A student is given two samples of carbohydrates.
一个学生得到了两个碳水化合物样本。
He tests to see if one is glucose and the other one is starch.
他想要通过测试检验哪一个是葡萄糖，哪一个是淀粉。
Describe the two chemical tests he should use to identify each carbohydrate.
请描述他所做的这两种鉴别碳水化合物的测试分别是什么。
Source:Paper 1 May 2015
试题来源：2015年5月 Paper1
答案
The student can test for glucose using Benedict’s solution. Glucose is added to Benedict’s solution and heated. If glucose is present the solution will turn from blue to yellow (or red or orange).
The student can test for starch using iodine. If starch is present the iodine will turn from yellow to blue/black.
评论
Questions involving tests for glucose and starch are very common, and should be very easy to answer. In my model answer I gave very simple, concise information, which is all that is needed for this ‘describe’ style of question.
I mentioned Benedict’s solution (1 mark) and gave the correct colour change (1 mark). I also mentioned using iodine (1 mark) and gave the correct colour change (1 mark).
在答案中提到Benedict的解决方案（1分），并且指出了颜色变化（1分）。与此同时，还提到了利用碘（1分）的颜色变化（1分）进行区分。
Common pitfalls that my students encounter are:
在教授过得学生中以下是他们常犯的错误：
· Students don’t remember the test
· 学生遗漏测试
· Students don’t remember the correct colour change
· 学生没记住正确的颜色变化
· Students don’t know the meaning of “carbohydrate”
· 学生不知道“carbohydrate”的意思