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1. 1. Explain why the molar mass of co2 is the same in the gas and solid state.

2. Estimate the no. of air molecules that enter you lungs when you inhale deeply. Assume the molar mass of air is 0.029kg snd its density at 0 degrees C and 100 kPa is 1.3 kg/m3.

For the second one I rearranged to get volume=mass/density and got 0.022. Do I need to do n=pV/RT and use p as 100,000, T as 273 and R the gas constant and estimate the voulume of your lungs?

Thanks in advance for any help
2. (Original post by alpha kenny body)
1. Explain why the molar mass of co2 is the same in the gas and solid state.

2. Estimate the no. of air molecules that enter you lungs when you inhale deeply. Assume the molar mass of air is 0.029kg snd its density at 0 degrees C and 100 kPa is 1.3 kg/m3.

For the second one I rearranged to get volume=mass/density and got 0.022. Do I need to do n=pV/RT and use p as 100,000, T as 273 and R the gas constant and estimate the voulume of your lungs?

Thanks in advance for any help
1. The molar mass of a substance is the mass of 6x10^23 molecules/atoms of the substance. Whether the element is solid or gas has no bearing on it's mass - there are still the same number of molecules/atoms so the mass is the same.

2. You can use n=pv/RT with an estimate for the volume of your lungs to work out the no. of moles of gas you breath in at 273 degrees. Then to work out the number of air molecules, just multiply by avagadro's constant (6x10^23).

However, I think the question wants you to do it an easier way: Estimate a value for the volume of your lungs (in metres cubed remember!). Then use mass=volume x density to work out the mass of the amount of air you've breathed in. The've told you that the molar mass is 0.029 so divide the mass of the air breathed in by 0.029 to find out the number of moles. Then multiply by avagradro's constant to work out the number of molecules.
3. I didn't realise there were a few ways I could do it. After you told me the easier way I also realised I could also do volume = mass/density to get volume of 1 mole and then do my estimated volume/vol of 1 mole and then x by avogadro's constant.

Thanks a lot for your help
4. Argh! I am so tired mate, maybe someone else can answer those two :P
5. For part a - the sealed cylinder, V and n are constant so P/T is constant

P1/T1 = P2/T2 ( yes temps need to be in Kelvin)

For part b) P is constant , V = constant. so nT = constant so mT = constant

so as T increases the mass in the cylinder decreases. Work out the new mass and hence the decrease.
6. Thanks a lot for your help teachercol. Much appreciated. Would you also be able to give me any pointers on the question above that? Me and my friends have all had some difficulty with how to go about that one.

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