CHEMISTRY COMMUNITY

John Arambulo 1I

In a strong acid-strong base reaction, both the acid and base ionize completely, so the concentration of H3O+ and OH- would be equal assuming that the concentrations of the acid and base are equal. In a strong acid-weak base reaction, there would be H3O+ ions leftover after completion of the reactio...

John Arambulo 1I

Cl is definitely more electronegative than P which does account for why HClO4 is stronger, but you must look at the stability of the anion (conjugate base). ClO-4 has more resonance than H2PO4- (you can look up their structures on google), so it allows for more delocalization of the negative charge,...

John Arambulo 1I

Acids/bases are deprotonated/protonated one at a time. So there would be multiple reactions to show the loss of the protons in polyprotic acids. For example phosphoric acid, 3 protons to get to the phosphate ion. http://guweb2.gonzaga.edu/faculty/cronk/biochem/images/phosphate-triprotic-system.gif

John Arambulo 1I

Ka's are usually given to you, unless the problem is asking you to calculate the Ka from the given concentrations of the products and reacts, but that won't be dealt with until chem 14b.

John Arambulo 1I

If the resulting anion, known as the conjugate base, can have its negative charge delocalized, by resonance or inductive effect (electron-withdrawing ability of other electronegative atoms), it is more stable and thus a stronger acid.

John Arambulo 1I

How did you post the images there? I've tried to do the same to post replies but don't know how. When you find an image on google images or wherever, instead of clicking on "Copy," click on "Copy image address. Then you would paste the image address inside after clicking on "Img...

John Arambulo 1I

There are no rules in distinguishing strong or weak acids. There are trends/guidelines to help you know/predict if an acid is strong or weak relative to another one. You can look down a group, across a period, and or see if there is resonance and or inductive effect.

John Arambulo 1I

Generally, a strong base, like NaOH, ionizes completely in water. So metal oxides, formed from alkali and alkaline earth metal with oxygen, such as Na2O, would react with water to form a strong base such as NaOH. This is because the oxygen atom acts as a lewis base (donates electron pair) to deproto...

John Arambulo 1I

To understand why acids are stronger or weaker relative to each other, it is important to look at the stabilities of the conjugate bases. In general, the more stable a conjugate base is, the stronger its acid is. Often times, resonance is one of strongest contributors to stability because it can off...

John Arambulo 1I

NaOH, the entire compound, is considered a base (a STRONG base, even). A bronsted base is defined as anything that accepts a proton. But the textbook explicitly states that Na+ is the spectator ion and OH- alone is the Bronsted Base. It warns us to not confuse it with what you said about NaOH being...

John Arambulo 1I

A base in general is a species that can accept a proton to form hydroxide ions. A strong base is one that can readily accept this proton. This means that if you were to have a solution containing a strong base, like NaOH, this species will readily dissociate to form an excess of hydroxide ions. Orga...

John Arambulo 1I

NaOH, the entire compound, is considered a base (a STRONG base, even). A bronsted base is defined as anything that accepts a proton.

John Arambulo 1I

When Dr. Lavelle was discussing the heme complex for myoglobin for biological examples, it made me wonder what the structure of the heme complex would look like for a person with sickle cell trait or sickle cell anemia. I know that the mutation from sickle cell causes the red blood cells to clump up...

John Arambulo 1I

Another example is chlorophyll where Mg+2 binds to 4 nitrogen atoms.

John Arambulo 1I

Hybridization is based on the number of regions of electron density.

John Arambulo 1I

The oxygen binds to the Fe+2 ion in the heme complex.

John Arambulo 1I

Cis-platin and how it interacts with the guanine in DNA. I feel like he'd put this because he spent a good amount of time explaining it.

John Arambulo 1I

Heavier halogens have more electrons in their shell which increases Van Der Waal forces and boiling point Not just heavier halogens, larger molecules, in general, have stronger Van der Waal forces (induced dipole-induced dipole, London dispersion forces) because they have more surface area for dist...

John Arambulo 1I

It allows expanded octets to form when the central atom is in the third period and down the periodic table. It can accommodate more electrons, as atoms in the p-block of the third, fourth, and fifth period have empty d-orbitals, and the examples of this in VSEPR are trigonal bipyramidal and octahedr...

John Arambulo 1I

Bonding electrons are stabilized in the covalent bonds between the atoms with bond length, strength, order, and hybridization being taken into account. With lone pairs, charge density is more spread out (electron cloud around the atom), so their repulsion strength is stronger than bonded electrons.

