. A sample of 4 g of cobalt isotope is produced. If the half-life of is 30 years, what will be the mass of the cobalt remaining after 90 years?

Half Life = 90/30 = 3 Half lives

Half Life = 30 years

So,

4 g Cobalt after 30 years = 4/2

=> 2 g

2 g Cobalt after next 30 years = 2/2

=> 1 g

1 g Cobalt after next 30 years = 1/2

=> 0.5 g

So, After 90 years, 0.5g of cobalt isotope will be left.

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explanation:

  1.the balanced   chemical equation is as below

cu +   2 ag(no)₃ → cu(no₃)₂   +2 ag

2.the   much silver   produced   is   50.9 g

step 1: find the   moles of cu

moles =   mass÷   molar mass

  from periodic table the molar mass of cu = 63.5 g/mol

moles is therefore = 15.00 g÷ 63.5 g/mol = 0.236   moles

step 2: use the mole ratio to determine the   moles of ag

from equation above   cu: ag   is 1: 2

therefore the moles of ag   =0.236   moles   x 2/1 =0.472   moles

step 3: find the mass   of ag

mass = moles x molar mass

from periodic table   the molar mass of ag =107.87 g/mol

mass   = 0.472   moles x 107.87 g/mol = 50.9 g

3.   the   much   silver   collected worth is   1.797 oz

  convert   50.9 g   to oz

that is   1 gram = 0.0353 oz

          50.9 grams =?   oz

by cross multiplication

={(50.9 grams x 0.0353 oz) / 1   gram}   =1.797 oz