You start with 420 mg of isotope which has half life of 20 days. How many mg will be left after 40 days

105 mg

Explanation:

The following data were obtained from the question:

Original amount (N₀) = 420 mg

Half life (t½) =20 days

Time (t) = 40 days

Amount remaining (N) =..?

Next, we shall determine the rate constant K, for the disintegration.

This can be obtained as follow:

Half life (t½) =20 days

Rate constant (K) =?

K = 0.693/ t½

K = 0.693/20

K = 0.03465 /day

Finally, we shall determine the amount remaining after 40 days as follow:

Original amount (N₀) = 420 mg

Rate constant (K) = 0.03465 /day

Time (t) = 40 days

Amount remaining (N) =..?

Log(N₀/N) = kt/2.3

Log (420/N) = (0.03465 x 40)/2.3

Log (420/N) = 1.386/2.3

Log (420/N) = 0.6026

420/N = antilog (0.6026)

420/N = 4

Cross multiply

420 = N x 4

Divide both side by 4

N = 420/4

N = 105 mg

Therefore, the amount remaining after 40 days is 105 mg.

0

explanation:

488479

rvmoo+478)9.68

in 1783 cavendish was working with his hydrogen gas and found that when he burned it and condensed the vapor it was water. this was very significant since it disproved the greek theory of elements completely since water was not a simple substance but the product of two gases. it was lavoisier who hearing of the experiment gave cavendish's gas the name hydrogen ("water-producer") and added that hydrogen burned by combining with oxygen and that water was a hydrogen-oxygen combination.

explanation: