Iodine-131 is a beta emitter used as a tracer in radio immunoassays in biological systems. It follows first order kinetics. The half-life if iodine-131 is 8.04 days. If you start with 8.0 grams of iodine-131, how many grams would remain at 39 days

The amount of Iodine-131 remain after 39 days is 0.278 grams

Explanation:

The equation used to calculate rate constant from given half life for first order kinetics:

where,

= half life of the reaction = 8.04 days

Putting values in above equation, we get:

Rate law expression for first order kinetics is given by the equation:

where,

k = rate constant =

t = time taken for decay process = 39 days

= initial amount of the sample = 8.0 grams

[A] = amount left after decay process = ?

Putting values in above equation, we get:

Hence, the amount of Iodine-131 remain after 39 days is 0.278 grams

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g