CHEMISTRY COMMUNITY

Rose_Malki_3G

When the k value is less than 10^-4 we can assume the x value is insignificant. Also if the percent ionization is less than 5%, we know the x value is insignificant.

Rose_Malki_3G

I believed that knowing the actual temperature isn't necessarily important for the calculations we have been doing but it is important to know if temperature has changed or not because if temperature changes, then the kb/ka value will change as well.

Rose_Malki_3G

This is because if the ph is lower than the pKa value it means that the surrounding solution is more acidic than the actual species, therefore it the species will not deprotonate and will remain neutral

Rose_Malki_3G

In the case of acids, a low pKa or a high Ka is an indicator of a strong acid. Whereas for a base, a low pKb and/or a high Kb is an indicator of a strong base

Rose_Malki_3G

It depends on which way the reaction is moving. If it is going in the forward direction, then it would be -x for the reactants and +x for the products. If the reaction is moving in the reverse direction, then it would be -x for the products and +x for the reactants.

Rose_Malki_3G

Phase change means that a substance has changed from one state of matter to another. An example of this would be liquid water becoming water vapor.

Rose_Malki_3G

Are the units of ΔH⊖rxn always just Kj whereas the units of ΔH⊖f always Kj/mol?

Rose_Malki_3G

Yes we use them in the ice chart like we would with concentrations. You do not need to convert the units.

Rose_Malki_3G

We do not include liquids nor solids in the equilibrium expression so the amount to solid or liquid won't cause a change in the equilibrium

Rose_Malki_3G

If the equation is shifting to the left, it means it will produce more reactants. If the equation is shifting to the right, it means it will produce more products

Rose_Malki_3G

Because the overall pH of the solution (9.57) is greater than the pKa, the neutral, deprotonated species of B will become more predominant in solution.

Rose_Malki_3G

Yes you can use Ice table for both partial pressures and concentrations.

Rose_Malki_3G

Yes Q will eventually reach K. And Q is expressed when equilibrium has not yet been reached.

Rose_Malki_3G

Inert gases are just noble gases

Rose_Malki_3G

You do not include solids nor solvents because their concentrations do not change by any significant amount.

Rose_Malki_3G

Yes if the reverse reaction were being executed then you would have an initial concentration for the products.

Rose_Malki_3G

Because 1 bar is approximately equal to 1 atm we use both and don't necessarily prefer one over the other. However, I do believe the SI unit is bar

Rose_Malki_3G

If you have an endothermic reaction, then you can think of heat as a reactant so if you were to release heat, the reaction would shift to the left whereas if you increase heat, it would favor the products/forward reaction.

Rose_Malki_3G

You typically use ice chart when you know the reactants aren't being used up to completion. Usually you are given the initial conditions and you are trying to find the change in concentrations in order to determine the final equilibrium concentrations.

Rose_Malki_3G

Because this bond is ionic, you do not use prefixes in naming it

Rose_Malki_3G

Polydentate ligands will form chelate/ring attached to the transition metal.

Rose_Malki_3G

If there are 4 regions of electron density with 3 of them being bonded pairs and one being lone pair, then the lone pair will create more repulsion, causing the bonded pairs to be pushed down, making their bonds closer together (so less than 109.5)

Rose_Malki_3G

HCl is a stronger acid because a strong acid is one that easily loses a proton/hydrogen. Cl has less electronegativity than F so the bond between H and Cl is weaker than that between H and F, making HCl the stronger acid. And for c, HClO2 is stronger because Cl has higher electronegativity than Br s...

Rose_Malki_3G

First compare bond length. If bonds are the same in the compounds you are comparing then compare stability of the anions (so compare electronegativity)

Rose_Malki_3G

It would be sp3 because there are 4 regions of electron density around the N (3 bonds with hydrogens and one lone pair)

Rose_Malki_3G

List the ligands in alphabetical order and add the suffix -ate when the complex has a negative charge

Rose_Malki_3G

use this list https://sites.google.com/site/chempendix/ligands to determine what type the ligand is.

Rose_Malki_3G

Check to see if the dipoles cancel it. If they do, then the species is non polar and if they do not cancel out, the species is polar.

Rose_Malki_3G

For this class, you do not need to distinguish between tetrahedral and square planar. Just know that they are the common shape for coordination number 4.

Rose_Malki_3G

Coordination number refers to the number of donor atoms from the ligands that are bonded to the central atom. To find this, determine what the ligands' types (mono dentate, bidentate, etc.) and based on this, count the number of atoms that are bonded to the centra atom. In [FeBr4]2 the coordination ...

