2.2 Water

After a drug's initial discovery or synthesis, the chemist then develops the drug, testing it to see if it is toxic, and then designing methods for efficient large-scale production.

The process of approving the drug for human use begins.
Drug approval in the US is handled by the FDA.
A series of largescale experiments using human subjects to ensure the drug is not harmful and effectively treats the condition for which it is intended is what this involves.
This process often takes several years and requires the participation of physicians and scientists.

An example of a drug that was discovered in a living being is an anti-cancer drug called Paclitaxel.

This drug was found in the bark of a tree.
aspirin was isolated from willow tree bark.
Hundreds of samples of plants, fungi, and other forms of life are often tested to see if they contain biologically active compounds.
Modern medicine can sometimes get clues from traditional medicine.
For thousands of years, mankind has used willow bark to make medicine.
The aspirin molecule, acetylsalicylic acid, was marketed for human use in the late 1800s.

Drug development for one use can have unforeseen effects that allow usage in other ways.

The drug minoxidil was developed to treat high blood pressure.
People taking the drug would have new hair.
The drug was marketed to men and women with hair loss.

A pharmaceutical chemist's career may include detective work, experimentation, and drug development, all with the goal of making human beings healthier.

Water is an essential part of life.

Water is the most important molecule on the planet.
70% of the human body is water.
Life as we know it would not exist without it.

Water is a unique substance with special properties that are tied to the processes of life.

Most of an organisms cellular chemistry and metabolism occur inside the watery contents of the cell's cytoplasm.
Special properties of water include its high heat capacity and heat of vaporization, its ability to ionize, and its ability to form bonds.
Understanding the characteristics of water helps to understand its importance.

The hydrogen and oxygen within water molecule form polar covalent bonds, which is one of water's important properties.

While there is no net charge to a water molecule, water's polarity creates a slightly positive charge on hydrogen and a slightly negative charge on oxygen, which contributes to water's properties of attraction.

Each water molecule attracts other water molecule because of the opposite charges between water molecule, forming hydrogen bonds.

Water attracts other polar molecule and ion.
Figure 2.13 shows that oils and fats don't interact well with water.
A good example of this is the vinaigrette and oil salad dressing.

Water and oil don't mix.

Oil does not form in water but forms droplets, as shown in the macro image.

It is a nonpolar compound.

Liquid water is important to life because of the formation of hydrogen bonds.

Understanding the chemical features of water is important since living things have a high water content.
As water moves past each other, hydrogen bonds form and break.
The bonds break due to the heat in the system.
When the heat rises as water is boiled, the water molecule's higher energy causes the hydrogen bonds to break and allow water to escape into the air.
When water temperature reduces and water freezes, the water molecule forms a structure that is less dense than liquid water because there is not enough energy to break the hydrogen bonds.

The way hydrogen bonds orient as they freeze causes water's lower density in its solid form.

Solidification when the temperature drops allows the solid to pack more tightly than in liquid form and give it a greater density.

The lower density of ice causes it to float at the surface of liquid water, such as in an ice cube in a glass of water.

In lakes and ponds, ice will form on the water's surface creating a barrier that protects the animals and plants from freezing.
Plants and animals living in the pond would not be able to survive without this ice layer.
The effect of freezing on living organisms is caused by the expansion of ice.
The ice crystals that form after freezing can irreversibly damage living cells.
Cells can only survive freezing if another liquid replaces the water in them.

Ice is less dense than liquid water because of hydrogen bonding.

The lattice structure of ice makes it less dense than liquid water, which allows it to float on water.

Water's high heat capacity is caused by hydrogen bonding among water molecule.

Specific heat is the amount of heat one gram of a substance must absorb or lose to change its temperature.
It takes a long time to heat and a long time to cool.
The heat capacity of water is five times greater than that of sand.
The land is cooler than the sea.
Warm blooded animals use water to more evenly distribute heat in their bodies, similar to a car's cooling system, because of its high heat capacity.

This change in water requires a lot of heat energy.

The water's surface is where this process occurs.
When liquid water is heating up, hydrogen bonding makes it difficult to separate the liquid water molecule from each other, which is required for it to enter its gaseous phase.
As a result, water requires more heat to boil than a liquid such as grain alcohol, whose hydrogen bonding with other alcohol molecule is weaker than water's hydrogen bonding.
As water reaches its boiling point, the heat is able to break the hydrogen bonds between the water molecule, and the motion of the water molecule allows them to escape from the liquid as a gas.

The amount of energy used in the process of breaking bonds for water to evaporate is a result of the fact that hydrogen bonds need to be broken.

As the water evaporates, energy is taken up by the process to cool the environment.
In living organisms, 90 percent of water is used to evaporate sweat so that it can maintain body temperature.

Since water is a polar molecule with slightly positive and slightly negative charges, ion and polar molecule can easily be dissolved in it.

