Question 1

Which functional group is present in multiple copies in both glucose and fructose, allowing them to react with copper(II) hydroxide in alkaline solution?

Accepted Answer

Hydroxyl group

Question 2

During the experiment, why is it important to prepare the copper(II) hydroxide precipitate freshly in the test tube rather than using a precipitate prepared earlier?

Accepted Answer

Freshly prepared Cu(OH)$$_2 is $$more reactive and sensitive for detecting organic compounds with multiple hydroxyl groups.

Question 3

What is the observable color change when glucose or fructose is added to the mixture of NaOH and CuSO$$_4 in $$the test tube?

Accepted Answer

The solution turns blue due to the formation of a copper(II) complex.

Question 4

Which step in the experiment is used to identify organic compounds with multiple hydroxyl groups?

Accepted Answer

Step 4: Adding glucose or fructose and observing the dissolution of the precipitate and color change.

Question 5

Why should the test tube NOT be heated during this experiment?

Accepted Answer

Heating may cause decomposition of the copper(II) complex, leading to inaccurate results.

Question 6

If you accidentally spill NaOH solution on your skin during the experiment, what is the best immediate action?

Accepted Answer

Rinse the affected area with plenty of water immediately.

Question 7

Which of the following best explains why glucose and fructose can dissolve the Cu(OH)$$_2$$ precipitate in alkaline solution?

Accepted Answer

They form a stable blue complex with copper(II) ions due to their multiple hydroxyl groups.

Question 8

In the preparation of Cu(OH)$$_2 in $$the test tube, how should the volumes of NaOH and CuSO$$_4$$ solutions be related?

Accepted Answer

The volume of NaOH should be greater than that of CuSO$$_4.$$

Question 9

Which laboratory skill is essential for ensuring complete reaction and accurate observation in this experiment?

Accepted Answer

Gently shaking the test tube using the wrist to mix the chemicals.

Question 10

What is the main practical application of the reaction between glucose (or fructose) and freshly prepared Cu(OH)$$_2 in $$alkaline solution?

Accepted Answer

It is used to detect the presence of reducing sugars in food and biological samples.

Question 11

A student observes that after adding glucose to the blue Cu(OH)$$_2$$ precipitate in NaOH, the solution turns clear blue. What does this indicate?

Accepted Answer

Glucose has formed a soluble complex with copper(II) ions.

Question 12

Which of the following is a safety precaution that must be followed when handling NaOH solution in this experiment?

Accepted Answer

Wear gloves and goggles to protect skin and eyes from chemical burns.

Question 13

Which of the following best describes the chemical property of glucose and fructose that is tested in this experiment?

Accepted Answer

Their ability to act as reducing sugars due to multiple hydroxyl groups.

Question 14

If a student uses twice as much CuSO$$_4 as $$NaOH in the preparation of Cu(OH)$$_2$$, what is the most likely outcome?

Accepted Answer

Not all Cu$$^{2+}$$ ions will precipitate as Cu(OH)$$_2$$, resulting in incomplete reaction.

Question 15

Which of the following equations best represents the formation of copper(II) hydroxide from copper(II) sulfate and sodium hydroxide?

Accepted Answer

$$\mathrm{CuSO_4 + 2NaOH \rightarrow Cu(OH)_2 \downarrow + Na_2SO_4}$$

Question 16

Which of the following best explains why the experiment should be performed at room temperature?

Accepted Answer

Higher temperatures may cause decomposition of the copper(II) complex, affecting the sensitivity of the test.

Question 17

Which of the following is NOT a correct laboratory technique for this experiment?

Accepted Answer

Heating the test tube to speed up the reaction.

Question 18

A solution turns blue after adding glucose to a freshly prepared Cu(OH)$$_2$$ precipitate in NaOH. What does this color indicate about the chemical species present?

Accepted Answer

A soluble copper(II)-glucose complex has formed.

Question 19

Which of the following best describes the role of NaOH in the experiment?

Accepted Answer

It provides an alkaline environment necessary for the formation of Cu(OH)$$_2$$ and the subsequent complexation with glucose or fructose.

Glucose and Fructose: Chemical Properties and Laboratory Identification (GOB Chemistry Lab Study Notes)

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