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Elan Coil [88]
2 years ago
5

You are using a Geiger counter to measure the activity of a radioactive substance over the course of several minutes. If the rea

ding of 400. counts has diminished to 100. counts after 90.3 minutes , what is the half-life of this substance? Express your answer with the appropriate units. View Available Hint(s) t1/2 t 1 / 2 t_1/2 = nothing
Chemistry
1 answer:
taurus [48]2 years ago
8 0

Answer:

t₁/₂ = 45.1 min

Explanation:

The  radioactive decay equation is given by

N/N₀ = e^-kt  where N = counts after time t

                                 N₀ = counts initially

                                 k = decay constant

                                 t=  time elapsed

The question is what´s the half-life of this substance, and we can solve it once we have k from the expression above since

                                 t₁/₂ = 0.693/k

which is derived from  that equation, but for the case    N/N₀ is 0.5

Lets calculate k and  t₁/₂ :

N/N₀ = e^-kt      (taking ln in the two sides of the equation)

ln (N/N₀) =  ln e^-kt   = -kt   ⇒ k = -ln(N/N₀)/t

k = -ln(100/400)/90.3 min = 0.01535 min⁻¹

 t₁/₂ = 0.693/k  = 0.693/0.01535 min⁻¹  = 45.1 min

We can check this answer since the time in the question is the double of this  half-life and the data shows the material has decayed by a fourth: two half-lives.

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4 0
3 years ago
I need help with balancing equations I'm doing homework and idk what to do here can you give me the answers please lol
amm1812

It's pretty easy to balance equations! Basically you want to make sure that the number of each compound is equal on both sides of the arrow.

For example number one is

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A 3 in front of H2SO4 because there's a subscript of 3 on the right side.

Then a 3 in front of H2 because of the previous step.

Then add a 2 in front of Fe because of the 2 subscript in Fe2(SO4)3

Then add a 1 in front of Fe2(SO4)3 because you already have an equal number of each element.

<u>2</u>Fe + <u>3</u>H2SO4 -> <u>1</u>Fe2(SO4)3 + <u>3</u>H2

I hope this explanation helps! You should really do your homework because practice is everything when it comes to chemistry. You'll need to know how to do it for exams.  

3 0
3 years ago
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1 year ago
A hydrate is compound that included water molecules within its crystal structure. During an experiment to determine the percent
stellarik [79]

Answer:

The percent by mass of water in this crystal is:

  • <u>21.4%</u>

Explanation:

This exercise can be easily solved using a simple rule of three where the initial weight of the hydrated crystal (6,235 g) is taken into account as 100% of the mass, and the percentage to which the mass of 4.90 g corresponds (after getting warm). First, the values and unknown variable are established:

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And the value of the variable X is found:

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  • X = approximately 78.6%.

The calculated value is not yet the percentage of the water, since the water after heating the glass has evaporated, therefore, the remaining percentage must be taken, which can be calculated by subtraction:

  • Water percentage = Total percentage - Percentage after heating.
  • <u>Water percentage = 100% - 78.6% = 21.4%</u>
4 0
3 years ago
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