Q.
Show with diagrams why hydrochloric acid is used in the test for non-reducing sugars (e.g. sucrose)

A.
Sucrose is a combination of two simple sugars, fructose and glucose. The two simple sugars are combined in a way that gives a negative test for glucose or other reducing sugars. Hydrochloric acid will cause sucrose to break down into the two simple sugars from which it is composed. Study the diagrams below:

Glucose (or other reducing sugar) -----> Positive Benedict test

Sucrose (or other non-reducing sugar) ----> Negative Benedict test

Sucrose + HCl -------> glucose + fructose ----> Positive Benedict test

You can improve on the above diagrams if you spend enough time to understand them.

Related Reaction Rates

Q.
The average rate of disappearence of ozone in the reaction 2O3(g) --> 3O2(g) is found to be 3.0 x 10^-3 atm/sec over a certain interval of time. What is the rate of appearance of O2 during this interval?

A.
The mole ratio of O2(oxygen) to O3(ozone) is 3/2, the ratio of the two coefficients in the balanced chemical equation. Here, the partial pressure ratio, P(O2)/P(O3), of the two gases is also 3/2. The Ideal Gas Law written in subscript form is:
P1V1/P2V2 = n1T1/n2T2
If the temperatures and volumes are the same, this simplifies to:
P1/P2 = n1/n2 (pressure ratio = mole ratio)
or
P(O2)/P(O3) = n(O2)/n(O3) = 3/2
or
P(O2) = P(O3)*[ n(O2)/n(O3)]
or
P(O2) = P(O3)*[3/2]
(3.0 x 10^-3 atm.O3/sec)[(3 atm.O2/s)/(2 atm.O3/s)]=4.5x10^-3 atm.O2/s
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