59.25 seconds
After 1 half-life: 16*(1/2) = 8 g remains
After 2 half-lives: 8*(1/2) = 4g remains
After 3 half-lvies: 4*(1/2) = 2g remains
After 4 half-lives: 2*(1/2) = 1g remains
So after 4 half-lves you have 1 gram of Na25 left. This is also the amount remaining after 237 seconds. Since 4 half-lives have elapsed over 237 seconds, you can divide 237 seconds by 4 to find the half-life of Na25 is 59.25 seconds.
You can also figure it out using the rate of decay formula:
At = Ao*e-kt
where Ao is the initial amount, At is the amount left after some time t. k is the decay constant which is k = ln 2 / t1/2 where t1/2 is the half-life.
In this case Ao = 16g, At = 1g, t=237 sec
Substitute in the formula to solve for k, then take the answer for k and use it in the other formula to solve for the half-life (t1/2):
1 = 16*e-237k
ln (1/16) = ln (e-237k)
-2.7726 = -237k
k = -2.7726/-237 = 0.011699 sec-1
t1/2 = ln 2/k = 0.693147/0.011699 sec-1
t1/2 = 59.25 sec
True
The answer depends on 3240 WHAT: seconds, days, years?
a sample is a sample sized piece given... a sample size is the amount given in one sample
An experimental sample is an experiment that is just a sample of what you are looking for.
sample is a noun and sampling is TO sample(verb)
2
1/32
1.5% remains after 43.2 seconds.
After 1.6 seconds, 0.6 g astatine-218 remains unchanged. This amount is reduced by half to 0.3 g at 3.2 seconds. It is halved again at 4.8 seconds to 0.15 g, and halved once more to 0.075 g unchanged after a total of 6.4 seconds.
Density is an intensive quantity which means it is independent of size. This can be seen from the definition of density. Density = mass/volume So if the sample size increases than so does the mass, but the density remains unchanged.
halflife
Yes, the mass of a sample of water remains unchanged when it expands. This is because only its density and volume vary with temperature. As the temperature increases, two dependent changes occur: the volume of the water increases and the density decreases. These two changes happen in correlation with each other such that the mass remains exactly the same. A second way of thinking about this problem is on a molecule scale. When heating water (composed of many H2O molecules) the number of the molecules in your sample doesn't change, nor does the mass of each molecule. Therefore there is no reason your sample's mass should change (unless you lose some water, which can be prevented by using a sealed container).
An eighth remains.
It tells what fraction of a radioactive sample remains after a certain length of time.
A sample of 187 rhenium decays to 187-omium with halflife of 41.6 billion years. If all 188 osmium are normalized isotopes.
Thorium-234 has a half-life of 24.1 days. How much of a 100-g sample of thorium-234 will be unchanged after 48.2 days?
The fraction that remains is 1/8.