chemistry questions!!

2009-05-20 3:53 am

In a serues of laboratory experiments, the oxides of Mg, Ca, Sr and Ba were shaken in a test tube with deionised wawter. Afterwards, the contents of each test tube were tested with a pH meter and it was found that, on progressing from magnesium oxide to barium oxide, the pH increased from ~7 to ~14.

(i) why should the pH, in any of these experiments, be greater than 7?

(ii)Write an ionic equation for any reaction that occurs.

(iii)Explain the increase in pH on progressing from magnesium oxide to barium oxide.

(iv) State, with your reason, what type of chemical reaction occurs in these experiments.

Type of reaction:

Reason:

回答 (1)

冷眼旁觀

2009-05-20 9:17 pm

✔ 最佳答案

(i)
MgO does not react with water. Therefore, it does not change the pH of water, and the final pH is about 7.

CaO, SrO, and BaO can react with water to give Ca(OH)2, Sr(OH)2 and Ba(OH)2 respectively. All of these hydroxides can dissolve in water with low solubilities to give the corresponding metal ions and hydroxide ions. The presence of aqueous hydroxide ions makes the pH greater than 7.

(ii)
CaO(s) + H2O(l) → Ca2+(aq) + 2OH-(aq)
SrO(s) + H2O(l) → Sr2+(aq) + 2OH-(aq)
BaO(s) + H2O(l) → Ba2+(aq) + 2OH-(aq)

(iii)
This is due to the fact the MgO does not react with water and the increase in solubility on progressing from calcium hydroxide to barium hydroxide.

(iv)
Answer 1:
Type of reaction: hydrolysis
Reason: reaction with water

Answer 2:
Type of reaction: neutralization (Bronsted-Lowry)
Water is proton donor, and the oxide ion is a proton acceptor.

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