Related questions with answers

Silicon tetrachloride

(\mathrm{SiCl_4})

can be prepared by heating Si in chlorine gas:

\mathrm{Si}(s)+2\mathrm{Cl_2}(g)\rightarrow\mathrm{SiCl_4}(l)

In one reaction, 0.507 mol of

\mathrm{SiCl_4}

is produced. How many moles of molecular chlorine were used in the reaction?

Silicon used in computer chips must have an impurity level below $10^{-9}$ . Silicon is prepared by the reduction of quartz $\left(\mathrm{SiO}_2\right)$ with coke at about $2000^{\circ} \mathrm{C}$ :

\mathrm{SiO}_2+2 \mathrm{C}(s) \longrightarrow \mathrm{Si}(l)+2 \mathrm{CO}(g)

Next, solid silicon is separated from other solid impurities by treatment with hydrogen chloride at $350^{\circ} \mathrm{C}$ to form gaseous trichlorosilane $\left(\mathrm{SiCl}_3 \mathrm{H}\right)$ :

\mathrm{Si}(s)+3 \mathrm{HCl}(g) \longrightarrow \mathrm{SiCl}_3 \mathrm{H}(g)+\mathrm{H}_2(g)

Finally, ultrapure $\mathrm{Si}$ can be obtained by reversing the above reaction at $1000^{\circ} \mathrm{C}$ :

\mathrm{SiCl}_3 \mathrm{H}(g)+\mathrm{H}_2(g) \longrightarrow \mathrm{Si}(s)+3 \mathrm{HCl}(g)

(c) Silicon has a diamond crystal structure. Each cubic unit cell (edge length $a=543 \mathrm{pm}$ ) contains eight $\mathrm{Si}$ atoms. If there are $1.0 \times 10^{13}$ boron atoms per cubic centimeter in a sample of pure silicon, how many $\mathrm{Si}$ atoms are there for every $\mathrm{B}$ atom in the sample? Does this sample satisfy the $10^{-9}$ purity requirement for the electronic grade silicon?

A student is given four solid samples labeled W, X, Y, and Z. All except Z have a metallic luster. She is told that the solids could be gold, lead sulfide, quartz, and iodine. The results of her investigations are as follows: (a) W is a good electrical conductor; X, Y, and Z are poor electrical conductors. (b) When the solids are hit with a hammer, W flattens out, X shatters into many pieces, Y is smashed into a powder, and Z is cracked. (c) When the solids are heated with a Bunsen burner, Y melts with some sublimation, but X, W, and Z do not melt. (d) In treatment with 6 M $\mathrm{HNO}_3$ , X dissolves; there is no effect on W, Y, or Z. On the basis of these test results, identify the solids.

Question

Silicon used in computer chips must have an impurity level below $10^{-9}$ (that is, fewer than one impurity atom for every $10^9 \mathrm{Si}$ atoms). Silicon is prepared by the reduction of quartz $\left(\mathrm{SiO}_2\right)$ with coke (a form of carbon made by the destructive distillation of coal) at about $2000^{\circ} \mathrm{C}$ :
$\mathrm{SiO}_2(s)+2 \mathrm{C}(s) \longrightarrow \mathrm{Si}(l)+2 \mathrm{CO}(g)$
Next, solid silicon is separated from other solid impurities by treatment with hydrogen chloride at $350^{\circ} \mathrm{C}$ to form gaseous trichlorosilane $\left(\mathrm{SiCl}_3 \mathrm{H}\right)$ :
$\mathrm{Si}(s)+3 \mathrm{HCl}(\mathrm{g}) \longrightarrow \mathrm{SiCl}_3 \mathrm{H}(\mathrm{g})+\mathrm{H}_2(\mathrm{~g})$
Finally, ultrapure Si can be obtained by reversing the above reaction at $1000^{\circ} \mathrm{C}$ :
$\mathrm{SiCl}_3 \mathrm{H}(g)+\mathrm{H}_2(g) \longrightarrow \mathrm{Si}(s)+3 \mathrm{HCl}(g)$
Silicon has a diamond crystal structure. Each cubic unit cell (edge length $a=$ $543 \mathrm{pm}$ ) contains eight $\mathrm{Si}$ atoms. If there are $1.0 \times$ $10^{13}$ boron atoms per cubic centimeter in a sample of pure silicon, how many Si atoms are there for every B atom in the sample? Does this sample satisfy the $10^{-9}$ purity requirement for the électronic grade silicon?

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The problem asks to determine the ratio of silicon and boron atoms in a sample of refined silicon given the dimensions of its unit cell and number of boron atoms, as well as if the sample meets the purity requirement of $\mathrm{10^9}$ $\mathrm{Si}$ atoms per $\mathrm{B}$ atom.