Tin(IV) iodide is prepared by direct combination of the elements. Add 2.00 g of granulated tin to a solution of 6.35 g of iodine. Write an equation for this reaction.


1. Determine the amount of tin using moles = mass/molar mass. This yields a result of 0.017 mol $\ce{Sn}$.

2. Determine the amount of iodine using moles = mass/molar mass. This yields a result of 0.5 mol $\ce{I}$.

3. Determine the ratio of tin to iodine. Using relative amounts, for every 1 mol $\ce{Sn}$ there are 3 mol $\ce{I}$, so the ratio is 1:3. Because iodine is a diatomic molecule, I will adjust accordingly, so the ratio becomes 2 mol $\ce{Sn}$ to 3 mol $\ce{I2}$ or 2:6.

4. Construct the formula:

$$\ce{2Sn + 3I2 -> SnI4}$$

with excess tin and iodine.

Is my procedure correct?

  • $\begingroup$ I think you are overcomplicating it. Your equation doesn't balance so it can't be correct. Surely the correct answer is just $\ce{Sn + 2I2 -> SnI4}$. $\endgroup$ – bon Aug 21 '15 at 13:05

The procedure is correct, be careful with this:

  1. The amount of iodine is 0.050, but the molecular amount () is 0,025.

  2. For the ratio use the amount of point 1 and 2:

$$ \frac{\mathrm{Moles~of~Sn}}{\mathrm{Moles~of~I_2}} = \frac{0.017}{0.025} \approx \frac{2}{3}$$

  1. Don't confuse! This equation is not well balanced. Stoichiometry is inherent of the reaction and is based on Mass Conservation Law; amount of substance tells you which reactive is limiting and which one is in excess.

$$\begin{equation}\ce{Sn + 2I2 \leftrightharpoons SnI4}\tag{The reaction}\end{equation}\\ 0.017 + 0.025 = \,?$$

Now with this you can tell which one is on excess and for how much.

  • 1
    $\begingroup$ Please visit this page, this page and this ‎one on how to make your future posts better.‎ Alternatively, visit this chatroom for further formatting guidance. On chem.SE, we use MathJax for typesetting formulas. $\endgroup$ – M.A.R. Aug 21 '15 at 13:48

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