Luna asked in Science & MathematicsChemistry · 4 months ago

The Half-life element X is 15 min. What weight of X was original present in a sample of 40 grams is left after 1 hour? ?

AP Chem Question: 

Choice answers are:

A) 160 grams

B) 320 grams

C) 640 grams 

D) 1280 grams

6 Answers

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  • 4 months ago
    Favourite answer

    1 hour = 4 half-lives

    40 g = mₒ × (1/2)⁴

    Original mass, mₒ = 40 × 2⁴ g = 640 g

    The answer: C) 640 g

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  • Anonymous
    4 months ago

    4 half lives, 1/16 of the original amount.

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  • Jim
    Lv 7
    4 months ago

    A = A₀ (1/2)^(t/h)

    40 = A₀ (1/2)^(60m/15m)

    40 = A₀ (1/2)^(4) = A₀ (1/16

    A₀ = 40 *16/1 = 640g ANswer C.

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  • 4 months ago

    N = No e^(-0.693*T/Tk)

    40 = No * e^(-0.693 * 60/15) = No * 0.0625

    No = 640 g

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  • 4 months ago

    Answer 'C'

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  • 4 months ago

    15 minutes ... half is left.

    30 minutes ... 1/4 is left

    45 minutes ... 1/8 is left

    60 minutes ... (can you figure this part ?)

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