Systems and Surroundings 3.2

What is an example of adhesion?

If water is placed on glass, it will spread out instead of beading up because the adhesive forces are stronger than the cohesive forces of the individual water molecules.

What's different about water's molecular structure?

Water is a bent, v-shaped molecule because the oxygen atom has a slightly negative (ẟ-) charge while the hydrogen atoms have a slightly positive (ẟ+ ) charge. This makes water a polar molecule and attracted to other water molecules.

What are the properties of water?

Water is a polar solvent, its solid form is less dense than its liquid form, it's very cohesive and adhesive, has a strong surface tension, high specific heat capacity, and is considered a universal solvent.

"Universal" Solvent

Water is an amazing solvent, more substances dissolve in water than not but some still do.

solvent

A substance that the solute is dissolved in, and makes up the majority of the solution.

How do we identify acids and bases on the pH scale? How is pH measured?

If a solution has a pH that is > 7, then it is basic; if a solution has a pH that is < 7, it is acidic. Neutral solutions have a pH = 7. pH is a measure of the concentration of hydronium [H30+] ions. Acidic solutions (pH < 7) have more hydronium, while basic solutions (pH>7) have less hydronium.

solute

A dissolved substance that makes up the minority of the solution.

compound

A combination of 2 or more substances in which the new substance has a different chemical identity and different chemical properties from the elements it came from. This new substance is different from the elements it was created from, and its formation is a chemical change.

How is chromatography used?

Chromatography is used

In a neutral solution...

moles [H30+] = moles [OH-]

Hydrogen Bonds

water molecules stick together in these bonds, and they are responsible for most of water's properties. The positive pole around the hydrogen atoms bonds to the negative pole around the oxygen atoms of a different water molecule. This bond is weak, but gives water its properties of cohesion, which leads to surface tension.

adhesion

The attraction between 2 different substances, such as water and glass.

solutions

A mixture in which all components are in the same phase, such as all solids, liquids, or gases. This mixture is made up of 2 components, solvents and solutes.

suspensions

A mixture in which different components are in different phases, such as solid, liquid, and gases.

capillary action

A process that can uses both cohesion and adhesion to allow water to defy gravity. If you have a beaker full of water and a glass dropper, the water will adhere to the straw. Cohesion will draw other droplets into the straw, following the other water molecules. The surface tension created causes the water to climb up the straw, until gravity pulls down on the weight of the water and overwhelms the surface tension.

Why does limestone disintegrate in acid rain?

Acid rain is caused by fossil fuels, sulfur lies in coal and gets separated from the coal when burnt, it reacts with the oxygen in our air and forms Sulfur dioxide. The water and oxygen in the air react with the Sulfur dioxide to form sulfuric acid. Sulfuric acid falls to the earth in rain clouds, and corrodes the limestone, which is made up of calcium carbonate and acts as a base and accepts the H+ ions. Limestone is corroded due to the acid and base reactions that occur when the acid rain falls.

Why is water's solid form less dense than its liquid form?

At 32º F or 0º C water molecules start to solidify, and hydrogen bonds form crystalline structures which spaces molecules apart more evenly, making ice less dense than liquid water.

How are Ocean Acidification and Global Warming connected?

Both Global Warming and Ocean Acidification are caused by an increase of CO2 in the atmosphere, which is the result of people (we exhale CO2), livestock, and industry. The advantage is that both problems can be solved at once, but the disadvantage is that this is a very difficult problem.

What is an example of cohesion?

If water is placed on wax paper, teflon, or some types of plant leaves, it will adhere weakly to the surface it is placed on, but strongly to itself. The water molecules hold water drops together in a configuration that creates the least amount of surface area. This doesn't apply to all surfaces, but it does create surface tension that allows some types of bugs to walk on water.

Where does pure water stand on the pH scale?

In pure water, [H30+] = [OH-], which means water is a neutral solution and has a pH of 7

heterogeneous mixtures

Mixtures in which components are unevenly distributed, individual substances can be clearly seen with the naked eye, ex. sand in water

homogenous mixtures

Mixtures with the same composition throughout , any region of the mixture has the same ratio of substances as any other region. These mixtures can either be solutions or suspensions.

