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3 years ago

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(25 points) A certain isotope of technetium has a half-life of 8 hours. How much of a 40 gram sample will be left after 16 hours

?
A. 10 grams
B. 40 grams
C. 5 grams
D. 20 grams

1 answer:

gtnhenbr [62]3 years ago

6 0

Answer:

A) 10 grams

Explanation:

16 hours = 2 half lives

This means that the number is divided in half twice.

40/2 = 20

20/2 = 10

I hope this helps!! :)

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Step 1 : Find moles of crystal violet and NaOH.

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$Molarity = \frac{mol}{L}$

Molarity of crystal violet = $3.00 \times 10^{-3} = \frac{mol (CrystalViolet)}{L}$

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Step 2 : Find total volume of the solution

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Step 3 : Use molarity formula to find final concentrations

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Final concentration of CV = 0.0027 M

Molarity of NaOH= $\frac{mol(NaOH)}{Total Volume(L) } = \frac{5.00 \times 10^{-4}}{0.020} = 0.025 \times 10^{-3}$

NaOH is a strong base and dissociates completely as follows.

$NaOH (aq) \rightarrow Na^{+} (aq) + OH^{-} (aq)$

The mole ratio of NaOH and OH⁻ is 1:1 . Therefore the concentration of OH⁻ is same as that of NaOH.

Concentration of OH⁻ = 0.025 M

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