一些metal reaction問題

Question

1. Predict the observation when excess hydrogen gas is bubbled into AgNO3(aq)

hydrogen 是不是more reactive than Ag? 那是否會有displacement﹖如果有，expected result是不是solution become colourless and some silvery solid is formed?

2. A large amount of NaCl can be obtained from sea water, but Na metal is very expensive, why?

是不是electrolysis是一種很貴的方法﹖如果是，咁點解貴﹖

3. K is more reactive than Na, why?
是不是因為repulsion 大過Na?

4. Na is more reactive than Mg, why?

Answer 1

1.
There is no reaction between hydrogen gas and silver nitrate solution, i.e. no observable change.
Take off hydrogen from displacement reaction of metals. This is because hydrogen is not a metal at all.
Someone puts hydrogen between lead and copper in the reactivity series, in order to help pupils to remember that lead and more reactive metals can react with H+(aq) (dilute acids). However, this may be misleading.

2.
Na is NOT very expensive. At least, Na is much less expensive than gold.
Na is more expensive than NaCl. The price of Na reflects the cost of electrolysis of molten sodium chloride, the cost of storage of Na, the cost of transportation, and also the low demand of Na.

3.
K atom is larger in size than Na, because K has one more electron shell. In K atom, the outermost shell of electron is thus farther apart from the nucleus, and the attraction between the electron in the outermost shell and the nucleus is thus weaker than that in Na. Consequently, the electron in the outermost shell of K atom is lost more readily than Na. In other words, K is more reactive.

4.
Both Na and Mg atoms have 3 electron shells. Na has 11 protons in the nucleus, but Mg has 12. (Besides, the atomic size of Na is greater than that of Mg.) Therefore, the electron in the outermost shell of Na atom is held less tightly and can be lost more readily than Mg.

Answer 2

好清楚~答得幾好