Calculate the ph of a 0.200 m ch3nh3cl solution. kb for methylamine, ch3nh2, is 3.7 Ã 10-4.

Answer : The value of pH of the solution is, 5.6

Explanation : Given,

The dissociation constant for methylamine =

First we have to calculate the value of .

The equilibrium chemical reaction will be:

Initial conc.      0.2                            0             0

At eqm.         (0.2-x)                          x             x

The expression for dissociation constant of acid is:

By solving the term, we get the value of 'x'.

x = 2.3 × 10⁻⁶

x = -2.3 × 10⁻⁶

We are neglecting negative value of x.

Thus, the value of x = 2.3 × 10⁻⁶

Now we have to calculate the value of pH.

Therefore, the value of pH of the solution is, 5.6

part 1: the half-life of the element is 22 years.

part 2: it will take 132.02 year for the sample to decay from 308.0 g to 4.8125 g.

explanation:

part 1: there are two ways to determine the half life time.

first way: the half life time can be determined directly from its definition as it is the time required for the sample to decay to its half concentration.

from the data the initial concentration was 45.0 g and decayed to its half value (22.5 g) in 22.0 years.

second way: the radio active decay is considered first order reaction so we can use the laws of first order reactions.

k = (1/t) ln (a/a-x), where k is the rate constant of the reaction,

t is the time of the reaction

a is the initial concentration of the reactant

a-x is the remaining concentration at time (t)

a = 45.0 g the initial concentration at t = 0 year.

at t = 22 year, a-x = 22.5 g

then k = (1/22 year) ln (45.0 g/ 22.5 g) = 0.0315 year-1.

the half-life time (t1/2) = ln 2/ k = 0.693/ k =0.693/ 0.0315 = 22 years.

part 2:

using the same law k = (1/t) ln (a/a-x),

using the given data; a = 308.0 g and a-x = 4.8125 g and the calculated k from the part 1 (k = 0.0315 year-1)

t = (1/k) ln (a/a-x) = (1/0.0315) ln (308.0/ 4.8125) = 132.02 years

i believe it is 40–40–20%

explanation: