Flashcards in Exam One Deck (22)
How did the Neolithic Revolution change people's relationship with food and one another?
The Neolithic Revolution began the transition from nomadic hunter-gatherers to civilizations and farming. Farming caused different roles in society to develop.
How did urbanization lead to food adulteration?
Urbanization separated production from consumption. Less people were making their own food so with the increase of demand and anonymity adulteration soon became very common.
What was the result of adulteration in food?
Once adulteration became more prevalent chemical tests were created in order to detect any adulteration. One example of this is the iodine test which detected starch in cream.
What is solubility dependent on?
Solubility is dependent on the electrostatic interactions between molecules. Examples of this are polar/nonpolar, positive/negative, and ionic or covalent bonding.
How is bond energy a result of electrostatic potential energy?
Bond energy is a result of electrostatic potential energy because of like/unlike charges. Like charges repel each other which means if they get closer the electrostatic potential energy will increase. Unlike charges attract each other which means if they get closer the electrostatic potential energy decreases.
What is entropy?
Entropy measures the amount of disorder or randomness. The more configurations of a system the more entropy it has. A solid has low entropy while a gas has high entropy.
What is enthalpy?
Enthalpy measures bonding energy. The stronger the bond between two molecules the lower the enthalpy.
Why does a hard crystalline fat somewhat dissolve in vegetable oil but salt crystals do not?
A hard crystalline fat and vegetable oil are non polar while salt crystals are ionic. This follows the principle of like dissolves like. Salt crystals are held together by an ionic bond which is too strong for a non polar liquid to dissolve. The two will not react.
Why can you get most things to dissolve more at higher temperatures?
At higher temperatures the molecules are moving around more which means they are more likely to react with each other. Higher temperatures lead to an increase in entropy which can make the reaction more spontaneous.
How could you measure the solubility limit of lactose in water?
To measure the solubility limit of lactose in water you can add enough lactose to a known amount of water until it becomes saturated and a sediment begins to form at the bottom. You can then let it sit until it reaches equilibrium with the air then take the saturated solution and use a refractometer to measure the amount of solute that dissolved.
How does the amount of free salt and the concentration of the solution change as you add more salt to the water?
The concentration of the solution steadily increases as you add more free salt until you reach the solubility limit which causes the concentration to plateau. The salt stops dissolving in the water. The amount of free salt is low until it reaches the solubility limit then it drastically increases.
What is a hydrogen bond and why are they so important in liquid water?
A hydrogen bond is a bond involving hydrogen and a very electronegative element such as N, O, or F. It is important in water because it is a very strong polar bond which causes it's main phase to be a liquid because the particles are packed so tightly.
Which bonds are made and which bonds are broken when salt dissolves in water?
The bonds that are made are hydrogen and the anion and oxygen and the cation. The bonds that are broken are those between the anion and cation. The water molecules orient themselves around the ions.
What is a polar molecule and how does it react with water?
A polar molecule has a net dipole as a result of opposing charges. These dipoles interact with water's dipoles which causes the molecule to dissociate in the water. These dipole dipole moments cause the substance to dissolve.
What is the basis for hydrophobic attractions between non polar molecules dissolved in water?
Non polar molecules are hydrophobic which means they do not dissolve in water this is because they have no dipoles or ionic bonds to interact with. Non polar molecules have transient dipoles which means it always has a neutral charge.
Describe a clathrate cage.
A clathrate cage is an assortment of water molecules orienting themselves around a non polar molecule. The water is only slightly attracted to the non polar molecule so it tries to interact with it as little as possible. The clathrate cage decreases the system's entropy.
How does the hydrophobic effect control the behavior of surfactants and membranes?
The hydrophobic effect dictates that the substance will not dissolve in water. This means that the non polar molecules will float together on top of the water creating a surfactant.
What is lecithin?
Lecithin is an emulsifier that contains mainly phospholipids which are amphiphilic. As a result it is able to react with the non polar and polar substances. This creates a stable heterogenous mixture.
What is pH?
pH is the measure of the negative log of the concentration of hydrogen ion in a solution.
What is pKa?
pKa is the acid equilibrium constant.
What is water activity and how is it controlled?
Water activity is the amount of free water in a substance. It is controlled by the addition of a solute (sugar,salt), dehydration/evaporation, adding a water binding polysaccharide (pectin).