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Culinary Chemistry > Quiz #2 > Flashcards

Quiz #2 Flashcards

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1
Q

Name the different kinds of bonds.

A

Ionic, non-polar covalent, polar covalent, and hydrogen bonds.

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2
Q

How do bonds occur?

A

Stability (if there is an unpaired electron in the outer shell, it is not stable, atoms want to be stable)

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3
Q

What are ionic bonds and how do they form?

A

This chemical bond involves a transfer of an electron, so one atom gains an electron while one atom loses an electron. One of the resulting ions carries a negative charge (anion), and the other ion carries a positive charge (cation). Because opposite charges attract, the atoms bond together to form a molecule, occurs in very rigid and strong solids - metals and salts, “taken, not shared”.

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4
Q

What are covalent bonds and how do they form?

A

The most common bond in organic molecules, a covalent bond involves the sharing of electrons between two atoms. The pair of shared electrons forms a new orbit that extends around the nuclei of both atoms, producing a molecule. Covalent bonds often form between similar atoms, nonmetal to nonmetal or metal to metal. Covalent bonding signals a complete sharing of electrons. There is usually a direct correlation between positive and negative ions, meaning that because they share electrons, the atoms balance. Covalent bonds are usually strong because of this direct bonding.

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5
Q

What are polar covalent bonds and how do they form?

A

Two atoms connected by a covalent bond may exert different attractions for the electrons in the bond, producing an unevenly distributed charge, one end of the molecule slightly negatively charged and the other end slightly positively charged. Polar covalent bonds often indicate polar molecules, which are likely to bond with other polar molecules but are unlikely to bond with non-polar molecules. (UNEQUAL SHARING OF ELECTRONS)

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6
Q

What are hydrogen bonds and how do they form?

A

Hydrogen bonds only form between hydrogen and oxygen (O), nitrogen (N) or fluorine (F). Hydrogen bonds are very specific and lead to certain molecules having special properties due to these types of bonds. Hydrogen bonding sometimes results in the element that is not hydrogen (oxygen, for example) having a lone pair of electrons on the atom, making it polar. Lone pairs of electrons are non-bonding electrons that sit in twos (pairs) on the central atom of the compound. Water, for example, exhibits hydrogen bonding and polarity as a result of the bonding.

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7
Q

What are non-polar covalent bonds and how do they form?

A

(EQUAL SHARING OF ELECTRONS) Completely neutral, similar electronegativities so there is an equal pull on electrons, resulting in no partial charges like there are in polar covalent bonds.

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8
Q

What are condensation reactions?

A

“Dehydration synthesis”, water coming out to pull two molecules together. Used to build biological polymers, need an H and an OH group on monomers, water forms.

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9
Q

What are polymers?

A

Long chains of individual units (monomers), proteins, nucleic acids, polysaccharides.

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10
Q

What are hydrolysis reactions?

A

Using water to split apart molecules, used to break polymers, water necessary.

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11
Q

What is an isomer?

A

Something with the same molecular formula but a different molecular structure.

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12
Q

Why are fats that can be easily stacked more stable?

A

They’re more solid because less entropy.

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13
Q

Why do trans fats stack easier than cis fats do?

A

In cis unsaturated fats, the hydrogen is bound in the same orientation as the hydrogen on the other end of the carbon-carbon double bond. Trans fats, due to relatively linear shape when compared to other unsaturated fats, are able to bundle together and stack. Stacked trans fats are extremely stable and have much higher melting point than the corresponding cis unsaturated fat.

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14
Q

What is steric?

A

The shape of something.

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15
Q

What is the main importance of chemical interactions?

A

Holds molecules together.

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16
Q

WHAT IS THE REASON FOR LIFE ITSELF?

A

HYDROGEN BONDS.

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17
Q

What is hydrogen bonding?

A

Attraction between partial positive and partial negative atoms involved in a polar covalent bond. Not a permanent physical bond, like covalent, but a weak electrical attraction. Weakest after London Forces.

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18
Q

What is cohesion?

A

Water bonding to each other.

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19
Q

What is adhesion?

A

Water bonding to something else (ex: holding your finger on one end of a straw).

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20
Q

What are London Forces?

A

Interactions between hydrophobic compounds, due to short-lived electrical imbalances, weak, shape important, (single electron jumping from one fat to another, this creates this intermolecular force). WEAKEST!

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21
Q

What is charge repulsion?

A

It forces molecules to be away from each other, keeps them from making contact. Charges can be neutralized, which stops repulsion. Ion bridges = Putting a negative in between two positive things, forming an ionic bridge.

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22
Q

What are steric effects?

A

Shape effects, shape affects how much two molecules can make contact and therefore associate with one another.

