chem Q about alkalis

☆ 天與空 ★ ◤

2007-04-06 7:22 pm

1). A sodium hydroxide solution has been exposed to air for a long time. When dilute hydrochloric acid is added to it, colorless gas bubbles are given out. Explain the observation with the help of equations.

2). A solution of ammonia has a strong smell of ammonia gas. What does this tell you about the particles present in the solution?

please solve them....thanks a lot

回答 (1)

Uncle Michael

2007-04-06 11:17 pm

✔ 最佳答案

(1)
Sodium hydroxide reacts with carbon dioxide gas to give a solution of sodium carbonate. If sodium hydroxide solution is exposed in air for a long time, the reaction will go complete.
2NaOH(aq) + CO2(g) → Na2CO3(aq) + H2O(l)
or 2OH-(aq) + CO2(g) → CO32-(aq) + H2O(l)

When dilute hydrochloric acid is added to the solution, sodium carbonate in the solution would react with the hydrochloric acid to give colourless bubbles of carbon dioxide gas.
Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)
or : CO32-(aq) + 2H+(aq) → H2O(l) + CO2(g)

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(2)
Ammonia molecules are present in the ammonia solution. Some ammonia molecules would escape from the solution to become ammonia solution, which has a characteristic smell.

2007-04-06 15:18:58 補充：
(2)........................ the solution to become ammonia gas (not solution), which ......

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