Video Transcript
Benedict’s solution is used to test
samples for the presence of sugars. The results from multiple tests are
shown in the diagram. Which of the following options
correctly describes the proportions of reducing sugars in the samples shown in the
diagram? (A) X has moderate amounts of
reducing sugars, Y has a high proportion of reducing sugars, and Z has small traces
of reducing sugars. (B) X has a high proportion of
reducing sugars, Y has moderate amounts of reducing sugars, and Z has small traces
of reducing sugars. (C) X has small traces of reducing
sugars, Y has a high proportion of reducing sugars, and Z has moderate amounts of
reducing sugars. (D) X has small traces of reducing
sugars, Y has moderate amounts of reducing sugars, and Z has a high proportion of
reducing sugars.
Sugars, or carbohydrates, are a
large part of our diets and are essential reactants in cellular respiration. An example of a sugar you will
commonly consume is glucose, which is a simple sugar also known as a
monosaccharide. Monosaccharides are reducing sugars
and can be tested for using Benedict’s reagent. Let’s take a look at how Benedict’s
reagent is a blue solution that contains a mixture of chemicals, including copper
oxide. When Cu2+ ions in this copper oxide
are exposed to reducing sugars, they gain an electron to become Cu+ ions. This reaction forms a red
precipitate.
The more reducing sugars present,
the more red precipitate is formed. So, sample Z must have a lot of
reducing sugars present, because the solution has turned a brick-red color. Moderate amounts of sugar will
produce a yellow colored solution. And small amounts of reducing
sugars will only slightly change the color of the Benedict’s reagent from blue to
green. So, from sample X to sample Z, we
can see the amount of reducing sugars present is increasing.
Using this knowledge, let’s look
back at our answer choices. The option that correctly describes
the proportions of reducing sugars in the samples is (D). X has small traces of reducing
sugars, Y has moderate amounts of reducing sugars, and Z has a high proportion of
reducing sugars.