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23
Q

What are stereoisomers?

A

Same shape but mirror images.

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24
Q

What are summation effects?

A

All molecules have a myriad of forces acting within (and between) them. Behavior of a molecule is determined by the sum of these effects.

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25
What is macromolecule behavior?
Behavior of the food in the kitchen largely due to the behavior of macromolecules. Techniques can be manipulated to get to desired end products (ex: changing the shape of albumin by heat, shape then changes the composition of the egg) ((denaturing protein)).
26
Why is using oil to cook meat beneficial?
High temperature, less time, cooks thoroughly, easier to get a better outcome this way.
27
What is happening when making ceviche molecularly?
Denaturing with an acid, H+ ions breaking apart bonds, attacking them and changing the shape of it, making it okay for us to eat; H+ ions are bonding and affecting the protein structure.
28
What is happening in jellies molecularly?
Protein molecules are meshing together and forming bonds, while this is occurring, water and other particles are getting trapped in the matrix and become immobile.
29
What is happening in brining?
Pulling water out (osmosis) and then salt breaks apart cell membranes, and then the liquid seeps back in and diffuses.
30
What does the reaction rate depend on?
The concentration of the "limiting reactant", temperature and pH dependent ex: having one pound of cheese, five pounds of ham and ten pounds of bread, the limiting reactant is the one pound of cheese. Most reactions have enzymes to speed up their reactions rate.
31
What is equilibrium determined by?
The relative energies of the reactants and products.
32
What is activation energy?
Energy needed to form the activated complex.
33
Temperature effects on chemical reactions?
High temperatures speed reactions, low temperatures will slow them down.
34
pH effects on chemical reactions?
Some reactions require an addition or removal of a proton (H+), such as ceviche.
35
What are catalysts?
Speed reactions without being consumed by lowering the activation energy requirement. Meaning more collisions have the necessary energy.
36
What are enzymes?
Protein catalysts, reduces the amount of energy to get a reaction started.
37
What is a substrate?
A reactant that an enzyme works upon.
38
All enzymes are catalysts -
but not all catalysts are enzymes.
39
What is stoichiometry?
"Balancing equations", relative proportions of reactants and products.
40
What is the composition of water?
One mole of oxygen to two moles of hydrogen, bent shape, only two covalent bonds and they are both polar (a mickey head, the middle is a negative oxygen, and the ears are two positive hydrogens).
41
What does molecular motion mean?
Atoms and molecules are constantly moving around, never stay in one spot, rotation and vibration as well also occur.
42
What is ionization?
One H breaks apart and becomes either an H+ or an H-. Oxygen pulls on one of them, then the other can dissociate and it's free floating now.
43
Explain a liquid water structure vs an ice structure.
A liquid structure is going to be denser and more organized than the ice's structure will be, this is why ice floats in water because it is less dense.
44
What is surface tension?
Hydrogen bonds taking the weight of something (fly on water example) and they disperse it. The fly is standing on the water because of surface tension.
45
What is heat capacity?
How much heat energy something can hold before going to another phase, water is not a good conductor but it has a high heat capacity, whereas copper conducts really well but it has a low heat capacity.
46
Why can't we use certain fruits to make gelatin? (proteases)
The proteases found in these fruits cut the gelatin's proteins into such small pieces that they are no longer able to tangle together and create a semisolid structure.
47
What does temperature do and how does it affect polyphenol oxidases?
If you raise the temperature of the environment in which a banana is, polyphenol oxidase (decompose) will occur even faster as the heat and increased moisture in the air encourages bacteria and mold growth and increases the rate of natural food enzyme reactions. If you put it in the freezer, you're stopping the movement of water, therefore it will slow this process down.
48
Why do certain fruits brown after you cut them?
The cells of apples and other produce (e.g., pears, bananas, peaches, potatoes) contain an enzyme (called polyphenol oxidase or tyrosinase) that, when in contact with oxygen, catalyzes one step of the biochemical conversion of plant phenolic compounds to brown pigments known as melanins. You see the browning when the fruit is cut or bruised because these actions damage the cells in the fruit, allowing oxygen in the air to react with the enzyme and other chemicals.
49
What are all the different ways of slowing down polyphenol oxidase?
By inactivating the enzyme with heat (cooking), reducing the pH on the surface of the fruit (by adding lemon juice or another acids), reducing the reaction rate by storing the fruit in the refrigerator, reducing the amount of available oxygen (by putting cut fruit under water or vacuum packing it), or by adding certain preservative chemicals (like sulfur dioxide).
50
Would pectin gel be affected by proteases?
