Chemistry, 18.08.2019 04:10 mochoa4

Initially, a particular sample has a total mass of 200 grams and contains 128 x 1010 radioactive nuclei. these radioactive nuclei have a half life of 1 hour. (a) after 3 hours, how many of these radioactive nuclei remain in the sample (that is, how many have not yet experienced a radioactive decay)

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Answer from: goodperson8449

Explanation:

Formula to calculate how many particles are left is as follows.

N = $N_{0} (\frac{1}{2})^{l}$

where, $N_{0}$ = number of initial particles

l = number of half lives

As it is given that number of initial particles is $128 \times 10^{10}$ and number of half-lives is 3.

Hence, putting the given values into the above equation as follows.

N = $N_{0} (\frac{1}{2})^{l}$

= $128 \times 10^{10}(\frac{1}{2})^{3}$

= $16 \times 10^{10}$

or, $1.6 \times 10^{11}$

Thus, we can conclude that $1.6 \times 10^{11}$ particles of radioactive nuclei remain in the given sample.

In five hours we've gone through 5 half lives so the answer is:

particles

Answer from: Quest

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1

0.44 / 0.09 = 4.8

mgco3-5h2o"

Answer from: Quest

Mass is the amount of matter in an object. weight is the measurement of the pull of gravity on an object. say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165) now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon. however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant. in conclusion it is possible for your weight to change as your mass remains constant.

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