The hydrogen bonds with water will be formed by the charges associated with these Molecules.

Dissociation occurs when atoms break off from each other.

Figure 2.15 illustrates how spheres of hydration form around the ion when we add table salt to water.
The water molecule has a partially negative charge of oxygen.
The water molecule has a partially positive charge on it.

Spheres of hydration are formed when we mix table salt with water.

The water forms a dome above the rim of the glass when it overflows.

Water is attracted to each other because of hydrogen bonding, but there is no more room in the glass.

Water droplets form on a dry surface instead of being flattened by gravity.

The paper floats on top even though it is heavier than the water.
Surface tension and cohesion keep the water molecule's hydrogen bonds intact.
It's possible to place a needle on top of a glass of water without breaking the surface tension, as shown in Figure 2.16.

The surface is pulled downward by a needle's weight.

The surface tension pulls it up, suspending it on the water's surface preventing it from sinking.

The attraction is stronger when the water is exposed to charged surfaces such as those on the inside of thin glass tubes.

The water appears to be higher on the tube's sides than in the middle, when it "climbs" up the tube placed in a glass of water.
Water is attracted to the charged glass walls of the capillary more than it is to each other and therefore sticks to it.

capillary action in a glass tube occurs when the glass' internal surface exceeds the cohesive forces between the water and the glass.

Water can be transported from the roots to the leaves with the help of cohesive and adhesive forces.

The water column is pulled by these forces.
The pull is caused by the tendency of water to evaporate on the plant's surface to stay connected to water below them.
Plants use this phenomenon to move water from their roots to their leaves.
Plants would not be able to receive the water and dissolved minerals they need without these properties of water.
The water strider uses the water's surface tension to stay afloat on the water's surface layer and even mate there, as shown in Figure 2.18.

A solution's acidity or basicity is determined by the pH of the solution.

You could have used it to test the water in the swimming pool.

The test measures the concentration of hydrogen ion in a solution.

While the hydroxide ion are kept in solution by their hydrogen bonding with other water molecule, the hydrogen ion, consisting of naked protons, immediately attract to unionized water molecule and form hydronium ion (H3O+).

Scientists refer to the concentration of hydrogen ion as if it were free in liquid water.

The H+ ion concentration in water is 1 x 10-7 moles.

A mole is a way to express the amount of a substance.
The atomic weight of a substance is expressed in grams, which equals the amount of the substance containing as many units as there are atoms in 12 grams of 12C.
One mole is equal to 1023 particles of the substance.
1 mole of water is equal to 1023 water molecule.
The negative of the base 10 logarithm is calculated as the pH.
The log10 of 1 x 10-7 has a negative number and a neutral number.
Near-neutral pH is maintained in two areas of the body where human cells and blood are found.

The dissolving acids in the water cause non-neutral pH readings.

When using the negative logarithm to generate positive integers, high concentrations of hydrogen ion yield a low pH number; whereas, low levels of hydrogen ion result in a high pH.

When the base releases hydroxide ion, these ion bind to free hydrogen ion and create new water molecule.

The stronger the acid, the easier it is to give H+.

hydrochloric acid is a highly acidic acid and tomato juice is a weak acid.
Strong bases are those substances that take up hydrogen ion.
When we place household cleaners in water, they give up OH- rapidly and raise the pH.
An example of a weak basic solution is seawater, which is close to a neutral pH that marine organisms have adapted to live and thrive in.

Anything below 7.0 is acidic, and anything above 7.0 is alkaline.

In either direction from 7.0 is inhospitable to life.
The cells' and the blood's pH is very close to neutral.
The environment in the stomach has a pH of 1 to 2.
They can't do it and are dying constantly.
New cells are created in the stomach to replace dead ones.
The stomach lining is replaced by the human body every seven to ten days.

The H+) concentration is measured on the pH scale.

You can watch this video for an explanation of the logarithmic scale.

The key is buffering.

A person's well-being is dependent on their blood pH.

When carbonic acid is combined with free hydrogen ion, it removes hydrogen ion and moderates pH changes.

Excess carbonic acid can be converted to carbon dioxide gas through the lungs.
Too many free hydrogen ion can build up in the blood and reduce the blood's pH.

If too much OH- enters the system, carbonic acid will combine with it to create bicarbonate, lowering the pH.

Without this buffer system, the body's pH would be in danger.

The body's buffering of blood pH levels is shown in this diagram.

As more CO2 is made, the blue arrows show the process of raising pH.
The reverse process is indicated by the purple arrows.

Some people use antacids to combat excess stomach acid.

Many of these over-the-counter medications work in the same way as blood buffers, usually with at least one ion capable of absorbing hydrogen and moderating pH, bringing relief to those who suffer "heartburn" after eating.
Water's unique properties that contribute to this capacity to balance pH--as well as water's other characteristics--are essential to sustaining life on Earth.