Pectin needs partners, namely acid and sugar, to do the job of gelling properly. Acid helps extract pectin from fruit during gentle simmering and helps the gelling process. Because there is acid present, this shouldn't occur at the same rate, I believe it would happen over a longer period of time. This is why jellies have a small amount of liquid at the top when haven't been used for a while. ???
51
Why did browning occur more at 40 degrees C?
Because this is the temperature where most bacteria develop rapidly.
52
Rock candy? Explain pls.
As time passes, the water will evaporate slowly from the solution. As the water evaporates, the solution becomes more saturated and sugar molecules will continue to come out of the solution and collect on the seed crystals on the string.
53
What's the purpose of the string in the rock candy experiment?
The string will provide the surface on which the crystals will grow. As water evaporates from the string, small crystals of sugar will encrust the string. These tiny seed crystals provide starting points for larger crystals.
54
What effect does corn syrup have on a sugar solution and why?
Corn syrup is primarily glucose, glucose molecules are smaller than sucrose (table sugar) and can impair crystallization by coming between the sucrose molecules, ultimately interfering with crystal formation (invert sugar works the same way, etc, etc.).
55
If you added alcohol to the rock candy recipe what would happen?
If you add alcohol (ethanol or methanol) to water, sucrose becomes less soluble in the solvent mixture which should cause it to crystallize more readily.
56
What happens when adding an acid to the rock candy recipe solution?
If you add propionic acid to water, sucrose also becomes less soluble which should cause it to crystallize more readily. However, having extra molecules in the solution could affect how easily sucrose molecules can reach a crystal surface to add to it, which may slow down crystallization.
57
How would you make a candy that has smaller sugar crystals?
By letting the fudge cool without stirring, you avoid creating seed crystals. Stirring would help sucrose molecules "find" one another and start forming crystals. Stirring also introduces air, dust, and small dried bits from the walls of the saucepan—all potential seeds for crystal formation. When the fudge has cooled to about 110° F, you want to start the crystallization process. You start to stir and keep stirring until the candy becomes thick. The more you stir, the more crystal seeds you get. But instead of getting a few huge crystals (and grainy candy), you get lots and lots of tiny crystals, which make for thick, smooth candy.
58
Explain the differences between using butter and shortening in a recipe.
Butter has a lower melting point than shortening or margarine, causing it to spread more during baking, resulting in a thinner cookie or biscuit. There is a lot more moisture to fat in shortening, therefore more air pockets will form, resulting in a higher product.
59
What is shortening and what does it do?
Shortening is a type of solid fat that is made from vegetable oils, such as soybean and cottonseed oil. Shortening seems to get its name from the fact that it shortens gluten strands in wheat by adding fat.
60
What's the difference between homogeneous and heterogeneous matter?
In foods that are homogeneous, individual components cannot be visually discerned. Solutions, such as some beverages, are examples of homogeneous matter', in which one substance is dissolved into another. In heterogeneous matter, individual components can be visually discerned and may be distributed unevenly.
61
What is solubility?
The maximum amount of solute that dissolves in a specified volume of solvent at a specified temperature.
62
What is a reaction?
A chemical reaction is a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products. (Start with reactants, finish with products.)
63
What is reaction rate?
Reaction rate is the speed at which a chemical reaction proceeds. It is often expressed in terms of either the concentration (amount per unit volume) of a product that is formed in a unit of time or the concentration of a reactant that is consumed in a unit of time.
64
What is a catalyst?
A catalyst is a substance that speeds up a chemical reaction, but is not consumed by the reaction; hence a catalyst can be recovered chemically unchanged at the end of the reaction it has been used to speed up, or catalyze.
65
What is stoichiometry?
The relationship between the relative quantities of substances taking part in a reaction or forming a compound, typically a ratio of whole integers.
66
How does a refractometer work?
Amount of solutes in the substance are what the light refracts off of, how much this light bounces off of the sugar solutes is then measured in Brix.
67
What kind of bonds would be hydrophobic?
Polar covalent bonds.
68
What's the difference between a suspension and a colloid?
Colloids too large to dissolve, too small to come out. Suspension is unstable, has large particles that will come out and settle at the bottom most likely. Suspension will settle out, colloids will not.
69
How do you stabilize a colloid?
An emulsifier or mechanical (agitation).
70
What is a nucleation site?
This is where phase change is going to occur, the seeds on the stick in the crystal experiment were the nucleation sites and this is the point where they will grow and continue to grow off of.
71
What is a buffer?
Something that can resist change in pH/prevent them from occurring.
72
What is pectin?
