For which of the following activities might you want to hire a chemist?
Answer: D. testing a rock sample for gold content
Which of the following procedures involves a physical change in one of the substances?
Answer: C. separating a salt solution by evaporating the water
Answer:
0.0468 g.
Explanation:
- The decay of radioactive elements obeys first-order kinetics.
- For a first-order reaction: k = ln2/(t1/2) = 0.693/(t1/2).
Where, k is the rate constant of the reaction.
t1/2 is the half-life time of the reaction (t1/2 = 1620 years).
∴ k = ln2/(t1/2) = 0.693/(1620 years) = 4.28 x 10⁻⁴ year⁻¹.
- For first-order reaction: <em>kt = lna/(a-x).</em>
where, k is the rate constant of the reaction (k = 4.28 x 10⁻⁴ year⁻¹).
t is the time of the reaction (t = t1/2 x 8 = 1620 years x 8 = 12960 year).
a is the initial concentration (a = 12.0 g).
(a-x) is the remaining concentration.
∴ kt = lna/(a-x)
(4.28 x 10⁻⁴ year⁻¹)(12960 year) = ln(12)/(a-x).
5.54688 = ln(12)/(a-x).
Taking e for the both sides:
256.34 = (12)/(a-x).
<em>∴ (a-x) = 12/256.34 = 0.0468 g.</em>
B
. They are large and occur at shallow depths near the where the plates diverge.
Answer:
All atoms of the same element have always have the same amount of protons.
Explanation:
Atoms of the same element have always have the same amount of protons but not always the same electrons and neutrons. If an atom gains or loses one of its valance electrons, the electrons on the outermost shell, then it becomes ionized. Also not all atoms of the same element have the same amount of neutron. This is called an isotope. A good example would be Carbon 13. Normally, Carbon atoms have an atomic mass of 12 AMU or 12 atomic mass units. However, Carbon atoms have an atomic mass of 13 AMU, consisting of 7 neutrons instead of 6 neutrons. So the only thing that all atoms of the same element have in common is the amount of protons.
Answer:
B
Explanation:
so that way they can hide away from the predators
