Video Transcript
Which of the following is not a
property of water? (A) Having a chemical formula of
H2O. (B) Having a relatively high
boiling point. (C) Having a lower density when
frozen. (D) Having ionic molecules. Or (E) being a good polar
solvent.
This question is asking us to
identify the statement that does not describe a property of water. Let’s have a look at our answer
choices.
Answer choice (A) describes water
as having a chemical formula of H2O. Water is a compound with the
formula H2O. This means each molecule of water
contains one oxygen atom and two hydrogen atoms. Since this is a true statement, we
can eliminate answer choice (A).
Answer choice (B) suggests that
water has a relatively high boiling point. Water melts at zero degrees Celsius
and boils at 100 degrees Celsius. We can compare this to another
molecule that is similar to water, such as hydrogen sulfide. Even though it is similar in size
and structure to water, hydrogen sulfide melts at negative 82 degrees Celsius and
boils at negative 60 degrees Celsius. Relative to molecules like it, the
melting and boiling points of water are high. Since this is true, we can
eliminate answer choice (B).
Answer choice (C) suggests that
water has a lower density when frozen. Water molecules are polar
molecules. Polar molecules are covalently
bonded molecules with partially negative sides and partially positive sides. The negative side of the molecule
can be labeled using a 𝛿 minus symbol, while the positive side of the molecule can
be labeled using the 𝛿 plus symbol. Polar water molecules are able to
engage in a special type of interaction called hydrogen bonding.
Hydrogen bonding is a strong
attraction between hydrogen atoms and the negative ends of adjacent molecules. The diagram represents the hydrogen
bonding occurring between separate water molecules using green dotted lines. In the liquid state, water
molecules engage in hydrogen bonding that forms a relatively random and close
arrangement. When the temperature drops and the
liquid water begins to freeze, a new arrangement occurs. As a solid, water molecules form a
hexagonal pattern that takes up more space than the arrangement as a liquid. The same mass of water when frozen
has a greater volume. This causes ice to have a lower
density than liquid water. This is the reason why ice floats
on water. Since a lower density when frozen
as a solid is a property of water, we can eliminate answer choice (C).
Answer choice (D) suggests that a
property of water is having ionic molecules. Water molecules are polar covalent
molecules, which have partial charges. They are partially charged, not
completely charged. Additionally, particles that are
completely charged are called ions, not ionic molecules. Since this statement is not a
property of water, this is the correct answer to this question. Let’s have a look at answer choice
(E) just to be sure.
Answer choice (E) suggests that a
property of water is being a good polar solvent, which means it can dissolve other
polar compounds. Since water is a polar molecule, as
a solvent, it is a polar solvent and can dissolve many other polar and ionic
compounds. For example, we can add sugar to
water. And both water and sugar are
polar. When sugar is added to water, it
dissolves readily. Therefore, water is a good polar
solvent. And thus, answer choice (E) can be
eliminated.
So, the statement that is not a
property of water is answer choice (D): having ionic molecules.