Rose_Malki_3G

In the compound [Cd(en)Br2], what does the en stand for?

Rose_Malki_3G

What is the difference between a coordination compound and a complex ion? Is a complex ion just a coordination compound with a nonzero net charge.

Rose_Malki_3G

This is because the structures have different atom connectivities.

Rose_Malki_3G

Yes because, without a decimal present, ending zeros are not counted as significant digits

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Sigma bonds are single bonds whereas pi bonds occur in any bonds other than single bonds. Sigma bonds are more flexible whereas pi bonds are more fixed in their positions.

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Sigma bonds are more flexible and are single bonds whereas pie bonds are more fixed in their position and occur in double and triple bonds.

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This is because different resonance structures may have atoms with higher or lower formal charges. The resonance structure that is most stable is the one with atoms with the lowest magnitude of formal charge.

Rose_Malki_3G

Delocalized pie bonds occur when pie orbitals extend across more than 2 atoms in a molecule. In terms of lewis structures, you can show this by drawing multiple resonance structures.

Rose_Malki_3G

Atoms that are in the 3rd row or lower can have more than 8 electrons because they can fill their d states with electrons.

Rose_Malki_3G

It means that the atoms are not being moved but rather it is the actual electrons that are delocalized/move to create different resonance structures.

Rose_Malki_3G

Yes! And once you have found the total number of electrons, try to make each atom achieve an octet. If the central atom is in the 3rd group or lower, however, it can get an extended octet and have more than 8 electrons around it

Rose_Malki_3G

This is because the species is more stable if all of the orbitals in the d state are filled with 2 electron so an electron from the 5s state will move to the 4d state

Rose_Malki_3G

Electronegativity is essentially an atom's pull on electrons. The trend is that electronegativity increases as you go across a period and decreases as you go down a group

Rose_Malki_3G

If the dipoles of the polar bonds cancel each other out, then the overall species would still be considered non polar.

Rose_Malki_3G

Yes regions of electron density are bonding regions/electrons and lone pairs

Rose_Malki_3G

This is because the dipoles cancel each other out, making the molecular non polar

Rose_Malki_3G

If two species are isoelectronic, it means they have the same number of electrons. However, the two species will still have different properties as their nuclear charges are different.

Rose_Malki_3G

In general, it is usually assumed that the O2 is in excess so it would usually not be the limiting reactant.

Rose_Malki_3G

In #20 of the sapling assignment it asks you to choose which intermolecular forces of attraction are present between CH3CHO molecule. I was wondering why hydrogen bonding cannot be present here by connecting the oxygen atom to one of the hydrogen atoms?

Rose_Malki_3G

How do we use oxidation numbers to identify the most plausible lewis structure?

Rose_Malki_3G

In the #4 of the sapling assignment, it gives us a table of expected bond lengths and also informs us of the observed bond lengths. It then asks us to chose the correct statement about the lewis structure and bond lengths. In the answer options it says "the carbon–nitrogen bond has ample C=N bo...

Rose_Malki_3G

The difference in electronegativity between a carbon atom and a hydrogen atom is not great enough to make an interaction as strong as a hydrogen bond

Rose_Malki_3G

No a hydrogen bonding with another hydrogen is not considered hydrogen bonding. This type of interaction is also not favorable since hydrogen would be delta positive so two delta positive atoms would not be attracted to one another.

Rose_Malki_3G

I believe Nitrogen, being that it is only in the 2nd row, does follow the octet rule

Rose_Malki_3G

Since we have never been formally taught chemical formulas in this class, I don't think we are expected to know them during the test

Rose_Malki_3G

In Wednesday's lecture, Dr. Lavelle said that London interactions are always present and attractive. What did he mean by present? Like are London dispersion forces also present in compounds with ionic or hydrogen bonds?

Rose_Malki_3G

It represents lone pairs (electrons not involved in the actual bonding/not shared elections)

Rose_Malki_3G

Increases as you go across the table and decreases as you go down

Rose_Malki_3G

Because they are further from the nucleus and the further away an electron is, the more energized it is

Rose_Malki_3G

The one with a greater nuclear charge (in this case Na+) will be smaller because it has a greater hold pull on the electrons

Rose_Malki_3G

I do not think we will have to memorize these values (just remember that single bond is longer than double bond)

Rose_Malki_3G

Hydrogen is in the 1s state and therefore will not follow the octet guideline

Rose_Malki_3G

You use brackets whenever you want to specify the charge of a certain species (which can be both an anion or a cation)

Rose_Malki_3G

In the equation Ep - (threshold energy) = (kinetic energy)
what are the units of each energy? Is Ep in units of J/photon or J/mol of photon? And if it is in units of J/photon, would you just multiply by Avogadro's number to get it in J/mol of photon?

