Chemistry Questions and Answers

Answer: A

The electron makes 4 waves.

A magnetic quantum number of \(m_l=+3\) requires \(l\ge 3\), and since \(l\) can be at most \(n-1\), the smallest possible principal quantum number is \(n=4\).

De Broglie's condition for a stable orbit is \[2\pi r = n\lambda\] so the number of complete waves in the orbit equals \(n\), giving 4.

Answer: C

Shaving creams use soft soaps.

Soft soaps are the potassium salts of fatty acids, made with potassium hydroxide instead of sodium. They are more soluble than the sodium (hard) soaps, lather freely and are gentler on skin. Calcium and lead soaps are insoluble and are used as greases and driers.

Answer: A

Ozone is concentrated in the stratosphere.

The ozone layer lies between about 15 and 35 km, where ultraviolet light splits \(\mathrm{O_2}\) and the free atoms combine with more \(\mathrm{O_2}\). The heat released is why the stratosphere, uniquely, grows warmer with height.

Answer: C

The ozone layer is depleted by man-made compounds containing both fluorine and chlorine.

Chlorofluorocarbons drift up to the stratosphere, where ultraviolet light frees a chlorine atom that then destroys ozone catalytically: \[\mathrm{Cl + O_3 \rightarrow ClO + O_2},\qquad \mathrm{ClO + O \rightarrow Cl + O_2}\] One chlorine atom can destroy tens of thousands of ozone molecules before it is removed.

Answer: D

Natural rubber is a polymer of isoprene.

It is cis-1,4-polyisoprene, and the all-cis geometry is what gives it elasticity, since the chains cannot pack neatly. Gutta-percha is the trans isomer of the same polymer and is hard and inelastic.