2.2: Water

*Write the molecular formula for water.* Understanding: Water molecules are polar and hydrogen bonds form between them.

Water is *H2O*

*State if the following molecule is hydrophobic or hydrophilic: cholesterol.* Application: Modes of transport of glucose, amino acids, cholesterol, fats. oxygen, and sodium in blood in relations to their solubility in water.

*Hydrophobic* Cholesterol is primarily a non-polar hydrocarbon and does not form hydrogen bonds with water.

*State if the following molecule is hydrophobic or hydrophilic: fats.* Application: Modes of transport of glucose, amino acids, cholesterol, fats. oxygen, and sodium in blood in relations to their solubility in water.

*Hydrophobic* Fats are primarily non-polar hydrocarbons and do not form hydrogen bonds with water.

*Define anion.* Understanding: Water molecules are polar and hydrogen bonds form between them.

A *negatively charged ion* because it has gained electrons

*Define cation.* Understanding: Water molecules are polar and hydrogen bonds form between them.

A *positively charged ion* because it has lost electrons.

*State if the following molecule is hydrophobic or hydrophilic: amino acids.* Application: Modes of transport of glucose, amino acids, cholesterol, fats. oxygen, and sodium in blood in relations to their solubility in water.

*Generally* Hydrophilic Although variable, many amino acids have polar or ionic "R" groups which are able to form hydrogen bonds with water.

*State if the following molecule is hydrophobic or hydrophilic: glucose.* Application: Modes of transport of glucose, amino acids, cholesterol, fats. oxygen, and sodium in blood in relations to their solubility in water.

*Hydrophilic* Glucose has many polar -OH groups which are able to form hydrogen bonds with water.

*State if the following molecule is hydrophobic or hydrophilic: sodium chloride.* Application: Modes of transport of glucose, amino acids, cholesterol, fats. oxygen, and sodium in blood in relations to their solubility in water.

*Hydrophilic* The ions are able to dissolve in water.

*Compare the physical properties of methane and water.* Application: Comparison of the thermal properties of water with those of methane.

*Methane (CH4)* Gas at room temperature Lower heat capacity *Water (H2O)* Liquid at room temperature Higher heat capacity (more energy to change temp)

*Explain why water and methane have different thermal properties based on their molecular structures.* Application: Comparison of the thermal properties of water with those of methane.

*Methane is nonpolar* whereas *water is polar*. Because water is polar, it is able to form hydrogen bonds with many types of molecules. As a nonpolar molecule, methane does not form hydrogen bonds with other molecules.

*List types of molecules that are hydrophobic.* Understandinding: Substances can be hydrophilic or hydrophobic.

*Nonpolar* or *non-ionic* molecules are hydrophobic.

*Define "polar" in relation to chemical bonding.* Understanding: Water molecules are polar and hydrogen bonds form between them.

*Polar* means a molecule has regions of slight charge due to the unequal sharing of electrons in a polar covalent bond. One of the atoms has more of a tug on the electrons that another, making it slightly negatively charged.

*Define hydrophobic.* Understandinding: Substances can be hydrophilic or hydrophobic.

A molecule or substance that is *NOT attracted to water*.

*Define hydrophilic.* Understandinding: Substances can be hydrophilic or hydrophobic.

A molecule or substance that is *attracted to water*.

*State why scientists cannot prove without a doubt that hydrogen bonds exist between water molecules.* Nature of Science: Use of theories to explain natural phenomena- the theory that hydrogen bonds form between water molecules explain the properties of water.

A scientific theory is a *well supported explanation* of some aspect of the natural world that is supported through repeated observation and experimentation. Because H-bonds have yet to be directly observed, their presence can not be proven, however H-bonding does mathematically, chemically and observationally explain the properties of water.

*Outline an example of the adhesive property of water being of benefit to life.* Understanding: Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.

Adhesion is needed for *water to move from the roots to the leaves* of plants. Water sticks to the sides of the xylem wall through adhesion.

*Contrast covalent, ionic and hydrogen bonds.* Understanding: Water molecules are polar and hydrogen bonds form between them.

All bonding involves electrons or the charges that result from the giving/taking of electrons. *Covalent bond*: electrons are shared between two atoms *Ionic bond*: attraction between cation and anion (no sharing of electrons) *Hydrogen bond*: an attraction (not a true bond) between two polar molecules.

*Describe the structure of an atom.* Understanding: Water molecules are polar and hydrogen bonds form between them.

Atoms are composed of *protons*, *neutrons* and *electrons*. Protons have a positive charge, neutrons have no charge and electrons have a negative charge. Protons and neutrons are found in the atomic nucleus. Electrons are found in a cloud surrounding the nucleus.

*Outline the mechanism of transport of glucose in the blood.* Application: Modes of transport of glucose, amino acids, cholesterol, fats. oxygen, and sodium in blood in relations to their solubility in water.

Blood is primarily water. Because it is hydrophilic, glucose *can dissolve and be directly transported* in the blood.

*Outline the mechanism of transport of cholesterol in the blood.* Application: Modes of transport of glucose, amino acids, cholesterol, fats. oxygen, and sodium in blood in relations to their solubility in water.

Blood is primarily water. Because it is hydrophobic, cholesterol must be transported in the blood within "sacs" called lipoproteins. Lipoproteins are a group of soluble proteins that combine with and transport fat or other lipids in the blood plasma.

*Outline the mechanism of transport of fats in the blood.* Application: Modes of transport of glucose, amino acids, cholesterol, fats. oxygen, and sodium in blood in relations to their solubility in water.