Rose_Malki_3G

If the work function is given to us in kJ/mol, do we need to convert it to J/photon (so we would need to multiple the work function by 1000 to go from kJ to J and then divide by Avogadro's number to change from per mol to per photon)?

Rose_Malki_3G

A .50-g sample of metallic tin was placed in a 26.45-g crucible and heated until all the tin had reacted with the oxygen in air to form an oxide. The crucible and product together were found to weigh 28.35 g. (a) What is the empirical formula of the oxide? (b) Write the name of the oxide When I was ...

Rose_Malki_3G

How would you go about balancing the following equation:
C10H15N + O2 -> CO2 + H2O + CH4N2O

Because the answer had very high coefficients so I was confused as to how to find the balanced equation using a method other than just guess and check

Rose_Malki_3G

An excited hydrogen atom emits light with a frequency of 1.14x10^14 Hz to reach the energy level n = 4. In what principle quantum level did the electron begin? Can someone please walk me through how to do this problem? Because whenever I get an answer using the rubber equation for n it is never a wh...

Rose_Malki_3G

I would recommend going through the textbook problems that he mentioned in the syllabus for extra practice. Also, I found the modules to be a great review of what Dr. Lavelle went over in the lectures

Rose_Malki_3G

You should only round your numbers to the correct number of sig figs once you have found your final answer

Rose_Malki_3G

If light is in the visible region (Balmer series), then the transition involves the n = 2 stage. Where as all traditions involving n =1 are with the ultra violet region (Lyman series)

Rose_Malki_3G

m sub l does not only equal l - 1. It can equal a range of values; m sub l equals 1, l-1,... -1. For example. if l equals 2, then m sub l can be equal to 2, 1, 0, -1, -2.

Rose_Malki_3G

The speed can be between 0m/s and 10m/s therefore the uncertainty in the speed is 10m/s (not 5)

Rose_Malki_3G

The speed can be between 0m/s and 10m/s therefore the uncertainty in the speed is 10m/s (not 5)

Rose_Malki_3G

In today's lecture, Dr. Lavelle talks about the silver atom used in the Stern and Garlach Experiment. He says that the silver atom has one unpaired electron in the 5s state. Can someone please explain to me why that is the case (because I would have thought the unpaired electron was in the 4d state).

Rose_Malki_3G

In photoelectric experiments, typically what part of the electromagnetic spectrum is the incoming light?

Rose_Malki_3G

Is the threshold energy the same thing as the work function?

Rose_Malki_3G

I know that the Lyman series corresponds to the UV region and the Balmer series is associated with the visible region, but is there a series name that corresponds to the infrared region?

Rose_Malki_3G

For the Rydberg equation that is equal to frequency, is there a negative sign in front of the Rydberg constant?

Rose_Malki_3G

You use the change in n values to find the frequency of the light emitted (using the V = -R((1/n^2)-(1/n^2)) equation). And then once you get the frequency, you use the equation c = (frequency)(wavelength) to solve for the wavelength

Rose_Malki_3G

For the equation V = -R((1/n^2)-(1/n^2))
How do we know which n value (the final or initial n value) to put first in the equation?

Rose_Malki_3G

Sorry meant to say sapling (not sampling)

Rose_Malki_3G

I know we are required to turn in the sampling problems through the website but are we required to turn in the textbook problems as well? And, if so, how/where would we turn them in?

Rose_Malki_3G

In 1.0 s, a 60 W bulb emits 11 J of energy in the form of infrared radiation (heat) of wavelength 1850nm. How many photons of infrared radiation does the lamp generate in 1.0s?

How would you go about finding the answer to this question?

Rose_Malki_3G

Are we expected to memorize the wavelengths associated with each region of any atom's electromagnetic spectrum? And, if so, which atoms would we need to do this for?

Rose_Malki_3G

The meter was defined in 1963 as 1,650,763.73 wavelengths of radiation emitted by krypton-86 (it has since been redefined). What is the wavelength of this krypton-86 radiation?

How would you solve this problem?

Rose_Malki_3G

If 1 million photons in the UV region are absorbed by a hydrogen gas sample how many electrons are excited to a higher energy level?

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