A student puts some chopped onion in two test tubes.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student puts some chopped onion in two test tubes. She adds dilute hydrochloric acid to one and sodium hydroxide solution to the other. What happens to the smell in each? What kind of indicator is this, and who would find it most useful?
Need a reminder? The key ideaShow
Litmus: an acid turns blue litmus red, a base turns red litmus blue. Phenolphthalein is colourless in acids and pink in bases. Methyl orange is red in acids and yellow in bases. Turmeric is yellow, and turns reddish brown in bases. Onion, vanilla and clove oil lose their smell in a base.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Acid. The smell of onion stays.
Step 2. Base. The smell of onion goes.
Step 3. The kind. An olfactory indicator: it changes its smell, not its colour. It helps a person who cannot see.
Answer: the smell stays in the acid and goes in the base.
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