Question

Попытайтесь объяснить, почему для получения газообразного HCl,берут твердый NaCl и концентрированную серную кислоту. Что произойдет, если реакцию проводить в разбавленном растворе. Почему для получения H2S по аналогичному способу можно использовать разбавленные растворы Na2S и H3PO4.

Answer 1

Потому что только концентрированная серная кислота может вытеснить соляную из соли, иначе в растворах будут находиться ионы натрия, хлорид-ионы и сульфат-ионы. Хлороводород - сильная кислота, поэтому в растоворе диссоциирует полностью, т.е. обладает огромной растворимостью.  

Answer 2

Formation of HCl Gas from Solid NaCl and Concentrated Sulfuric Acid

When solid sodium chloride (NaCl) reacts with concentrated sulfuric acid (H2SO4), it produces hydrogen chloride (HCl) gas. The reaction can be represented as follows:

NaCl(s) + H2SO4(l) → NaHSO4(s) + HCl(g)

The reason for using concentrated sulfuric acid is that it is a strong dehydrating agent. It reacts with sodium chloride to form sodium bisulfate and hydrochloric acid gas. The reaction is driven by the strong affinity of sulfuric acid for water, which allows it to remove water from the sodium chloride, leading to the formation of hydrochloric acid gas.

Effect of Conducting the Reaction in Dilute Solution

If the reaction is conducted in a dilute solution instead of using concentrated sulfuric acid, the reaction will not proceed as expected. Dilute sulfuric acid does not have the same dehydrating properties as concentrated sulfuric acid. Therefore, it will not effectively remove water from the sodium chloride to produce hydrochloric acid gas. Instead, the reaction may result in the formation of a dilute solution of hydrochloric acid, but the production of HCl gas will be significantly reduced or may not occur at all.

Formation of H2S from Na2S and H3PO4

Similarly, hydrogen sulfide (H2S) gas can be produced by reacting a dilute solution of sodium sulfide (Na2S) with dilute phosphoric acid (H3PO4). The reaction can be represented as follows:

Na2S(aq) + 2H3PO4(aq) → 2NaH2PO4(aq) + H2S(g)

In this reaction, the dilute phosphoric acid reacts with the sodium sulfide to produce sodium dihydrogen phosphate and hydrogen sulfide gas. The use of dilute solutions in this case is effective because the reaction does not require the strong dehydrating properties of concentrated sulfuric acid. Instead, the reaction proceeds due to the specific chemical properties of the substances involved.

In summary, the choice of concentrated or dilute solutions in these reactions is based on the specific chemical properties and reactivity of the substances involved, as well as the desired products of the reactions.