Chapter 6: Problem 6
What metal is generally added to steel to make it corrosion resistant?
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Light-emitting diodes (LEDs) contain \(\mathrm{P}-\mathrm{n}\) junctions. The circuit in an LED is arranged so that electrons from the power source flow into the conduction band of the n-type side. As electrons continue to flow, they are pushed to the conduction band of the p-type side, which can hold more electrons. These electrons enter the conduction band of the p-type side, because they already occupy the higher-energy band in the n-type side. However, once the electrons are in the higher-energy band of the p-type side, they fall into the lower-energy band unless it is full. As these electrons make transitions to the lower-energy band, energy is released in the form of light. (a) Explain, in terms of the movement of electrons, why an LED cannot be made from the junction of pure silicon and silicon doped with phosphorus. (b) If the direction of the circuit in the LED is reversed, so that the electrons flow from the power source into the \(\mathrm{p}\)-type side of the \(\mathrm{p}-\mathrm{n}\) junction directly, where would the electrons go once they enter the \(\mathrm{p}-\mathrm{n}\) junction? (That is, indicate which bands would receive the electrons and whether the electrons would then migrate to other bands.) (c) Would you expect the LED to emit light when it is placed in the reverse circuit described in part (b)? Explain your answer.
Iron pyrite \(\left(\mathrm{FeS}_{2}\right)\) is known as Fool's Gold because of its resemblance to gold metal. However, it can easily be distinguished from gold by the difference in their densities. The density of gold is \(19.28 \mathrm{~g}^{\mathrm{cm}} \mathrm{cm}^{3}\) and that of Fool's Gold is \(5.01 \mathrm{~g}^{\prime} \mathrm{cm}^{3}\). What volume of Fool's Gold would have the same mass as a \(4.0 \mathrm{~cm}^{3}\) piece of gold?
Solid silicon carbide reacts with molten sodium hydroxide and oxygen gas at high temperatures to form solid \(\mathrm{Na}_{2} \mathrm{SiO}_{3}\), gaseous water, and carbon dioxide. Write a balanced equation for the reaction.
What is the oxidation number of (a) phosphorus in \(\mathrm{Li}_{7} \mathrm{P}_{3} \mathrm{~S}_{11}\), which forms in some ceramic electrolytes; (b) titanium in \(\mathrm{BaTiO}_{3}\) ?
Use the VSEPR model to estimate the \(\mathrm{Si}-\mathrm{O}-\mathrm{Si}\) bond angle in silica.
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