College Chemistry : Properties of Water

Study concepts, example questions & explanations for College Chemistry

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Example Questions

Example Question #1 : Properties Of Water

Which of the following is not true about water?

Possible Answers:

Its solid form is more dense than its liquid form

It's molecular geometry is bent

It participates in many biochemical reactions

It has a high heat capacity relative to other solvents

Its ability to make hydrogen bonds with other water molecules allows for great cohesion

Correct answer:

Its solid form is more dense than its liquid form

Explanation:

Unlike most other solvents, water is unique in that its solid form is actually less dense than its liquid form. This is precisely the reason why ice floats in water. Water does indeed participate in many biochemical reactions and can form hydrogen bonds with other water molecules to allow for great cohesion. Also, the specific heat capacity of water is , which is the amount of heat required to raise the temperature of one mole of substance by 1 Kelvin. This value is much higher than the specific heat capacities of many other solvents. For example, the specific heat capacity for hexane is .

Example Question #2 : Properties Of Water

The unique properties of water, namely its incredibly high heat capacity and surface tension, can be attributed to which of the following kinds of intermolecular/intramolecular forces?

Possible Answers:

All of these

London dispersion forces

Van der Waals forces

Ionic bonding

Hydrogen bonding

Correct answer:

Hydrogen bonding

Explanation:

The partial negative and positive charges on a water molecule allow it to be attracted to other polar water molecules, which creates the cohesive nature of water and contributes to its high surface tension and heat capacity. London dispersion and Van der Waals forces are significantly weaker than hydrogen bonding. Additionally, ionic bonding only occurs intramolecularly, so it has little effect on the intermolecular properties of water.

Example Question #3 : Properties Of Water

Is water an acid or a base?

Possible Answers:

Acid

Neither

Base

Both

Correct answer:

Both

Explanation:

Water is an amphipathic molecule, meaning that it can act as both an acid and a base. In some situations, water can act as a Bronsted-Lowry base (defined as a species which accepts a proton). Here is an example of water acting as a base:

As you can see,  accepted a hydrogen atom (proton) to become .

In other situations, water can act as a Bronsted-Lowry base (defined as a species which donates a proton). Here is an example of water acting as an acid:

As you can see,  donated a hydrogen atom (proton) to become .

Thus, water can act as both an acid and a base. 

Example Question #4 : Properties Of Water

Which of the following substances is the least soluble in water?

Possible Answers:

Correct answer:

Explanation:

 (benzene) is the least soluble in water because it is a non polar substance. Polar compounds are soluble in water because like dissolves like. Water is polar and therefore dissolves other polar substances. The more polar or ionic a substance is, the more soluble it is in water.  are polar compounds because of the uneven electron distribution within these compounds.

Example Question #5 : Properties Of Water

Water is said to be the solvent of life due to its very unique properties. Which of the following does not represent one of the features of water that gives it uniqueness?

Possible Answers:

Formation of hydrogen bonds

High heat capacity

All of these represent unique characteristics of water

Low surface tension

Liquid phase that is more dense that the solid phase

Correct answer:

Low surface tension

Explanation:

In this question, we're asked to identify an answer choice that describes something that is not a characteristic of water.

Remember that water molecules consist of a single oxygen atom with single bonds to two hydrogen atoms. There are also two lone pairs of electrons on the oxygen atom, giving the overall molecular structure of water a bent shape. This bent shape is important, because it results in an overall net dipole moment of the water molecule, where the two hydrogen atoms have a partial positive charge and the oxygen atom has a partial negative charge.

The significance of this partial charge separation is that it allows water to be excellent at forming hydrogen bonds. Recall that hydrogen bonds occur when a partially positive hydrogen atom participates in a non-covalent bond to another electronegative atom on some other molecule (though can also be intramolecular in bigger compounds, like enzymes). These intermolecular interactions between individual water molecules results in an overall strong force of attraction between them.

As a consequence of these strong hydrogen bonds between the water molecules, many unique properties of water result. For instance, liquid water has an unusually high heat capacity. Due to the strong intermolecular forces of attraction, it takes a relatively large amount of energy in order overcome the attractive forces that hold water molecules together. Another very unique property of water is that its solid phase is actually less dense than its liquid phase. Thus, when water freezes into ice, it will float to the top surface in a body of water, which is important for sustaining life in certain environments.

Finally, these strong intermolecular hydrogen bonds give water a high surface tension. Once again, the reason for this is due to the fact that it takes a relatively greater amount of energy in order to break these bonds apart. Thus, water does not have low surface tension, making this the correct choice.

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