A sterling silver bracelet, which is 92.5% silver by mass, has a volume of 25.6

ID: 1021840 • Letter: A

Question

A sterling silver bracelet, which is 92.5% silver by mass, has a volume of 25.6 cm3 and a density of 10.2 g/cm3.

Part A What is the mass, in kilograms, of the bracelet?

Part B Determine the number of protons and neutrons in the following isotope of silver:
107/47Ag

Part C Determine the number of protons and neutrons in the following isotope of silver:
109/47 Ag

Part E Ag112 decays by beta emission. Write the balanced nuclear equation for the decay of Ag112.

Part F A 64.0Ci sample of Ag112 decays to 8.00 Ci in 9.3 h. What is the half-life of Ag112?

1) mass = volume x density

= 25.6 cm3 x 10.2 g/cm3 x (92.5/100)

= 241.5 g

= 0.24 kg

2) number of protons = 47 , number of neutrons = 107 - 47 = 60

3) number of protons = 47 , number of netrons = 109 - 47 = 62

4) the beta emission of Ag-112 is given by

112/47 Ag --------------> 112 / 48 Ag + 0/-1 e

5) from the equation k = 2.303/t log( A0/At )

k = 2.303/ ( 9.3 x 3600 s) log ( 64 .0 / 8.0 )

k = 6.23 x 10^-5 /s

and from t1/2 = 0.693 / k = 0.693 / (6.23 x 10^-5 /s )

= 1.11 x 10^4 s

= 3.08 hr

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