Question 5: It has been estimated that the concentration of CO2 in the atmospher

Question

Question 5: It has been estimated that the concentration of CO2 in the atmosphere before the industrial revelation was about 275 ppm. If the accumulation of CO2 in the atmosphere continues, by the middle of this century, it will be probably around 600 ppm. a- Calculate the pH of rain water (neglecting the effect of any other gases) at 25 degreeC both before the industrial revelation and by the middle of this century. b- Natural rain is slightly acidic since it has an average pH of 5.6, while acid rain has a pH ranging from 4.5 to 2.1 (which is similar to lemon juice). According to the predicted concentration of CO2 in the atmosphere by 2050 (hopefully we all will be alive by that time to observe the consequences of our actions), briefly mention how often we may face to acid rains and what type of ecosystem we might have (maximum 150 word). The appended information can be helpful to answer this part of the question.

Explanation / Answer

Answer : Here first step is to calculate the molarity or Concentration of CO2

275 ppm means = 275 g per 1000 L = 0.275 g per 1 L

now molar mass of CO2 is = 44 g/mol

Hence moles in 1 L = mass / molar mass = 0.275 / 44 = 0.00625 = 6.25 * 10-3 mol

Hence molarity = 6.25 * 10^-3 M [ before industrial revolution }

Now the chemical equation is

CO2  + H2O --------------------------> H+   + HCO3-

Now assuming no other source of H+ then we get

[H+ ] = [HCO3-] ( concentrations of both are equal)

Now the equilibrium constant equation is

K a = [H+ ] 2 / [CO2] { here the value of equilibrium constant is 4.45 * 10-7]

now putting all the values and calculate the concentration of H+

4.45 *10^-7 = [H+]2 / 6.25 *10^-3

[H+ ] = 5.27 * 10-5

so Now the Ph will be equal to = - log[H+] = approx it is equal to 4.29

Hence the Ph of rain water before industrial revelation is 4.29

Now, after industrial revelation

concentration of CO2 is 600 ppm hence now again calculate molarity or concentration of CO2

600 ppm means = 600 g per 1000 L = 0.6 g per 1 L

molar mass of Co2 = 44 g/mol

so moles in 1 L = 0.6 / 44 = 0.0136 = 1.36 * 10-2 mol

hence molarity of CO2 = 1.36 * 10-2M

Now again using the same equation and same formula we get

4.45 * 10-7  = [H+]2/1.36 * 10-2

now [H+] = 7.779 * 10-5

And we know Ph = - log[H+] = 4.1

hence the after industrial revelation the PH is 4.1

Part b } Here you should write about the Harm full effects of acids rains and the effects of acids rains in marble and etc.

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