Consider the following statements and write V if it is TRUE and F if it is FALSE
ID: 1024260 • Letter: C
Question
Consider the following statements and write V if it is TRUE and F if it is FALSE. (Answer and explain)
() For a 2nd order reaction, the half life time (t ½) depends on the concentration and is equal to 1am, the first hour of reaction the concentration does not decrease and the second time decreases half.
() To 1st order reaction the half life (t ½) k depends only.
() The nuclear activity of a sample is the number of nuclear disintegrations occurring in a certain time interval divided by the interval length, and is measured in Bq. () The nuclide produced by the decay of Po-211 is the Pb-207 and decay of Na-24 is the In-23
. () The equilibrium constant for an aqueous substance concentration of 0.1 mol.L-1 and lower percentage of dissociation than 2%, whose pH 2.9 is measured in the laboratory is 5,4x10-5 .
The correct sequence of the statements above is:
A) F, V, V, F, F.
B) F, V, V, V, F.
C) F, V, F, V, F.
D) V, F, F, V, V.
Explanation / Answer
1. The first statement is false(F). Bacause for 2nd order reaction half-life, t1/2 = 1 / k[A]o. Also in 2nd order reaction the concentration of reactant decreases with time whether it is first hour or second hour.
2. The 2nd statement is true(V), Because for first order reaction half-life, t1/2 = 0.693 / k. Hence half-life, t1/2 only depends on k.
3. The 3rd statement is also true(V). Because the nuclear activity of a sample is defined as the number of nuclear disintigrations occuring in a certain time interval divided by total interval length, or else we can say that the number of disintigrations in a particular time interval. Also Bacquerel(Bq) is the unit of nuclear activity.
4. The 4th statement is false(F). Because, although the alpha-decay of 84Po-211 produces 82Pb-207, the beta - decay of 11Na24 produces 12Mg-24.
5: The 5th statement is also false(F)
Given Ka = 5.4x10-5
Concentration, C = 0.1 M
Since the percentage dissociation is very small, the pH of the weak acid can be calculated as
[H+] = square root (Ka x C) = square root (5.4x10-5 x 0.1) = 2.32x10-3 M
=> pH = - log[H+] = - log(2.32x10-3 M) = 2.63
However the given pH is 2.9
Hence the proper sequence should be (A): F, V, V, F, F