This question is testing to see how well you understand the "half-life" of radioactive elements, and how well you can manipulate and dance around them. This is not an easy question.
The idea is that the "half-life" is a certain amount of time. It's the time it takes for 'half' of the atoms in any sample of that particular unstable element to 'decay' ... their nuclei die, fall apart, and turn into nuclei of other elements.
Look over the table. There are 4,500 atoms of this radioactive substance when the time is 12,000 seconds, and there are 2,250 atoms of it left when the time is ' y ' seconds. Gosh ... 2,250 is exactly half of 4,500 ! So the length of time from 12,000 seconds until ' y ' is the half life of this substance ! But how can we find the length of the half-life ? ? ?
Maybe we can figure it out from other information in the table !
Here's what I found:
Do you see the time when there were 3,600 atoms of it ?
That's 20,000 seconds.
... After one half-life, there were 1,800 atoms left.
... After another half-life, there were 900 atoms left.
... After another half-life, there were 450 atoms left.
==> 450 is in the table ! That's at 95,000 seconds.
So the length of time from 20,000 seconds until 95,000 seconds
is three half-lifes.
The length of time is (95,000 - 20,000) = 75,000 sec
3 half lifes = 75,000 sec
Divide each side by 3 : 1 half life = 25,000 seconds
There it is ! THAT's the number we need. We can answer the question now.
==> 2,250 atoms is half of 4,500 atoms.
==> ' y ' is one half-life later than 12,000 seconds
==> ' y ' = 12,000 + 25,000
y = 37,000 seconds .
Check:
Look how nicely 37,000sec fits in between 20,000 and 60,000 in the table.
As I said earlier, this is not the simplest half-life problem I've seen.
You really have to know what you're doing on this one. You can't
bluff through it.
Answer:
The concentration of the HNO3 solution is 0.150 M
Explanation:
<u>Step 1:</u> Data given
Volume of the unknown HNO3 sample = 0.120 L
Volume of the 0.200 M Ba(OH)2 = 45.1 mL
<u>Step 2:</u> The balanced equation
2HNO3 + Ba(OH)2 ⟶ Ba(NO3)2 + 2H2O
<u>Step 3:</u> Calculate moles Ba(OH)2
moles Ba(OH)2 = molarity * volume
moles Ba(OH)2 = 0.200 M * 0.0451 L
moles Ba(OH)2 = 0.00902 moles
<u>Step 4:</u> Calculate moles of HNO3
For 1 mole of Ba(OH)2 we need 2 moles of HNO3
For 0.00902 moles of Ba(OH)2 we need 2*0.00902 = 0.01804 moles
<u>Step 5</u>: Calculate molarity of HNO3
molarity = moles / volume
molarity = 0.01804 / 0.120 L
Molarity = 0.150 M HNO3
The concentration of the HNO3 solution is 0.150 M
The following are the statements, which indicates that the fossil record suggests about evolution on Earth:
1. Humans have only recently existed on Earth.
2. The organisms originally lived only in Earth's water.
3. The plants did not have flowers when dinosaurs existed.
The fossil remains have been discovered in the rocks of all the ages. The simplest organisms fossils are witnessed in the oldest rocks, and the fossils of more composite species are found in the newest rocks. This supports the theory of evolution suggested by Darwin, according to which the simple life forms slowly gets evolved into more composite ones.
You should be checking your gas appliances every year, it should always be a qualified technician.
Answer:
SO… The larger wire looses heat energy faster, however the smaller wire decreases temperature faster. ... Their surface area is much larger in proportion to their body mass and they lose heat through their skin when it is cold and they gain heat through their skin when it is hot much faster than an adult does.
Explanation:
