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ExtremeBDS [4]
3 years ago
6

The radioisotope sodium-24 is used to determine the levels of electrolytes in the body. A 16-μg sample of sodium-24 decays to 2.

0 μg in 45 h. What is the half-life, in hours, of sodium-24?
Chemistry
1 answer:
mario62 [17]3 years ago
8 0

Answer:

t = 15 hours

Explanation:

To get this, we need to write the general expression for the mass or concentration in life decay which is the following:

A = Ao * e^(-kt)   (1)

K is a constant decay and depends of the half life. The expression is:

k = ln2 / t₁/₂   (2)

In this question, we have the innitial mass and the final mass, and the time required to get that mass. So, with these data, we first solve for the constant k, and then, use this value to get the half life. In other words, we solve for k in (1) and then, solve for half life in (2):

2 = 16 * e(-45k)

2/16 = e(-45k)

0.125 = e(-45k)

ln(0.125) = -45k

k = -ln(0.125)/45

k = 0.0462 h⁻¹

Now that we have k, let's calculate half life:

t₁/₂ = ln2/k

t₁/₂ = ln2 / 0.0462

t₁/₂ = 15 h

This is the half life of sodium-24

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A gas used to extinguish fires is composed of 75 % CO2 and 25 % N2. It is stored in a 5 m3 tank at 300 kPa and 25 °C. What is th
tatyana61 [14]

Answer : The partial pressure of the CO_2 in the tank in psia is, 32.6 psia.

Explanation :

As we are given 75 % CO_2 and 25 % N_2 in terms of volume.

First we have to calculate the moles of CO_2 and N_2.

\text{Moles of }CO_2=\frac{\text{Volume of }CO_2}{\text{Volume at STP}}=\frac{75}{22.4}=3.35mole

\text{Moles of }N_2=\frac{\text{Volume of }N_2}{\text{Volume at STP}}=\frac{25}{22.4}=1.12mole

Now we have to calculate the mole fraction of CO_2.

\text{Mole fraction of }CO_2=\frac{\text{Moles of }CO_2}{\text{Moles of }CO_2+\text{Moles of }N_2}

\text{Mole fraction of }CO_2=\frac{3.35}{3.35+1.12}=0.75

Now we have to calculate the partial pressure of the CO_2 gas.

\text{Partial pressure of }CO_2=\text{Mole fraction of }CO_2\times \text{Total pressure of gas}

\text{Partial pressure of }CO_2=0.75mole\times 300Kpa=225Kpa=225Kpa\times \frac{0.145\text{ psia}}{1Kpa}=32.625\text{ psia}

conversion used : (1 Kpa = 0.145 psia)

Therefore, the partial pressure of the CO_2 in the tank in psia is, 32.6 psia.

3 0
3 years ago
A solution is made by mixing 12.54 grams of NaNO3 with enough water to make 2.5 L of solution. What is the molarity?
Alex

Answer:

is there a table or an equation for that ??

4 0
3 years ago
NEED ANSWER FAST!
lorasvet [3.4K]

Answer:

B

Explanation:

Molarity = 0.010M

Volume = 2.5L

Applying mole-concept,

0.010mole = 1L

X mole = 2.5L

X = (0.010 × 2.5) / 1

X = 0.025moles

0.025moles is present in 2.5L of NaOH solution.

Molar mass of NaOH = (23 + 16 + 1) = 40g/mol

Number of moles = mass / molar mass

Mass = number of moles × molar mass

Mass = 0.025 × 40

Mass = 1g

1g is present in 2.5L of NaOH solution

6 0
3 years ago
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