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horrorfan [7]
2 years ago
12

An unknown radioactive substance has a half-life of 3.20 hours . If 16.5 g of the substance is currently present, what mass A0 w

as present 8.00 hours ago
Chemistry
1 answer:
guajiro [1.7K]2 years ago
6 0

Answer:

the amount present 8 hours ago is Ao = 93.338 g

Explanation:

the radioactive decay is given by

A = Ao * 2^(- t/T)

where T = half-life of the substance , t= time , A= amount of substance at time t , Ao= amount of substance at time 0

therefore at t=8 hours , A=16.5 gr

Ao = A*2^(t/T) = 16.5 g * 2^(8 hours/3.20 hours) = 93.338 g

Ao = 93.338 g

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san4es73 [151]

The number of moles of the magnesium (mg) is 0.00067 mol.

The number of moles of hydrogen gas is 0.0008 mol.

The volume of 1 more hydrogen gas (mL) at STP is 22.4 L.

<h3>Number of moles of the magnesium (mg)</h3>

The number of moles of the magnesium (mg) is calculated as follows;

number of moles = reacting mass / molar mass

molar mass of magnesium (mg) = 24 g/mol

number of moles = 0.016 g / 24 g/mol = 0.00067 mol.

<h3>Number of moles of hydrogen gas</h3>

PV = nRT

n = PV/RT

Apply Boyle's law to determine the change in volume.

P1V1 = P2V2

V2 = (P1V1)/P2

V2 = (101.39 x 146)/(116.54)

V2 = 127.02 mL

Now determine the number of moles using the following value of ideal constant.

R = 8.314 LkPa/mol.K

n = (15.15 kPa x 0.127 L)/(8.314 x 290.95)

n = 0.0008

<h3>Volume of 1 mole of hydrogen gas at STP</h3>

V = nRT/P

V = (1 x 8.314 x 273) / (101.325)

V = 22.4 L

Learn more about number of moles here: brainly.com/question/13314627

#SPJ1

7 0
1 year ago
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