|
TOEFL Directory > TOEFL writing > Listening Unit one passage 20
Listening Unit one passage 20
Listen to the passage again and check out the script.
★Listen to part of a talk in a Chemistry class
Today I'd like to provide some examples of how to work of chemists plays a role in our everyday lives. So for starters, I brought two bottles of vanilla flavoring with me. At time that like be found in your kitchens, one is labeled "the vanilla extract?and the other is labeled "imitation the vanilla extract.? Now both the substances taste the same, because they contain the vanillin accuse, and tastes were related to the regular structure, so what' the difference then between the two? Well, realism the extract at alcohol and water solution of materials that have been abstracted from the vanilla beans, imitation the minor abstract on the other hand is made from a constituent of wood called lignin, this lignin is converted to vanillin, the same molecule found in natural vanilla extracts, now why would chemists go through this process? Now it cost about half as much to produce a gallon the fake vanilla as cost to produce a gallon the real stuff, which is real advantage for the consumer. So how do we know that product test being flossing labels and would buy the real thing? We will be full these products with labels. Chemists has determined the sources of the vanillin molecules by determining the ratio of the C12 to C13 atoms in the vanillin, the ratio of these atoms is slightly different from natural and imitation vanillin, and from this slight differences that chemists can tell if the vanillin is real or imitation. Ok, before we go on, why don't you come up to see if you can smell the difference between these two products?
Correct answers :CBBAD
|
