The last one on that list would be your answer
Answer:
The Ka value used for the buffer system is :- Ka2 = pKa2 = 7.2
pH = 7.1
Explanation:
The buffer system given in the question is :-
and
The reaction taking place is:-
The Ka value used for the buffer system is :- Ka2 = pKa2 = 7.2
The pH can be calculated as:-
pH = 7.2 + log 0.40/0.50 = 7.1
Equation for Half life :
A = a(0.5)^(t/h)
A is current amount, "a" is initial amount, h is halflife, t is time
5 = 40(0.5)^(t/1.3x10^9)
5/40 = (0.5)^(t/1.3x10^9)
take the log of both sides , power rule
Log(5/40) = (t/1.3x10^9) * Log(0.5)
(1.3x10^9) * Log(5/40) / Log(0.5) = t
3.9x10^9 years = t
And if you think about what a half life is, the time it take for the amount to reduce to half.
40/2 = 20
20/2 = 10
10/2 = 5
It went through 3 half-lifes
3 * 1.3x10^9 = 3.9x10^9 years