Thallium-201, a radioactive isotope used to image the heart, has a half life of 3.05 days. how long would it take for a sample of thallium-201 to decay to 18% of its original activity?

= 7.55 days

Half life is the time taken by a radioactive isotope to decay by half its original amount.

To calculate the new mass or amount;

New mass = Original mass × (1/2)^n ; where n is the number of half lives.

New mass = 18%, while the original mass = 100 %, half life = 3.05 days

18 = 100 × (1/2)^n

(1/2)^n = 0.18

introducing logarithms;

n log 0.5 = log 0.18

n = log 0.18/ log 0.5

  = 2.474

But 1 half life is 3.05 days

Hence; time taken will be;

= 3.05 × 2.474

= 7.55 days

1.consider the following balanced equation and answer parts a through. show calculations for each part.  

3 ag(s) + 4 hno3(aq) → 3 agno3(aq) + no(g) + 2 h2o(l)  

a. calculate the number of moles of agno3 produced by the reaction of 3 moles of ag with excess hno3. if the number to the left of the compound represents the number of moles of the compound which are present, then 3 moles of ag react with 4 moles hno3 to produce 3 moles agno3 (aq).

so the answer to a would be 3 moles.

b. calculate the number of moles of agno3 produced by the reaction of 108 grams of ag with excess hno3.  

i'm not sure how to plug in the grams of silver into an equation using moles to find how many moles are produced.

c. calculate the number of grams of agno3 produced by the reaction of 108 grams of ag with excess hno3  

d. calculate the number of moles of no produced as a byproduct of the reaction of 108 grams of ag with excess hno3.  

e. calculate the number of grams of no produced as a byproduct starting with 108 grams of ag and excess hno3.  

explanation:

a  solution  is always transparent, light passes through with no scattering from solute particles which are molecule in size. the  solution  is homogeneous and does not settle out. a colloid is intermediate between asolution  and a  suspension. while asuspension  will separate out a colloid will not.