Tag: chemistry

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Multiple choice chemistry hard water and soft water heavy water study of heavy water hydrogen and its compounds

Which of the following is not true?

  1. Hardness of water depends on its behaviour towards soap

  2. The temporary hardness is due to the presence of Ca and Mg bicarbonates

  3. Permanent hardness is due to the presence of soluble Ca and Mg sulphates

  4. Permanent hardness can be removed by boiling the water
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Permanent hardness is the hardness that cannot be removed by boiling. It is usually caused by the presence of calcium sulphate or magnesium sulphates or chlorides, nitrates of Ca, Mg in the water which does not precipitate out as the temperature increases.


Hence, option D is correct.

Multiple choice chemistry hard water and soft water heavy water study of heavy water hydrogen and its compounds

The boiling point of $D _{2}O$ is greater than $H _{2}O$. It is because:

  1. $D _{2}O$ has lower $K _w $ value
  2. $D _{2}O$ has a lower dielectric constant
  3. $D _{2}O$ is a associated liquid
  4. the molecular weight of $D _{2}O$ is greater than $H _{2}O$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$D _2O$ has a somewhat higher boiling point because its molecular weight is about $(16+2+2=20)$ and $H _2O$ is about $(16+1+1=18)$.

Multiple choice chemistry hard water and soft water heavy water study of heavy water hydrogen and its compounds

Compare the bond energy (B.E) of $O-H$ in water and $O-D$ in heavy water:

  1. B.E of $O-H >$ B.E of $O-D$
  2. B.E of $O-H <$ B.E of $O-D$
  3. B.E of $O-H =$ B.E of $O-D$
  4. B.E of $O-H =$ 2 times B.E of $O-D$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Boiling point of heavy water is more than normal water and therefore, bond energy of $O-H$ bond in water is lesser than bond energy of $O-D$ bond in heavy water. 


Also, bond length of $O-H$ is greater than $O-D$ and bond energy is inversely proportional to bond energy.

Multiple choice chemistry hard water and soft water heavy water study of heavy water hydrogen and its compounds

Heavy water is obtained by ?

  1. boiling water
  2. heatiing $H _{2}O _{2}$
  3. Prolonged electrolysis of $H _{2}O$

  4. All of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$D _{2}O$ is prepared by repeated electrolysis of ordinary water which contains a small amount of alkali. Ordinary water contains a very very small fraction (about 1 part in 6000 parts) of heavy water.

Multiple choice chemistry hard water and soft water heavy water study of heavy water hydrogen and its compounds

Atomic nuclear reactors use heavy water. This is different from ordinary water only to the extent that in place of hydrogen it contains:

  1. deuterium, a heavier isotope of hydrogen

  2. nitrogen, which is also a light element

  3. tritium, an heavier isotope of hydrogen

  4. a radioactive element
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heavy water $(D _2O)$ is a compound containing deuterium and oxygen. It is used in the atomic nuclear reactor as a moderator. It differs from ordinary water $(H _2O)$ only because it has Deuterium i.e. a heavy isotope of hydrogen.