It is a carbohydrate, found in the cell walls in a cell, it is the cement that holds cellulose together in the cell walls. A calcium salt needs to be added to form a gel because this is necessary in the formation of ionic bridges.
73
What is pectin?
It is a carbohydrate, found in the cell walls in a cell, it is the cement that holds cellulose together in the cell walls. A calcium salt needs to be added to form a gel because this is necessary in the formation of ionic bridges.
74
What is matter?
Any substance with mass and volume.
75
What are atoms?
Basic building blocks of matter that have a small, dense nucleus surrounded by an electron cloud.
76
Atomic mass =
Proton mass and neutron mass.
77
Atomic number =
Number of protons.
78
Describe electrons
Negative charge, small, fast-moving, location is based on energy and probability.
79
What determines the atomic charge?
The balance between protons and electrons. If you add or remove electrons, you get ions.
80
What are molecules?
Groups of atoms that are bound by different forces.
81
What are elements?
Pure substance of only one kind of atom.
82
What is mass and how is it measured?
How much "stuff" is in something. Using a balance or scale - grams.
83
What is volume and how is it measured?
How much space is taken up by "stuff". Using graduated containers - liters.
84
What is concentration and how is it measured?
The proportion of solute to solvent. Using electrochemical meters or refractometers - g/l, g/kg, % etc.
85
What is temperature and how is it measured?
The average movement/speed per molecule. Using a thermometer, thermocouple, etc. - degrees.
86
What is composition and how is it measured?
Nutrient composition is determined by separation. Using chromatography - concentration units.
87
What is reaction rate and how is it measured?
Indicators show rates of reaction, such as a change in absorbance, etc. - change/time.
88
What is rheology and how is it measured?
How things flow/move. Measured using a bostwick, viscometers, rheometers, etc. - poise.
89
What is optics and how is it measured?
Interaction with light. Measured using a spectrophotometer, colorimeter - absorbance units.
90
What is texture and how is it measured?
Various physical properties. Measured using a texture analyzer or durometer - newtons.
91
What is osmosis?
The movement of water across membranes. Water moves from areas with few solutes to areas with more until concentration equalizes.
92
What is electronegativity?
The "hunger" for electrons, different for different atoms, periodic trend.
93
How can you determine the amount of valence electrons by just looking at the periodic table?
By looking at the period number.
94
Entropy
The amount of disorder in a system.
95
Hydronium ion vs hydroxide ion?
``` H2O = Hydronium ion OH- = Hydroxide ion ```
96
What is ionization?
When a hydrogen can turn into an H+ or OH-
97
What is adhesion?
Bonding to other things
98
What is cohesion?
Bonding to each other
99
What is the summation effect?
All molecules have a myraid of forces acting within and between them, the behavior of molecules is determined by the sum of these effects.
100
What is steric?
Shape affects how much two molecules can make contact and therefore associate with one another.
101
What is charge repulsion?
Keeps molecules from making contact, charges can be neutralized which stops repulsion and this can be done by ionic bridges.
102
What are London Forces?
A type of force acting between atoms and molecules. They are weak intermolecular forces arising from quantum induced instantaneous polarization multipoles in molecules (interactions between hydrophobic compounds). Due to short lived electrical imbalances. Very weak.
103
What is a hydrogen bond?
An electrostatic attraction between two polar groups that occurs when a hydrogen atom covalently bound to a highly electronegative atom such as nitrogen, oxygen or fluorine. Partial positive and partial negative atoms involved in a polar covalent bond. Weak electrical attraction.
104
Unsaturated fats?
CIS vs TRANS Cis: Staying on one side Trans: "Through" from one side to another
105
Isomers?
Same formula, different structure.
106
Enthalpy?
The amount of heat energy going in or out of a system. More enthalpy = more entropy.
107
How do you make or break bonds?
Energy input, proximity, orientation, concentration, energy of activation.
108
Isotonic?
Relating to a solution having the same osmotic pressure as some other solutions.
109
Hypotonic?
Lower osmotic pressure than a particular fluid.
110
Hypertonic?
Higher osmotic pressure than a particular fluid.
111
Osmotic pressure?
Pressure that is created by osmosis (movement of water).
112
Solvent vs solute?
Solvent: H2O Solute: Whatever goes in the mixture.
113
Diffusion?
Particles will move from a high concentration to a low concentration until equilibrium is reached.
114
What does reductive mean?
Looking at a specific component from the system.
115
What does in situ mean?
Looking at the overall system/procedure.
116
Temperature effects on reactions?
Higher temperatures speed reactions, lower temperatures slow them down.
117
Three different types of solutes?
Solids, liquids, gases.
118
Solubility limits?
All solutes have a limit to how much solute they can hold - saturation point.
119
Supersaturation?
Very unstable, precipitation and crystallization happens rapidly at nucleation site.
120
What are factors affecting colloid stability?
Size of particles, density of particles.

Culinary Chemistry (4 decks)

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