Statements about heavy water are given below.
A. Heavy water is used in exchange reactions for the s

Q: Why is $D_2O$ used in exchange reactions?

Because deuterium is chemically identical to hydrogen but has a different mass, it can be used as a 'tracer'. By replacing hydrogen with deuterium, chemists can track the movement of atoms during a reaction using techniques like NMR or mass spectrometry.

Q: What exactly is 'exhaustive electrolysis'?

It means continuously electrolyzing a huge amount of water for a very long time. Since $H_2O$ electrolyzes faster than $D_2O$, the remaining liquid becomes progressively richer in $D_2O$ until it is almost pure heavy water.

Q: Why does $D_2O$ have a higher boiling point?

The heavier mass of the deuterium atom lowers the zero-point energy of the molecule, which effectively makes the hydrogen bonds in $D_2O$ slightly stronger than those in $H_2O$. Stronger bonds require more heat to break, hence a higher boiling point.

Q: What is viscosity and why is $D_2O$ more viscous?

Viscosity is a liquid's resistance to flow. Because the intermolecular hydrogen bonds in $D_2O$ are stronger, the molecules 'stick' together more tightly, making it harder for them to flow past each other compared to $H_2O$.

Q: Is heavy water safe to drink?

In very small amounts, yes. However, because the $O-D$ bond is stronger than the $O-H$ bond, drinking large amounts of heavy water slows down critical biochemical reactions in your body, which can be toxic and eventually fatal.

Question

Statements about heavy water are given below.
A. Heavy water is used in exchange reactions for the study of reaction mechanisms.
B. Heavy water is prepared by exhaustive electrolysis of water.
C. Heavy water has higher boiling point than ordinary water.
D. Viscosity of $H_2O$ is greater than $D_2O$.
Which of the given statements are correct?

Options:

(A) A, B and C

(B) Only A and B

(C) Only A and D

(D) Only A and C

Sigma Percentile · Accepted Answer

Let's dive into the fascinating world of heavy water, chemically known as $D_2O$. It looks and feels just like ordinary water, but the subtle substitution of hydrogen with its heavier isotope, deuterium, brings about some remarkable changes in its physical and chemical properties. We will analyze each statement given in the question to uncover the truth about heavy water.

### Analyzing Statement A: Exchange Reactions

Statement A claims that heavy water is used in exchange reactions for the study of reaction mechanisms. This is absolutely true! Because deuterium is chemically similar to hydrogen but has twice the mass, it acts as an excellent 'tracer'.

When a compound containing hydrogen is placed in heavy water, the hydrogen atoms can swap places with the deuterium atoms. For example, if we dissolve sodium hydroxide in heavy water, an equilibrium is established:

$$NaOH + D_2O ightleftharpoons NaOD + HDO$$

By tracking where the deuterium ends up, chemists can deduce the step-by-step mechanism of complex chemical reactions. So, Statement A is correct.

### Analyzing Statement B: Preparation by Electrolysis

How do we even get heavy water? Statement B says it is prepared by the exhaustive electrolysis of water. This is also true, and the reason behind it is a beautiful concept called the **Kinetic Isotope Effect**.

The $O-H$ bond in ordinary water is slightly weaker and easier to break than the $O-D$ bond in heavy water. When we pass an electric current through a large volume of ordinary water (which naturally contains a tiny fraction of $D_2O$), the $H_2O$ molecules are electrolyzed into hydrogen and oxygen gases much faster than the $D_2O$ molecules.

If we continue this process exhaustively, the ordinary water is essentially 'boiled off' electrically, leaving behind a highly concentrated solution of heavy water. Thus, Statement B is correct.

### Analyzing Statement C: Boiling Point

Statement C states that heavy water has a higher boiling point than ordinary water. Let's think about the physics here. Deuterium is heavier than protium (normal hydrogen). This increased mass leads to slightly stronger intermolecular forces, specifically stronger hydrogen bonding, in $D_2O$ compared to $H_2O$.

Because the molecules are held together more tightly, it takes more thermal energy to break them apart and turn the liquid into a gas. The boiling point of ordinary water is $373\,	ext{K}$, while the boiling point of heavy water is $374.4\,	ext{K}$. Therefore, Statement C is correct.

### Analyzing Statement D: Viscosity

Finally, let's look at Statement D, which claims that the viscosity of $H_2O$ is greater than that of $D_2O$. Viscosity is essentially a fluid's resistance to flow—think of it as the 'thickness' of the liquid.

As we established earlier, the intermolecular forces in heavy water are stronger due to the heavier deuterium atoms. Stronger forces mean the molecules have a harder time sliding past one another. Consequently, heavy water is more viscous than ordinary water.

The actual values are $0.8903\,	ext{cP}$ for $H_2O$ and $1.107\,	ext{cP}$ for $D_2O$. Since $D_2O$ is more viscous, Statement D is **incorrect**.

### Final Conclusion

Summarizing our analysis, Statements A, B, and C are factually correct, while Statement D is false. Therefore, the correct combination of true statements is A, B, and C, making option (a) the right answer.

Select Answer:

Visualized Solution

$D_{2} O vs H_{2} O$

\text{Statement A: Exchange Reactions}

\text{Statement B: Preparation}

\text{Statement C: Boiling Point}

\text{Statement D: Viscosity}

\text{Conclusion}

The Sigma Insight: Hydrogen, Hydrides and Water

Analyzing Statement A

Analyzing Statement B

Analyzing Statement C

Analyzing Statement D

Final Conclusion

Similar Questions

Which one of the following statements about water is false?

The correct statements about $H_{2} O_{2}$ are (A) used in the treatment of effluents. (B) used as both oxidising and reducing agents. (C) the two hydroxyl groups lie in the same plane. (D) miscible with water. Choose the correct answer from the options given below.

In context with the industrial preparation of hydrogen from water gas ( $CO + H_{2}$ ), which of the following is the correct statement ?

Dihydrogen of high purity ( $> 99.95%$ ) is obtained through

From the following statements regarding $H_{2} O_{2}$ , choose the incorrect statement.