Radioactive decay => C = Co { e ^ (- kt) |
Data:
Co = 2.00 mg
C = 0.25 mg
t = 4 hr 39 min
Time conversion: 4 hr 39 min = 4.65 hr
1) Replace the data in the equation to find k
C = Co { e ^ (-kt) } => C / Co = e ^ (-kt) => -kt = ln { C / Co} => kt = ln {Co / C}
=> k = ln {Co / C} / t = ln {2.00mg / 0.25mg} / 4.65 hr = 0.44719
2) Use C / Co = 1/2 to find the hallf-life
C / Co = e ^ (-kt) => -kt = ln (C / Co)
=> -kt = ln (1/2) => kt = ln(2) => t = ln (2) / k
t = ln(2) / 0.44719 = 1.55 hr.
Answer: 1.55 hr
The mass percentage of Na in NaCl is 39.0%
This means that if there's 100 mg of NaCl , 39 mg of the compound is Na.
For compound to contain 39 mg Na - 100 mg of NaCl should be present.
Therefore for the compound to contain 400 mg - 100/39 x 400 - 1025.6 mg
The mass of NaCl present should be 1.026 g
Answer:
The 2 zeros after the decimal point
