U-238 which has a long half-life is also find the ages of geological formations (rocks). Meanwhile I-131, which has much shorter half-life, is used for diagnosing thyroid disorders. What is the mass of an original 5.6 gram sample of I-131 that is still radioactive after 16.042 days?

The mass after 16.042 days : 1.4 g

Given

mass of 5.6 gram sample of I-131

time=16.042 days

Required

The mass of a sample

Solution

General formulas used in decay:  

T = duration of decay  

t 1/2 = half-life  

N₀ = the number of initial radioactive atoms  

Nt = the number of radioactive atoms left after decaying during T time  

Half-life of I-131 = 8 days

Input the value :

answer: c.

explanation:

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