 300 degrees celcius at which temperature it fully decomposes calculate:

a) the volume of nitrogen dioxide evolved
b) total volume of oxygen evolved
c)the total gas volume of gas evolved
Equation: 2Ca(NO3)2 (s) ----> 2CaO(s) + 4NO2(g) + O2(g)

Im confused what to do when there are 2 gases involved what steps should I take, I have no idea how approach this problem.Any help would be appreciated.
You find the amount of moles of calcium nitrate by doing n= mass/RFM = 10/164.1 = 0.0609 moles
Then x2 to get the amount of moles of nitrogen dioxide as the molar ratio between calcium nitrate and nitrogen dioxide is 1:2 = 0.244 moles.
Then input this into the ideal gas equation to find volume
You do the same for oxygen but the ratio between calcium nitrate and oxygen is 2:1 therefore you divide 0.0609 by 2 and input those moles into the ideal gaas equation to find the volume of oxygen.
add the 2 together to find the total volume
4. Thanks for your help guys! But how would you do this question:

Lead(IV) oxide dissolves in concentrated HCl according to the following equation:

PbO2(s) + 4HCl ---> PbCl2(s) + Cl2(g) + 2H2O(l)

Starting with 37.2 g of lead(IV) oxide calculate:
a) The volume of 12 moldm^-3 HCl needed to completely dissolve it
b)Mass of PbCl2 produced
c) The volume of chlorine produced at 298 K and 100kPa

For A I found out the moles for PbO2 by finding mr 207.2+32=239.2
Found the number of moles by doing 37.2/239.2 and multiplied the number by 4 as the ratio of HCl to PbO2 is 4:1.But then I don't knwo what to do since I don't knwo what the temperature is and I don't know how I would work it out?
5. (Original post by Anonymous1502)
Thanks for your help guys! But how would you do this question:

Lead(IV) oxide dissolves in concentrated HCl according to the following equation:

PbO2(s) + 4HCl ---> PbCl2(s) + Cl2(g) + 2H2O(l)

Starting with 37.2 g of lead(IV) oxide calculate:
a) The volume of 12 moldm^-3 HCl needed to completely dissolve it
b)Mass of PbCl2 produced
c) The volume of chlorine produced at 298 K and 100kPa

For A I found out the moles for PbO2 by finding mr 207.2+32=239.2
Found the number of moles by doing 37.2/239.2 and multiplied the number by 4 as the ratio of HCl to PbO2 is 4:1.But then I don't knwo what to do since I don't knwo what the temperature is and I don't know how I would work it out?
Here, HCl is a solution and not a gas, you should be using
volume of HCl = moles/concentration instead of the gas equation.

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