How does Ocean Acidification impact life in oceans?

Numerous organisms live in the oceans, and their lives are regulated by proteins. Proteins require a specific pH. When the ocean's pH decreases and the water becomes more acidic it results in fewer proteins for fish, causing metabolism and immunse response decreased.

What is the difference between pure and impure materials?

Pure materials consist of 1 element or compound, ex. pure copper. Impure materials are mixtures and contain 2 or more elements or compounds. "100% Pure" materials don't occur in nature, but impure materials can be purified through distillation.

How does soap remove grime?

Soap and detergent molecules are mostly non-polar, they attract grime, a non-polar molecule, via induced dipole-induced dipole attractions. (Like attracts like) Grime molecules are surrounded by and attracted to the non-polar tails of soap molecules, while the polar heads face outwards and attract polar water molecules through a semi-strong ion-dipole attraction. The flowing water washes away the grime and attached soap molecules.

What is different about the molecular structure of soaps and detergents?

Soap molecules have 2 parts, a long, non-polar tail of carbon and hydrogen atoms and a polar head that contains at least 1 ionic bond. These sections of the soap molecule give it polar and non-polar properties.

What types of acids and bases ionize completely in water?

Strong acids and bases ionize (break down into ions ) completely in water, while weak acids and bases do not ionize completely in water.

Hydrophobic (water fearing) substances

Substances that are non-polar, lack charged poles, and are not strong enough to overcome the cohesive forces of water. Water's cohesive forces push hydrophobic substances out of the water. One example is oil.

Hydrophilic (water loving) substances

Substances that are polar and dissolve in water (like dissolves like) because their polarity is stronger than the cohesive forces of water. They are strong enough to break water's cohesive forces and hydrogen bonds and causes water to bond around these polar substances. One example is salt.

cohesion

The attraction between 2 "like" things such as 2 water molecules. Water has the highest cohesion of any nonmetallic liquid.

High Heat Capacity

Water molecules are good at holding on to heat. For example, the oceans are colossal heat sinks and temperature regulators that are extremely difficult to cool down or heat up.

Hard Water

Water that contains large amounts of calcium and magnesium ions and has many undesirable properties. When heated, the Ca and Mg ions can bind to negatively charged ions and clog water heaters and boilers. This type of water also limits the actions of soaps and detergents.

What is the result of water and CO2?

When water combines with CO2, the result is carbonic acid, or H2CO3. H2CO3 quickly dissociates into bicarbonate, or HCO3-, losing a hydrogen ion in the process. From there, bicarbonate dissociates, loses another hydrogen ion, and forms carbonate. Carbonate is formed when carbonic acid loses 2 hydrogen ions and disassociates twice. The more H+ that a solution contains, the more the pH will drop and become more acidic.

Does water ionize?

Yes, in water, one H2O molecule will often lose a hydrogen to another, making one water molecule an acid and one water molecule a base. This results in the creation of 1 OH- (hydroxide) ion, and 1 H30+ (hydronium) ion, and for every hydroxide ion there is a hydronium ion, forming a neutral solution. When water is by itself, it is always neutral but it can still ionize. This process is reversible and happens constantly in water, forming a dynamic equilibrium.

Base

a chemical that accepts a H+ ion (aka proton) in a solution

Acids

a chemical that donates a H+ ion (aka proton) in a solution. These chemicals are very polar, so they don't dissolve in non-polar solutions

mixture

a combination of 2 or more substances in which each substance retains its own chemical properties and chemical identity. Most materials are mixtures.

neutralization

a reaction between an acid and a base that forms water and a salt. ex: HCI + NaOH --> H20 + NaCI (aq) HCI = acid, NaOH = base, NaCI = salt, (aq) means dissolved in water

Water is ____ and ______

amphoteric (can behave as an acid and a base) and neutral

Salt

an ionic compound formed from the reaction of a acid and a base, any elements from group 1 or group 2 (alkali metals and alkaline earth metals) and halogens.