Question

إضافة حمض الهيدروكلوريك المخفف إلى ثلاثة أملاح صلبة (C ، B ، A) كل على حدة:

• في حالة (A) تصاعد غاز عديم اللون.
• في حالة (B) تصاعد غاز يتأكسد في الهواء.
• في حالة (C) لم يحدث تفاعل.

أي مما يلي يعبر عن أنيونات هذه الأملاح؟

• A. $SO_3^{2-}$ : (C), $S_2O_3^{2-}$ : (B), $NO_2^-$ : (A)
• B. $PO_4^{3-}$ : (C), $NO_2^-$ : (B), $CO_3^{2-}$ : (A)
• C. $CO_3^{2-}$ : (C), $NO_2^-$ : (B), $SO_4^{2-}$ : (A)
• D. $PO_4^{3-}$ : (C), $SO_3^{2-}$ : (B), $CO_3^{2-}$ : (A)

Answer 1

Answer: (B)

Option ②: $PO_4^{3-}$ : (C), $NO_2^-$ : (B), $CO_3^{2-}$ : (A)

Answer 2

The problem describes the reactions of three solid salts (A, B, C) with dilute hydrochloric acid (HCl). Let's analyze each case to identify the anions:

• Salt A (Colorless gas evolved): This indicates the presence of an anion that reacts with dilute HCl to produce a colorless gas, such as carbonate ($CO_3^{2-}$). The reaction is: $CO_3^{2-} (aq) + 2HCl (aq) \rightarrow 2Cl^- (aq) + H_2O (l) + CO_2 (g)$.

• Salt B (Gas oxidizes in air): This is characteristic of the nitrite ion ($NO_2^-$). Nitrite reacts with dilute acids to produce nitric oxide ($NO$), a colorless gas that readily oxidizes in air to form reddish-brown nitrogen dioxide ($NO_2$). The reactions are: $3NO_2^- (aq) + 2H^+ (aq) \rightarrow NO_3^- (aq) + 2NO (g) + H_2O (l)$ and $2NO (g) + O_2 (g) \rightarrow 2NO_2 (g)$.

• Salt C (No reaction): This indicates the presence of an anion that does not react with dilute HCl, such as phosphate ($PO_4^{3-}$).

Therefore, the correct option is ②: $PO_4^{3-}$ : (C), $NO_2^-$ : (B), $CO_3^{2-}$ : (A).