Answer:
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Explanation:
It would take 147 hours for 320 g of the sample to decay to 2.5 grams from the information provided.
Radioactivity refers to the decay of a nucleus leading to the spontaneous emission of radiation. The half life of a radioactive nucleus refers to the time required for the nucleus to decay to half of its initial amount.
Looking at the table, we can see that the initial mass of radioactive material present is 186 grams, within 21 hours, the radioactive substance decayed to half of its initial mass (93 g). Hence, the half life is 21 hours.
Using the formula;
k = 0.693/t1/2
k = 0.693/21 hours = 0.033 hr-1
Using;
N=Noe^-kt
N = mass of radioactive sample at time t
No = mass of radioactive sample initially present
k = decay constant
t = time taken
Substituting values;
2.5/320= e^- 0.033 t
0.0078 = e^- 0.033 t
ln (0.0078) = 0.033 t
t = ln (0.0078)/-0.033
t = 147 hours
Learn more: brainly.com/question/6111443
Answer: 17.2 g
Explanation:
To calculate the moles :
The balanced chemical equation is:
According to stoichiometry :
4 moles of 
produce = 4 moles of 
Thus 0.085 moles of will require=
of
Mass of 
Thus 17.2 g of will be produced form 20.0 g of HgS.
We shall find the molar mass first.
Ca5(PO4)3(OH) = (40 * 5) + 3 (31 + 4(16)) + 16 + 1 = 200 + 285 + 17 = 485 + 17 = 502.
Percent of Calcium = 200/ 502 * 100 = 39.8%
Percent of Phosphorus = 91/502 * 100 = 18.1%
Percent of Hydrogen = 1/502 * 100 = 0.19%
Percent of Oxygen = 100 - (39.8 + 18.1 + 0.19) = 41.91%