John Arambulo 1I

Polarizability is a concept of size with anions and cations. Since anions are larger than their respective neutral states because of having more electrons, it is easier to distort (move the electrons around the atom) the electron cloud. With respect to cations, they have polarizing strength, meaning...

John Arambulo 1I

Also, atomic size affects bond angles because a larger atom would have more electrons, thus having more electrons, making the bond angles smaller.

John Arambulo 1I

Compounds with higher boiling points generally means that the bonds present in the compound are stronger, since it will require a higher temperature for the substance to change state. It requires a higher temperature because the bonds are stronger and therefore harder to break apart. This could sig...

John Arambulo 1I

A dipole-dipole force is between two dipoles like HCl and HCl. A dipole-induced dipole is between a dipole and a nonpolar molecule. The dipole distorts the electron cloud of the molecule, so the electrons shifts around the nucleus, causing a partial positive and partial negative charge, that becomes...

John Arambulo 1I

Because that is the only way to attain a neutral structure with an overall charge of 0.

John Arambulo 1I

You would know depending on whether it is a single, double, or triple bond. If the types of bonds are the same, then you would know if the bond lengths are shorter or longer based on the periods the atoms are on. Because atomic radii increase from top to bottom on the periodic table, the bond length...

John Arambulo 1I

Yes, but ionic bonds are almost always between the cation and anion whereas covalent bonds are shared between atoms. Ionic bonds can have covalent character while covalent bonds can have ionic character which is why Dr. Lavelle didn't specify if the bond is ionic or covalent when the difference in e...

John Arambulo 1I

An increase in size and molar mass means that there is more surface area for the atoms/molecules to have London dispersion forces. Although instantaneous and short-lived, the interaction is stronger with larger atoms and molecules because there are more electron distortion and polarizability of of e...

John Arambulo 1I

Hydrogen bonding is a special type of dipole-dipole interaction due to the high electronegativity of Nitrogen, Oxygen, and Fluorine, so hydrogen bonds occur in water, ammonia, and hydrogen fluoride. They can only occur when there are lone pairs around those atoms.

John Arambulo 1I

High distortion means that the electron cloud of the electron-rich anion can be easily distorted by a polarizing cation. The reason is that the high number of electrons can be easily moved/shifted around the nucleus as another charged ion or molecule gets close to the vicinity of it.

John Arambulo 1I

Chlorine can form double bonds if it is the central atom because it can utilize its 3d orbitals to have an expanded octet. Generally, when bonded to a central atom, halogens usually form single bonds.

John Arambulo 1I

The larger the difference between electronegativity is the extent to which a covalent bond has ionic properties because the bond gets more polar as the difference in electronegativity increases.

John Arambulo 1I

Anions are generally much larger than cations because they gain electrons to attain the octet, and we already know that anions are negative ions while cations are positive ions. When a cation gets closer to the vicinity of an anion, the positive charge distorts the electron cloud of the negatively c...

John Arambulo 1I

A hydrogen bond is a type of dipole-dipole attraction, but it is stronger because the hydrogen atom(s) are covalently bonded to oxygen, nitrogen, or fluorine. Because there are only one proton and one electron in the hydrogen atom, when it is bonded with oxygen, nitrogen, or fluorine, the dipole mom...

John Arambulo 1I

You would know based on the electronegativity of the elements by using the periodic trends and also by formal charges because a negative formal charge would mean the electron density his higher around that atom.

John Arambulo 1I

A molecule will always be covalent because it is covalently bonded. The dipole moment determines whether the covalent bond has ionic or covalent character because of the charge difference. If there is a dipole moment, it is a polar covalent bond, and as a result of the partial positive and partial n...

John Arambulo 1I

You would count the number of electrons in the lone pair and bonds individually. But here's a shortcut to calculate the formal charge…
Formal charge=(#of valence electrons for the atom)-(Total number of lone pair electrons and bonds on the atom)

John Arambulo 1I

Yes, a higher number of electrons results in an increase in shielding and a decrease in effective nuclear charge. This is because an increased number of electrons between an atom's positive nucleus and the atom's valence electrons results in both increased attraction between the internal electrons a...

John Arambulo 1I

Electron affinity is the absolute value of the energy associated with an atom in the gas phase gaining of an electron. All this means is that electron affinity describes the ease at which an atom in the gas phase accepts an electron.

