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Question Video: Explaining Why Water Baths Should Be Used Rather than Bunsen Burners Biology

When carrying out the test for reducing sugars using Benedict’s reagent, the mixture should be heated in a water bath. Why should a water bath be used rather than a Bunsen burner?

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Video Transcript

When carrying out the test for reducing sugars using Benedict’s reagent, the mixture should be heated in a water bath. Why should a water bath be used rather than a Bunsen burner? (A) It is too dangerous to use a Bunsen burner near Benedict’s reagent. (B) A Bunsen burner should only be used to heat up water, not other mixtures. (C) It is easier to maintain a constant temperature when using a water bath. (D) A Bunsen burner will not reach the required 75 degrees Celsius to heat the mixture. Or (E) this is incorrect; a Bunsen burner should be used.

Let’s think about the two heating options presented in this question. What’s the difference in heating a mixture with a water bath versus a Bunsen burner?

Bunsen burners provide more direct heating and raise the heat quickly to high temperatures, which is why they are used for sterilization and combustion. This quick increase in temperature can be a problem as it is not easily controlled. Bunsen burners can also cause pockets of very hot solution and areas where the solution is at a lower temperature. So the temperature of the solution being heated is not equally distributed.

When a test tube is placed in a hot water bath, its contents are completely immersed in the hot liquid, causing uniform heating. It is also very easy to create a constant temperature when using a water bath as opposed to other heating methods. Water baths can be used to heat solutions up to 100 degrees Celsius, but no higher, seeing as this is the boiling point of water. The temperature usually used to drive the reducing reaction in a Benedict’s test is 90 degrees Celsius, so the water bath can do this. And it would allow the experimenter to monitor the temperature easily.

Therefore, the correct answer to this question is (C). A water bath should be used, rather than a Bunsen burner, to heat the mixture in a Benedict’s test, because it is easier to maintain a constant temperature when using a water bath.

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