Chemistry, 27.07.2019 21:30 angel10999

If the mass of a radioactive substance is 8 grams and it has a half-life of 4 hours, how much mass remains after 8 hours?

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The sample will lose half of its mass after 4 hours. The half life.
82=4
The sample will lose half of the remaining four after another half life.
42=2 Hope this helps! :)

Answer from: neptunesx

2 grams will be remaining.

Explanation: Half life is the time in which the amount of radioactive substance remains half.

For example if half life of a radioactive substance is 3 hours and we have 16 grams of it then in two hours, 8 grams will be remaining. In next two hours, 4 grams will be remaining. Similarly, in next two hours, 2 grams and further in next two hours 1 gram of the substance will be remaining.

For the given problem, the half life of the radioactive substance is 4 hours. It means the initial amount of this substance will remain half in 4 hours.

Originally we have 8 grams of the radioactive substance. In first 4 hours, 4 grams of the substance will be remaining. Now, in next 4 hours that is in total 8 hours, 2 grams of the substance will be remaining.

These problems could also be solved mathematically using the formula:

$\frac{N}{N_0}=(0.5)^n$

where, N_0 is the initial amount of the substance, N is remaining amount and n is the number of half lives.

number of half lives(n) = $\frac{time}{half life}$

From given information, time is 8 hours and half life is 4 hours.

So, n = $\frac{8}{4}$ = 2

Initial amount is given as 8 grams and it asks to calculate the remaining amount. Let's plug in the values in the equation:

$\frac{N}{8}=(0.5)^2$

$\frac{N}{8}$ = 0.25

N = 8(0.25)

N = 2

So, from both ways 2 grams of the radioactive substance will be remaining after 8 hours.

Answer from: Quest

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.

Answer from: Quest

all eukaryotic cell have mitochondria : )

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If the mass of a radioactive substance is 8 grams and it has a half-life of 4 hours, how much mass r...

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