John Arambulo 1I

You have to take into account all of the atoms in the Lewis structure and the overall charge of the molecule because it is more stable when the negative formal charge is on the more electronegative atom and the positive formal charge is on the less electronegative atom.

John Arambulo 1I

Any of the elements in the third principal energy level and higher because they can accommodate more electrons with their d- orbitals. Other common examples are Si and Xe.

John Arambulo 1I

The reduced electrostatic attraction due to the distance from the nucleus, electron-electron repulsions, and shielding from the inner energy levels and subshells results in an effective nuclear charge, and the result is an increase in the size of the atom.

John Arambulo 1I

As you go down a group, the radius increases because the principal quantum number (n) increases, but you have you take more into account. The nuclear charge increases because there are more protons pulling electrons, but the effective nuclear charge is affected because the electron-electron repulsio...

John Arambulo 1I

The angular momentum quantum number is used to describe the 'shape' of the orbital whether l= 0 (s), 1 (p), 2 (d), or 3 (f).

John Arambulo 1I

In addition to what Chem_Mod said about angular momentum quantum number and magnetic quantum number, the angular momentum quantum number describes the 'shape' of the orbital while the magnetic quantum number describes the orientation in space of the different orbitals of a subshell.

John Arambulo 1I

It will still be 3 and 5 respectively unless the magnetic quantum number, $m_{l}$ , is given.

John Arambulo 1I

You would need to know the energy of the object if you wanted to calculate its frequency using the De Broglie equation because E=hv. You would need to substitute E/v for h into the De Broglie equation to solve for frequency.

John Arambulo 1I

The photon (particle) and wave model are different because, in the photon model, the intensity is proportional to the number of photons present at each instant, while in the wave model, the intensity of electromagnetic radiation is proportional to the square of the amplitude of the wave. These show ...

John Arambulo 1I

Electrons can be excited from any principal energy level (n=1, 2, 3, etc). At the same time, when you use Rydberg's equation to calculate the energy change, the final energy level does not have to be where the electron was originally before it was excited. When an electron is excited, it goes back d...

John Arambulo 1I

This question is similar to the worked example under the photoelectric effect during the lecture. In part A, you calculated the threshold energy to remove an electron which is the work function, \phi , which is 7.22 x 10^-19 J. Since you are looking for the kinetic energy, E_{k} , you must first cal...

John Arambulo 1I

Where does Planck's constant come from? I know that it is used to relate the energy in a photon of electromagnetic radiation to the frequency, but how was it derived? In the field of quantum mechanics, Planck's constant is used literally everywhere, so I'm curious as to where the constant originated...

John Arambulo 1I

Planck's constant is used to relate the energy in one photon or packet of energy (quanta) of electromagnetic radiation to its frequency. His idea was that a charged particle oscillating at a frequency \nu (nu) can exchange energy with its surroundings by generating or absorbing electromagnetic radia...

John Arambulo 1I

I wouldn't say that this is an official or first choice way of determining the limiting reactant because there are multiple variables that have an influence on this way of conceptualizing the limiting reactant, but from the limiting reagents module, I realized there is a correlation with the stoichi...

John Arambulo 1I

I’m not exactly sure what kind of chemical reaction it was when your TA was balancing an equation for one of your discussion problems, but in general, oxidation numbers are essential for oxidation-reduction (redox) reactions. The reason for this is because, in redox reactions, electrons are stripped...

John Arambulo 1I

When doing molarity and dilution problems, it is essential to know which of the given volumes and concentrations correspond with each other. For example, 50mL of a 0.5M sol of A, and you want to calculate the concentration of 250mL of sol B that would neutralize sol A. To solve this, I make sure I k...

John Arambulo 1I

Would it also be necessary to write out the formula being used in answering a question? I don't think it is necessary to show the formula being used when answering a question because the TA would know which formula you're using when you have the values plugged in already, but it is helpful to have ...

John Arambulo 1I

In the problems we've done, I would say showing work for conversions such as mL to L wouldn't need to be shown, but for everything else such as molar mass, molarity, and other aspects of dimensional analysis should be shown.

John Arambulo 1I

If the problem doesn't directly tell you the states of the reactants or products, you can determine it based on the reaction knowing if the reaction occurs in an aqueous solution. Most products from reactions in aqueous solutions are also aqueous. If you know that one of the products is a precipitat...

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