(1) Calculate rate (k) at first order

$\overline{){\mathbf{k}}{\mathbf{}}{\mathbf{=}}{\mathbf{}}\frac{\mathbf{ln}\mathbf{\left(}\mathbf{2}\mathbf{\right)}}{{\mathbf{t}}_{\mathbf{1}\mathbf{/}\mathbf{2}}}}\phantom{\rule{0ex}{0ex}}\mathbf{k}\mathbf{}\mathbf{=}\mathbf{}\frac{\mathbf{ln}\mathbf{\left(}\mathbf{2}\mathbf{\right)}}{\mathbf{4}\mathbf{.}\mathbf{5}\mathbf{}\overline{)\mathbf{days}}\mathbf{}\mathbf{\left(}{\displaystyle \frac{24\mathrm{hrs}}{1\overline{)\mathrm{day}}}}\mathbf{\right)}}$

k = 6.42x10^{-3} hrs^{-1}

(2) **t = 48 hours**

**Initial mass = ??**

Mass remaining = 5.0 g

A chemist wishing to do an experiment requiring ^{47}Ca^{2+} (half-life = 4.5 days) needs 5.0 ug of the nuclide. What mass of ^{47}CaCO_{3} must be ordered if it takes 48 h for delivery from the supplier? Assume that the atomic mass of ^{47}Ca is 47.0 u.

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