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Ivan
2 years ago
5

How long will it take for a 40.0 gram sample of I-131 (half-life = 8.4 days) to decay to 1/16 its original mass?

Chemistry
1 answer:
Shtirlitz [24]2 years ago
6 0

Answer:

42 days

Explanation:

Half life = 8.4 days

Starting mass = 40.0 g

Time = ?

Final Mass = 1/16 * 40 = 2.5 g

First Half life;

Remaining mass = 40 / 2 = 20g

Second Half life;

Remaining mass = 20 / 2 = 10g

Third Half life;

Remaining mass = 10 / 2 = 5g

Fourth Half life;

Remaining mass = 5 / 2 = 2.5g

Time = Number of half lives * Duration of half life = 5 * 8.4 = 42 days

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3 years ago
A solution containing 0.050 g of an unknown nonelectrolyte in 2.50 g of cyclohexane (Kf = 20.4 oC/m &amp; F.P. 6.6 oC) was found
ANEK [815]

Answer:

The molar mass of the unknown substance is 255g/mole

Explanation:

Freezing point depression is given by

ΔT = i · Kf · m

Where

m = molality of the solute

i = van't Hoff's factor = i for non electrolyte

Kf = 20.4 °C/m = cryoscopic constant

ΔT = Freezing point depression

Therefore ΔT = 6.6 - 5 = 1.6 °C

1.6 °C = 20.4 °C/m × 1 × m

Therefore m = 1.6/20.4 = 0.0784 m

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2.5 ×0.0784/1000 moles in 2.5 graams of cyclohexane  that is

1.96 × 10⁻⁵ moles in 2.5 grams of cyclohexane

1.96 × 10⁻⁵ moles of the substance weighs 0.050 grams

Therefore 1 Mole weighs (0.05 g)/(1.96 × 10⁻⁵ moles) = 255g/mole

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3 years ago
Zn + 2 HCl --&gt; H2 + ZnCl2 If 1.70 g of Zn are reacted, how many grams of ZnCl2 can be created? Show work and process and I wi
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Explanation:

first find the the number of moles of of zinc .

as the number of moles of zinc and ZnCl2 is same we can calculate the mass of ZnCl2.

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