科學 . 筆記 . Chemistry

~ 07/09/2020 ~

姐姐說上一堂課很無聊，她説題材很好，可是老師教學無趣。姐姐現在很難靜靜坐下來聽課，尤其是她不喜歡的科目，她更是拒絕，還會抗議說：“現在是 Summer，我爲什麽要做這些啊！”😓 自從她有了 iPod Touch，開始玩 roblox, tiktok；還有開始接觸電腦，玩 coding、minecraft 之類的游戲，她變得比較暴躁，整顆心都記挂著這一些，也開始比較不耐煩。在科技迅速發展的時代，要讓小孩只是玩手邊的玩具，畫畫或是動手做之類的，好像變得越來越困難，這些 3C 產品對他們的影響力實在是太大了，不但把他們的靈魂偷走，還偷走了他們的專注力。

可是今天的課題，同樣的題目，同樣的老師，姐弟兩卻非常喜歡。今天是要來破案的。

老師回到學校的科學實驗室，發現地上一片狼藉，爲了要找出蛛絲馬跡，便展開了今天的調查活動（媽媽是太愛做筆記了嗎？他們上課，媽媽在一旁做筆記）


1. 血跡

要查明紙張上的手指印是否沾有血跡

luminol + peroxide --> luminol emits light in the presence of a catalyst (like the iron in blood)

Testing Method:

1. control (e.g. water)
2. bleach
3. blood
4. copper (II) sulfide

2. Testing Fingerprints

• dusting -- use fine brush and fine powder
• Iodine gas -- sticks to fingerprint oils, then becomes solid so that prints can be captured

Through sublimation and deposition, iodine reveals prints for analysis

Dry ice is another material that sublime (turn from solid to gas) in room temperature




3. 測試槍彈殘跡

Testing for Gunshot Residue?

Method 1 : DPA (does it have nitrates and nitrites existed?)

Greiss reagent test for gunpowder.

1. Control - wet brand new swab with water
2. Sample - turns blue color means positive, there is nitrates and nitrites existed

Method 2 : Rhodizonate (does it have heavy metals involved?)

Rhodizonate test turns reddish pink when reacting with lead; orange when reacting with strontium/barium.

1. Control - wet brand new swab with water
2. Sample

4. Fluorescence & UV Light

1. UV light is not visible to the naked eye, but can cause certain chemicals to emit visible light.
2. UV lights can reveal substances at crime scenes that would not otherwise be visible.
3. UV light can make chromatograms of chemical panels visible.

Fluorescence helps us see evidence that our eyes normally cannot