Blood is primarily water. Because it is hydrophobic, fats must be transported in the blood within "sacs" called lipoproteins. Lipoproteins are a group of soluble proteins that combine with and transport fat or other lipids in the blood plasma.

*Outline the mechanism of transport of amino acids in the blood.* Application: Modes of transport of glucose, amino acids, cholesterol, fats. oxygen, and sodium in blood in relations to their solubility in water.

Blood is primarily water. Because most are hydrophilic, amino acids can usually *dissolve and be directly transported* in the blood.

*Outline the mechanism of transport of sodium chloride in the blood.* Application: Modes of transport of glucose, amino acids, cholesterol, fats. oxygen, and sodium in blood in relations to their solubility in water.

Blood is primarily water. Because they are hydrophilic. sodium and chloride ions can *dissolve and be directly transported* in the blood.

*State if the following molecule is hydrophobic or hydrophilic: oxygen.* Application: Modes of transport of glucose, amino acids, cholesterol, fats. oxygen, and sodium in blood in relations to their solubility in water.

Gaseous oxygen does not react with water. It is water soluble depending on temperature and pressure conditions.

*Given a diagram of a molecular structure, determine if the molecule is hydrophilic or hydrophobic: HYDROCARBONS.* Understandinding: Substances can be hydrophilic or hydrophobic.

If there are no charges and no polar covalent bonds, then water will not be attracted, making the molecule hydrophobic.

*Describe the cause and effect of the polar nature of water.* Understanding: Water molecules are polar and hydrogen bonds form between them.

In water, the oxygen has a greater "pull" on the shared electrons than the hydrogen atoms. As a result, there is unequal sharing of the electrons, with the electrons drawn closer to the oxygen. As a result, the oxygen has a slightly negative charge and the hydrogens have a slightly positive charge.

*Outline a benefit to life of water's high latent heat of vaporization.* Understanding: Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.

It takes a relatively high amount of heat energy to vaporize water (convert from liquid to gas) because hydrogen bonds must be broken. As the water evaporates, the surface it leaves becomes cooler. This is called *evaporative cooling* and allows organisms to cool with sweating.

*Outline a benefit to life of water's high specific heat capacity.* Understanding: Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.

It takes a relatively large amount of heat energy to raise the temperature of water. This is a benefit because the temperature of large bodies of water remains relatively constant, protecting life from potentially lethal temperature fluctuations.

*Outline the mechanism of transport of oxygen in the blood.* Application: Modes of transport of glucose, amino acids, cholesterol, fats. oxygen, and sodium in blood in relations to their solubility in water.

Oxygen is transported in the blood by binding to a protein transport molecule (hemoglobin) within the red blood cells.

*Explain sweating as a mechanism to cool the body.* Application: Use of water as a coolant in sweat.

Sweat is mostly water. When the water evaporates from the surface of the skin, it takes heat with it. With the loss of the heat energy, the skin feels cooler.

*Given a diagram of a molecular structure, determine if the molecule is hydrophilic or hydrophobic: PHOSPHATE GROUP.* Understandinding: Substances can be hydrophilic or hydrophobic.

The negative charge found on a phosphate group makes it an ION. Water is attracted to ions, making them hydrophilic.

*Given a diagram of a molecular structure, determine if the molecule is hydrophilic or hydrophobic: HYDROXYL GROUP.* Understandinding: Substances can be hydrophilic or hydrophobic.

There is a *polar* covalent bond between the O and H in a hydroxyl group. As a result, water is attracted, making molecules with many hydroxyl groups hydrophilic (such as glucose).

*Outline a benefit to life of water's high boiling point.* Understanding: Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.

Water boils at a relatively high temperature for a compound made of such light elements; this is due to the hydrogen bonding between water molecules causing them to resist being pulled apart (which is what happens when water boils to become a gas). Without this, water would not be a liquid over much of the surface of the Earth and we would not have a liquid ocea.

*Outline an example of the cohesive property of water being of benefit to life.* Understanding: Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.

Water cohesion allows for *surface tension*, allowing some insects to stay on the surface of the water. Water cohesion creates a chain of water molecules that allows for the *transport of water from the roots to the leaves* of plants. Water cohesion is responsible for the *high heat capacity* of water, maintaining a relatively stable internal temperature and external environment for living organisms.

*Describe where and how water is able to form hydrogen bonds.​* Understanding: Water molecules are polar and hydrogen bonds form between them.

Water forms hydrogen bonds between the *partial positive hydrogen of one water molecule and the partial negative oxygen of ANOTHER water molecule*. One water molecule is capable of forming up to four hydrogen bonds with other water molecules.

*Explain why is water such a good solvent.* Understanding: Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.

Water is a good solvent because it can form hydrogen bonds with a variety of different substances. Water is called the "universal solvent" because it dissolves more substances than any other liquid.

*List types of molecules that are hydrophilic.* Understandinding: Substances can be hydrophilic or hydrophobic.

Water is a polar molecule that attracts other *polar* or *ionic* substances, making them hydrophilic.

*Define cohesion.* Understanding: Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.

Water molecules *attaching to other water molecules* through hydrogen bonding.

*Define adhesion.* Understanding: Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.

Water molecules *bonding to non-water molecules* through hydrogen bonding or attraction to an ionic charge.

*List the types of molecules that water will dissolve.​* Understanding: Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.

Water will dissolve substances that are polar or ionically charged.

*Contrast ion with atom.* Understanding: Water molecules are polar and hydrogen bonds form between them.

*Atoms* have no net charge because the have equal numbers of protons (+) and electrons (-). If an atom gains or loses an electron it will have a net charge and be called an *ion*.