f1 science

1.直接燒(direct heating ),是可以的,我的書中也有例子,但是有風險的,因為有可能會燒裂了watch glass.如果是用water bath,即是燒beaker中的水,再把watch glass 放在上面,蒸汽的熱會轉移到watch glass 中的solution,這樣做的風險是低的,因為我曾heat test tube 的solution,全班的test tube都黑了,有一個還裂了.
2.
(i)水有很大 '比熱容'(specific heat capacity) 是暫時發現最高,是4200,而beaker 是比water小,而愈大的specific heat capacity 表示需要愈多的能量才會溫度上升一度
(ii)熱能的轉移是基於溫度高的向溫度低的,直至兩者溫度相同為止,轉移才會停.
所以在Bunsen burner heat beaker 的一刻,因為beaker 的溫度馬上上升了,變得比water熱,所以熱能從Bunsen burner 到beaker 的一刻,就立即轉移到water.
(iii)熱能的轉移:Bunsen burner －－＞beaker －－＞water,
這個情況不斷出現,直至水boil,變成水蒸氣為止,水蒸汽會帶著熱能離開水,升到 空中,而beaker的溫度,會持在水的boiling point,至大約100度左右.

不知道合5合用呢???

1. watch glass could easily crack if it is heated directly. besides, the heating process is too quick without the beaker, and so the substance is not heated evenly.
2. Water has a high "specific heat capacity". this means that water can absorb heat from the beaker effectively with a relatively small rise in temperature. it is added to prevent the beaker from being overheated and crack.(you can ask your mother what would happen if she heat an empty pot in the stove)

1.點解要擺個watch glass係beaker上面?直接燒watch glass ok?
2.點解要加水係beaker到再燒,唔加有咩影響?
你第１，２條問題其實好相似。
唔直接燒係因為驚影響結果.
因為入面既powder 既沸點我地唔知,　個本生燈d火可以去到3xx度,隨時燒走埋ｄ　powder.

加水落beaker,再用火燒beaker係因為
水既沸點係100度,用水蒸氣再heat 個glass, 咁個glass 就確保大約係100度,只有filtrate入面既水份會蒸發，就唔會怕影既到d powder

我估原因應該係咁