A806.3 ng sample of an unknown radioactive substance was placed in storage and its mass measured periodically. after 47 days the amount of radioactive substance had decreased to 100.8 ng. how many half-lives of the unknown radioactive substance have occurred?

1. 1 mole of anything contains 6.022x10^23 pieces  

d  

2. a  

3. c, number  

5. 1.24x10^24atoms / 6.022x10^23atoms/mole = 2moles h2 atoms  

6. fe2br3 mass = 2moles x mass fe + 3 moles x mass br  

molar mass = grams / number of moles = g/mole  

to find moles = g / molar mass  

to find mass = g = molar mass / moles

the temperature of the gas, in k, not celsius.