We have an initial amount of H3N2C14 of 72 milligrams, and a half-life of 30 days. Find the decay constant, k, and determine how long it takes for 95% of the material to decay.

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### Problem Statement:

We have an initial amount of \( H_3N_2Cl_4 \) of 72 milligrams, and a half-life of 30 days. Find the decay constant, \(k\), and determine how long it takes for 95% of the material to decay.

### Solution:

#### 1. Finding the Decay Constant, \(k\):

The relationship between the half-life \(T_{1/2}\) and the decay constant \(k\) is given by the formula:

\[
T_{1/2} = \frac{\ln(2)}{k}
\]

Given:
\[
T_{1/2} = 30 \ \text{days}
\]

Rearrange the formula to solve for \(k\):

\[
k = \frac{\ln(2)}{T_{1/2}}
\]

Substitute the given half-life:

\[
k = \frac{\ln(2)}{30} \approx \frac{0.693}{30} \approx 0.0231 \ \text{days}^{-1}
\]

#### 2. Determining the Time for 95% Decay:

We need to find the time \(t\) when 95% of the material has decayed, which means 5% of the original material remains.

The decay formula is:

\[
N(t) = N_0 e^{-kt}
\]

Where:
- \(N(t)\) is the amount of substance remaining at time \(t\),
- \(N_0\) is the initial amount of the substance,
- \(k\) is the decay constant,
- \(t\) is the time.

Since 5% of the original amount remains:

\[
0.05 N_0 = N_0 e^{-kt}
\]

Simplifying the equation by dividing both sides by \(N_0\):

\[
0.05 = e^{-kt}
\]

Take the natural logarithm of both sides:

\[
\ln(0.05) = -kt
\]

Solve for \(t\):

\[
t = \frac{\ln(0.05)}{-k}
\]

Substitute the value of \(k\):

\[
t = \frac{\ln(0.05)}{-0.0231}
\]

Calculate the value of \(\ln(0.05)\):

\[
Transcribed Image Text:### Problem Statement: We have an initial amount of \( H_3N_2Cl_4 \) of 72 milligrams, and a half-life of 30 days. Find the decay constant, \(k\), and determine how long it takes for 95% of the material to decay. ### Solution: #### 1. Finding the Decay Constant, \(k\): The relationship between the half-life \(T_{1/2}\) and the decay constant \(k\) is given by the formula: \[ T_{1/2} = \frac{\ln(2)}{k} \] Given: \[ T_{1/2} = 30 \ \text{days} \] Rearrange the formula to solve for \(k\): \[ k = \frac{\ln(2)}{T_{1/2}} \] Substitute the given half-life: \[ k = \frac{\ln(2)}{30} \approx \frac{0.693}{30} \approx 0.0231 \ \text{days}^{-1} \] #### 2. Determining the Time for 95% Decay: We need to find the time \(t\) when 95% of the material has decayed, which means 5% of the original material remains. The decay formula is: \[ N(t) = N_0 e^{-kt} \] Where: - \(N(t)\) is the amount of substance remaining at time \(t\), - \(N_0\) is the initial amount of the substance, - \(k\) is the decay constant, - \(t\) is the time. Since 5% of the original amount remains: \[ 0.05 N_0 = N_0 e^{-kt} \] Simplifying the equation by dividing both sides by \(N_0\): \[ 0.05 = e^{-kt} \] Take the natural logarithm of both sides: \[ \ln(0.05) = -kt \] Solve for \(t\): \[ t = \frac{\ln(0.05)}{-k} \] Substitute the value of \(k\): \[ t = \frac{\ln(0.05)}{-0.0231} \] Calculate the value of \(\ln(0.05)\): \[
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