Many substances have a pH value. Even your blood has a pH value. It's between 7.3 and 7.5. If the pH of your blood falls below 7 or rises above 7.8 you will die. So it can be very important to know pH values. Today we're going to use a humble red cabbage to make a pH indicator.
What you will need:
Half a head of red cabbage
A pot
A large jug or bottle
A sieve or a colander
Several glasses (smaller ones are best)
Colored pencils
Vineger
Water
Bicarbonate of soda
Salt
Various substances for testing (such as lemonade, lemon juice, milk, dish detergent, sports drink, orange juice, washing powder, or fabric softener)
A spoon
A cup of rainwater
+ Ask a grown up to help you chop up half of a red cabbage.
+ Put the cabbage in a cooking pot, cover it with water, bring to a boil and allow the cabbage to boil for about 20 minutes, or until most of the color has steeped out of the cabbage.
+ Leave the mixture to cool to room temperature.
+ Using a sieve or a colander, pour the mixture into a large jug. The cabbage will be caught in the colander (it is perfectly safe to eat). The liquid in the jug is cabbage water indicator. It's color will depend on the water used, but generally it will be a purple color.
+ Set up a row of glasses. This is where you will do your testing. Place about 15 teaspoons of cabbage water indicator into each glass. These are your samples. You should keep one sample as a control so that you can compare your results. When you are testing a solid, add an extra 10 teaspoons of cabbage water to the sample.
+ Add a teaspoon of vinegar to a sample. Stir and wash the spoon. Using your colored pencils, carefully copy the color and label it "vinegar."
1. pH value n. phr.
酸鹼值 (suan1 jian3 zhi2)
2. humble adj.
簡單的 (jian3 dan1 de5)
3. indicator n.
指示劑 (zhi3 shi4 ji4)
4. colander n.
濾器 (lu4 qi4)
5. steep v.t.
浸透 (jin4 tou4)
6. control n.
對照組 (dui4 zhao4 zu3)
7. acid n.
酸性 (suan1 xing4)
8. alkaline n.
鹼性 (jian3 xing4)
9. ion n.
離子 (li2 zi5)
+ The next test is a solid, so first add an extra 10 teaspoons of indicator water. Add a teaspoon of salt to the sample. Stir and wash the spoon. Copy the color and label.
+ Continue to test various household liquids and solids. Always ask permission before handling a substance. NEVER mix household cleaners together.
Remember to be careful when pouring the solutions away, and make sure that you wash the glasses thoroughly after you finish.(catherine Thomas, staff writer)
很多物質都有pH值（即酸鹼值），甚至連血液也有pH值，它介於七點三和七點五之間。如果你血液的pH值小於七或是高於七點八，你就會死亡。因此，知道pH值的大小很重要。今天，我們就要用一般的紫色包心菜來製作pH值指示劑。
所需材料︰
半顆紫色包心菜
一個鍋子
一個大水罐或瓶子
一個篩網或濾器
數個玻璃杯（小玻璃杯最適合）
彩色鉛筆
醋
清水
小蘇打
食用鹽
各式測試物質（如檸檬水、檸檬原汁、牛奶、洗碗精、運動飲料、柳橙原汁、洗衣粉或衣物柔軟精）
一支湯匙
一杯雨水
+ 請大人幫你切下半顆的紫色包心菜。
+ 將切好的包心菜放進鍋子裡，加入水，水面的高度要蓋過包心菜，然後把它煮沸，讓包心菜滾煮約二十分鐘或直到它大部分的顏色都退掉為止。
+ 將鍋中混合物冷卻至常溫。
+ 使用篩網或濾器，將混合物過濾倒至大水罐裡，包心菜會留在濾器上（可安全食用）。水罐裡的液體就是包心菜水指示劑。它的顏色會依據你所使用的水而有所差異，不過通常是呈紫色的。
+ 將玻璃杯排成一排，這將是你進行測試之處。在每個玻璃杯內倒入十五茶匙的包心菜水指示劑，作為你的樣本。其中一個樣本必須當作對照組，這樣你才可以比較實驗的結果。如果你要測試固態物質，請多加十茶匙的包心菜水到樣本中。
+ 加一茶匙的醋到樣本裡，攪拌一下，然後把湯匙洗乾淨。用彩色鉛筆仔細地將顏色記錄下來，然後標示上「醋」。
+ 接下來要測試的是固態物質，所以先多加入十茶匙的指示劑水。加一茶匙的鹽到樣本裡，攪拌一下，然後把湯匙洗乾淨。將顏色記錄下來並標示好。
+ 繼續測試各式家用液體和固態物質。請先獲得大人許可再使用這些東西。千萬不要將家用清潔劑混合在一起。
在倒掉溶液時，記得要小心，使用完畢後，務必將玻璃杯徹底清洗乾淨。（翻譯：楊鴻泰）
What's
the science 科學原理
The pH scale refers to the concentration of hydrogen ions (H). The more hydrogen ions a substance has, the more acidic it is. Acids range from a pH0 (strong) to a pH6 (weakest). Neutral (neither acidic nor alkaline) is pH7. Alkalines or bases have a pH from 8 - 14 (8 is the weakest). The red cabbage contains a natural dye called anthocyanin. When you boil the cabbage, the dye is released into the water. Anthocyanin turns red when it meets acid and green-blue when it meets alkalines.
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