Technetium-104 has a half-life of 18.0 minutes. How much of a 165.0 g sample remains after 36.0 minutes?

41.25g

Explanation:

Given parameters:

Half-life of Technetium - 104  = 18minutes

Mass = 165g

Unknown:

Mass of sample remaining after 36minutes = ?

Solution:

The half-life of a radioactive element is the time taken for half of the element to decay;

Now;

                Start           First half life              Second half-life

Time          0                      18min                        36min

 Mass       165g                 82.5g                        41.25g

a. the law of proportion states the combination of 2 atoms in a specific ratio to produce multiple compounds such as the given statement of question ‘1st compound contains 88.8 % cu ’ indicates 88.8 g of cu is present along with 11.2 g oxygen in 100 g of compound whereas the statement ‘2st compound contains 79.9 % cu ’ indicates 79.9 g of cu is present along with 20.1 g oxygen in 100 g of compound

1st compound contains 88.8 g cu

for cu

m = 63 g /mol

atomic % = 88.8 /63 = 1.42

for o

m = 16 g /mol

atomic % = 11.2 /16 = 0.7

b. the emperical formula of 1st compound is

cu1.4o0.7

cu2o