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Snowcat [4.5K]
3 years ago
6

Cobalt-60 is a strong gamma emitter that has a half- life of 5.26 yr. The co balt-60 in a radiotherapy unit must be replaced whe

n its radioactivity falls to 75% of the original sample. If an original sample was purchased in June 2016, when will it be necessary to replace the cobalt-60?
Chemistry
1 answer:
Alenkasestr [34]3 years ago
3 0

<u>Answer:</u> The sample of Cobalt-60 isotope must be replaced in January 2027

<u>Explanation:</u>

The equation used to calculate rate constant from given half life for first order kinetics:

t_{1/2}=\frac{0.693}{k}

where,

t_{1/2} = half life of the reaction = 5.26 years

Putting values in above equation, we get:

k=\frac{0.693}{5.26yrs}=0.132yrs^{-1}

Rate law expression for first order kinetics is given by the equation:

k=\frac{2.303}{t}\log\frac{[A_o]}{[A]}

where,

k = rate constant = 0.132yr^{-1}

t = time taken for decay process = ? yr

[A_o] = initial amount of the sample = 100 grams

[A] = amount left after decay process =  (100 - 75) = 25 grams

Putting values in above equation, we get:

0.132=\frac{2.303}{t}\log\frac{100}{25}\\\\t=10.5yrs

The original sample was purchased in June 2016

As, June is the 6th month of the year, which means the time period will be 2016+\frac{6}{12}=2016.5

Adding the time in the original time period, we get:

2016.5+10.5=2027

Hence, the sample of Cobalt-60 isotope must be replaced in January 2027

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6.0 mol NaOH reacts with
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<h3>How to calculate number of moles?</h3>

The number of moles of a substance can be calculated stoichiometrically as follows:

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1 year ago
A drum used to transport crude oil has a volume of 162 L. How many grams of water, as steam, are required to fill the drum at 1.
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Answer:

114.48g

Explanation:

Step 1:

Data obtained from the question:

Volume (V) = 162 L

Pressure (P) = 1.20 atm

Temperature = 100°C = 100°C+ 273 = 373K

Number of mole (n) of H2O =?

Recall:

Gas constant (R) = 0.082atm.L/Kmol

Step 2:

Determination of the number of mole of H2O i.e steam.

Using the ideal gas equation, the number of mole of H2O can be obtained as follow:

PV = nRT

1.2x 162 = n x 0.082 x 373

Divide both side by 0.082 x 373

n = (1.2x 162) /(0.082 x 373)

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Determination of mass of H2O i.e steam:

This is illustrated below:

Molar Mass of H2O = (2x1) + 16 = 2 + 16 = 18g/mol

Number of mole H2O = 6.36 moles

Mass of H2O =?

Mass = number of mole x molar Mass

Mass of H2O = 6.36 x 18

Mass of H2O = 114.48g

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