CHEMISTRY COMMUNITY

sarahwu3a

Both K+ and Na+ are derived from strong bases so they are extremely stable and will not form their strong bases in water, so they do not affect the pH.

sarahwu3a

You can do it both ways. If you multiply the H+ and OH- concentrations you should always get 1*10^-14, so they chose to solve for the OH- concentration that way but it is the same answer.

sarahwu3a

Normally you would write out the formula with the ligands in alphabetical order.

sarahwu3a

BF3 is an acid because the boron atom can still complete the octet by accepting another electron pair.

sarahwu3a

In the SO3 molecule, the sulfur atom has space to accept another electron pair so that in the molecule there are 4 regions of electron density in the molecule. Thus, as the electron pair acceptor it is the Lewis acid.

sarahwu3a

The first equation you wrote is correct. For the second part of the problem, look at both of the ions. Br- is the conjugate base of a strong acid so it is a weak base. NH4+ is the conjugate acid of a weak base so it is a strong acid. Thus the solution will be acidic.

sarahwu3a

They want you to write the equations as if the acid they give you is the acid. If you treat H2PO4 as the acid, HPO42- will be the conjugate base.

sarahwu3a

d is neutral as the salt is formed from a strong acid and strong base. e and f are both acidic because the copper and aluminum ions react with water to form Cu(OH)2 and Al(OH)3 leaving behind H+ ions that do not react with Cl- or NO3- ions as those stay completely dissociated. Thus, there are H+ ion...

sarahwu3a

Usually you would have to compare something like the strengths of the conjugate acid/base, but since we can't really do that now I doubt we'll see a salt like that.

sarahwu3a

Look at which species lose a hydrogen atom (the acid) and which species gain a hydrogen atom (the base).

sarahwu3a

Because HCl is a strong acid, you can assume 100% of the ions are ionized into H+ and Cl- ions. They give you the concentration of the solution which is also the concentration H+ ions which you can plug into the pH=-log(H+) equation. Then you solve for the pH of the solution with the same moles of H...

sarahwu3a

The conjugate base for B(OH)3 is B(OH)4. Is there a reason it wouldn't be B(OH)2H instead? Why does boric acid gain a hydroxide group instead of just donating a hydrogen proton?

sarahwu3a

The outline mentions we need to know the types of ligands, what are the types?

sarahwu3a

In the textbook, all the coordination compounds with water molecules are written as OH2 rather than H20, why is this? And do we have to write it the same way on the test?

sarahwu3a

Why is HF not a strong acid like HCl or HI?

sarahwu3a

AX2E is bent shaped.

sarahwu3a

Why is the I3- molecule linear? Shouldn't it follow the pattern that the lone pairs have more repulsion and make the molecule bent?

sarahwu3a

Another example of dipoles cancelling out is in CO2. The dipoles point in opposite directions and as they are the same magnitude, cancel out and CO2 is nonpolar.

sarahwu3a

for 2(b) if you draw out the Lewis Structure for the molecule, the carbon atom is single bonded to a hydrogen and an oxygen and double bonded to another oxygen atom. Thus, it has 3 regions of electron density and is sp2 hybridized, which is trigonal planar.

sarahwu3a

What direction should we draw the arrows for dipole moments? The textbook says to draw it towards the more electropositive one but I've seen it both ways.

sarahwu3a

Hydrogen only forms hydrogen bonds with N, O, and F because they are the only elements with high enough electro negativities to attract it.

sarahwu3a

Yes, usually more electrons makes stronger bonds but in this case AsF3 has a long pair compared to AsF5 with no lone pairs. This gives the molecule a strong negative dipole and as a result the molecule has both london and dipole-dipole IMF.

sarahwu3a

How would you go about comparing a very small molecule with hydrogen bonds vs a very large molecule with only london forces? Are hydrogen bonds always stronger?

sarahwu3a

For molecules with only 2 atoms and a single charge, how do you determine which atom gets the charge and which atom has a formal charge of zero?

sarahwu3a

Is it possible to have a bond that is both longer and stronger in comparison to another bond? Or should we assume that if a bond is longer, it is weaker than the bond in comparison?

sarahwu3a

If the compound is negatively charged the electrons should indicate so, the only thing you have to add are a minus sign and brackets around the molecule.

sarahwu3a

What is the trend for electron affinity? Does it just go horizontally or is it diagonally like the other trends?

sarahwu3a

Yes, the textbook says that if the difference between the two elements is about 2, the bond is ionic.

sarahwu3a

Sn will have 8 valence electrons.

sarahwu3a

How do you calculate bond order between a pair of atoms?

sarahwu3a

Nonmetals are usually more electronegative than metals as they're located further to the right on the period table and they tend to want to gain electrons rather than lose them.

sarahwu3a

Are we going to have to memorize molecular geometry for the midterm?

sarahwu3a

Oxygen is more electronegative as Chlorine is down a period so it has less pull on the outer shell of electrons.

sarahwu3a

Yes both electronegativity and ionization energy increase as you go up the periodic table and down the period.

sarahwu3a

Why is that IE decreases diagonally down the periodic table and not straight down?

sarahwu3a

The questions says when n=7, so l has the possible values of 0,1,2,3,4,5,6 which is 7 options.

sarahwu3a

I believe the question is asking you to classify each of the options as ground or excited states, there shouldn't be one correct answer.

sarahwu3a

The mass of a proton/neutron is a 1.67 × 10-27 kg

sarahwu3a

For a particle in a box, the textbook mentions that the particle has zero potential energy inside the box and infinite potential energy outside of the box. Why is this?

sarahwu3a

You can ignore the 60 W description. Use the wavelength of the light to calculate the the frequency, and then the energy of a photon of that wavelength of light. If there are 11 J total, divide 11J by the solved energy to get how many photons there are.

sarahwu3a

If a question asks about speed of light not in a vacuum you should be able to calculate that speed using the index of that material.

sarahwu3a

I don't think you need to memorize all the wavelengths for light but knowing that visible is about 400-700nm is definitely going to be necessary!

sarahwu3a

Plancks constant is essentially only used in Einstein's equation E=hv to find the energy of a photon with a given frequency.

sarahwu3a

You only need to use the equation for kinetic energy KE=1/2mv^2. I don't think the work function has anything to do with the answer.

sarahwu3a

I remember in lecture Professor Lavelle mentioning how according to the photoelectric effect electrons can be emitted without having any KE (energy of photon is the same as the work function) but in an experiment, how would one detect that the electron was emitted?

sarahwu3a

Is there any time during a lab that a value does not have sig figs that contribute to a calculation?

sarahwu3a

As long as it's legible I think it doesn't matter if it's pen or pencil!

sarahwu3a

When calculating for limiting reactants, does it matter which product you use as a final determination of the limiting reactant? Ex: combustion reactions can you find limiting reactants based on how much CO2 or H2O they produce?

sarahwu3a

Are there 3 or 4 sig figs in 8340?

sarahwu3a

Hydrogen gas is in the form H2 so while the mole ratio of hydrogen gas to potassium is 1 to 1 the mole ratio of hydrogen atoms is 2 to 1.

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