回應(會考化學)

回應1

sinying:
真係唔該哂,你個表好有用,我立即抄低了!但係呢,我揾到一條ce mc:
26.On heating, blue copper(II) sulphate crystals gradually change to a white powder. Which of the following statements are correct?
(1)Heat would be liberated if water is added to the white powder.
(2)On further heating, the white powder would turn reddish-brown.
(3)chemical change occurs during the heating of the blue crystals.
A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. (1), (2) and (3)

answer話copper(II) sulphate唔會decomposition,我想問依d compond 係唔係要死記或者好冇方法記架?再一次唔該哂!!

化學友:
sinying，可能化學友上一個嘅回覆唔係太清楚，所以o向e度再講多d丫。

當blue copper(II) sulphate crystal遇熱之後water of crystallization就會放出，剩返white copper(II) sulphate (e.g. CuSO4.5H2O --> CuSO4 + 5H2O)。因為CE只係假設我地知道carbonate, hydrogencarbonate, hydroxide同埋oxide會遇熱分解，所以如果CE問其他ionic compounds會唔會decompose under high temperature，正常o黎講就會當冇decomposition o架啦。所以NaCl, PbCl2, CuSO4或其他ionic compounds都唔會decompose。如果CE條問題要考一隻會decompose嘅ionic compound，佢一定會清楚話比你聽隻compound會decompose。簡單o黎講，當冇特別指示時，我地可以當所有其他ionic compounds遇熱都唔會decompose。所以化學友覺得唔使死記o架。

sinying，唔知答唔答到你嘅問題呢?如果唔得，你再留言丫，化學友再試下再答過啦。

回應2

eddy:
化學友我想問你關於chem個d colour.好似I2咁,係organic solvent係 purple,係佢gas state都係purple.重有無其他係有唔同colour係唔同state加.重有我想問sulphur,bromine,ammonia個d係room temperature係咩colour同邊d係denser than air...唔該哂!!!

化學友:
eddy，o向CE level o黎講剩係得I2會咁樣，其他o野唔會。 至於佢地嘅colour:

sulphur係yellow(好易記o架sulphur係硫磺所以黃色lor。)

bromine係orange

ammonia係colorless

一般o黎講solid同埋liquid嘅density一定高過gas。因為o向室溫sulphur係solid而bromine係liquid，所以sulphur同捚bromine嘅density高過air。

如果兩隻substances都係gas，邊一隻substance嘅relative molecular mass大d，o個一隻substance就有大d嘅density。 NH3嘅relative molecular mass = 14 + 1 x 3 = 17 而air嘅relative molecular mass大約=28x0.8+32x0.2 = 29 (28係N2嘅rleative molecular mass而32係O2嘅relative molecular mass;0.8同埋0.2係佢地o向空氣裡面各自嘅比例。)，所以NH3嘅denisty低過air。明白嗎eddy?