Question

pH of which of the following salts remains same
for 2M and 6M concentration of the solution ?
(1) CH3COONa
(2) C6H5NH3Cl
(3) HCOONH4
(4) KCN
Please give correct answer with proper explanation. ​

Answer 1

Ideal Gas equation gives: PV = nRT

since density (ρ)=mV,

then

PV=mMRT or PM=mVRT=ρRT

since density ρ=mV,

then

PV=mMRT or PM=mVRT=ρRT

For two different gases, we have two different expression as:

P1M1=ρ1RT1 −−−−(i)

P2M2=ρ2RT2 −−−−(ii)Dividing equation (i) by (ii),

we get P1M1P2M2=ρ1RT1 ρ2RT2P1M1P2M2=ρ1R2T2 2ρ1RT2 [since, density are in ratio 1:2 and temperature are in ratio 2:1]

P1M1P2M2=1P1P2=M2M1P1M1=ρ1RT1 ----i

P2M2=ρ2RT2 ----ii

Dividing equation i by ii,

we get

P1M1P2M2=ρ1RT1 ρ2RT2P1M1P2M2=ρ1R2T2 2ρ1RT2 [since, density are in ratio 1:2 and temperature are in ratio 2:1]

P1M1P2M2=1P1P2=M2M1

Hence, ratio of their pressure is inverse of the ratio of their molecular masses