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CHEM 2000 MC Q.18 AND Q22
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CHEM 2000 MC Q.4 AND Q.11 可唔可以解釋下個答案問黎? 更新: CHEM 2000 MC Q.18 AND Q22先係 唔係CHEM 2000 MC Q.4 AND Q.11
最佳解答:
18. when potassium carbonate is added to a sample of tap water, some cloudy precipitate is formed. This is because of precipitation between metals and the carbonate ion. (Because group I metal ions will never precipitate with any anions. So it has nothing to deal with the anions. So, C and D are the the required ans.) For A, ammonium compounds always dissolves in water and no precipitate is formed. So, B is the answer. Mg2+(aq) + CO3 2-(aq) → MgCO3 (s) 22. The answer is D. For A, when calcium oxide dissolves in water, it is calcium hydroxide solution. CaO (s) + H2O (l) → Ca(OH)2 (aq) And calcium hydroxide reacts with an acid to give salt and water ONLY (neutralization.) Ca(OH)2 (aq) + 2HCl (aq) → CaCl2 (aq) + 2H2O (l) For B, calcium carbonate is INSOLUBLE in water. So it is wrong. For C, similarly, it reacts with HCl to give salt and water only. So, D is the ans. For D, K2CO3 (aq) + 2HCl (aq) → 2KCl (aq) + CO2 (g) + H2O (l) carbon dioxide is formed.
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