1. Copper is often added to paint for ocean-going ships and boats to discourage

Question

1. Copper is often added to paint for ocean-going ships and boats to discourage the growth of marine organisms on their hulls. Unfortunately, the copper dissolves into the water and is toxic to the marine life in harbors where these boats are docked. When copper(II) ions reach a concentration of 9.0 micrograms/liter, the growth of some marine life slows. How many copper ions are found in a liter of water containing 5.8 micrograms of Cu2+ per liter?

2. Cobalt-60 has a half-life of 5.26 years. If 3.84 g of 60Co were allowed to decay, how many grams would be left after

(a) one half life?
(b) two half lives?
(c) four half lives?

(d) ten half lives?

3. Anthropologists have found bones whose age suggests that the human line may have emerged in Africa as much as 4 million years ago. If wood or charcoal were found with such bones, would C-14 dating be useful in dating the bones?

______ half-lives would pass in 4 million?

Explanation / Answer

1. Molar mass of Cu = 63.5 g/mol

number of ions of Cu2+ = mass/molar mass ) Avogadro number = 5.8 x 10-6/ 63.5) 6

.022 x 1023 = 0.55 x 1017

2. after 1 half life 1.92 g

after 2 hal life = 0.96 g

after 4 half lide = 0.24'g

after 10 half life = 0.00375 g

3. Half life of carbon 14 is 5,730 years

Number of half life = 4 million/5730 = 698 half lves

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