CHEMISTRY COMMUNITY

Sabina House 2A

Just to add, by this he means that if you calculate the [H3O+] to be less than 10^-7, then the amount of H3O+ normally in water caused by the autoprotolysis reaction influences the pH more than the amount of H3O+ generated by an acid. If you calculate that the acid generates 10^-9 M of H3O+ ions, th...

Sabina House 2A

The pH for strong acids is just the negative log of the molar concentration because for strong acids, all of the acid dissociates into H3O+ ions and A- ions (A- refers to the conjugate base of an acid). If the strong acid completes dissociates into H3O+ and A-, then the initial concentration of the ...

Sabina House 2A

Ionization percentage is the amount of acid or base that has turned into its conjugate acid or base. The formula for ionization percentage for acids is [A-]/[HA] * 100% and for bases it's [HB+]/[B] * 100%. The value of HA and B are the initial concentrations of the acid and base before equilibrium h...

Sabina House 2A

Because the initial solution was supposed to be a concentration of 0.025 M, and it is a strong acid, the concentration of H+ would have been 0.025 M. You can find the desired pH by doing -log[0.025]. To find the actual pH, you can use the formula M1V1 = M2V2 to solve for M2. M1 would be 0.025M, V1 ...

Sabina House 2A

Because the initial solution was supposed to be a concentration of 0.025 M, and it is a strong acid, the concentration of H+ would have been 0.025 M. You can find the desired pH by doing -log[0.025]. To find the actual pH, you can use the formula M1V1 = M2V2 to solve for M2. M1 would be 0.025M, V1 w...

Sabina House 2A

I think you would be given the units of the pressure of a gas. If they ask for a different unit in the answer, then you could just convert between the units, but bar and atm are very similar in value so there is not much difference between their values.

Sabina House 2A

In this problem, anything that is aqueous on both sides of the equation would not be in the net ionic equation since it does not change. In this case, Na and NO3 would be removed to form the net ionic equation because they are aqueous on both sides of the equation. Then you just need to take what is...

Sabina House 2A

I believe that adding water to the reaction would not affect the equilibrium since water is a liquid so it would not be included in the equilibrium expression. Because water is in excess and the concentration does not change very much before or after the reaction, adding water to the reaction does n...

Sabina House 2A

You can tell this reaction would be endothermic because it involves breaking the bond between the two atoms of X. Anytime you are breaking bonds it requires energy so the reaction would be endothermic, taking in heat in order to power the reaction.

Sabina House 2A

For this problem, anything that is aqueous on both sides of the equation would not be in the net ionic equation since it does not change. So in this case Na and NO3 would be removed to form the net ionic equation. This would leave you with 2Ag+(aq) + 2OH-(aq) <--> Ag2O(s) + H2O(l).

Sabina House 2A

For this problem, you can start by making an ICE table with H2, I2, and HI. You start with 0.300 M of both H2 and I2 based on the moles and liters they give you in the problem. You start with 0 M of HI. You can put these values into the initial concentration row. For the change in concentration, H2 ...

Sabina House 2A

Before you plug the values into the equation, you must convert them into moles/L. They start by giving you the values in mmol and give you the volume of 0.500 L so you must convert the mmol to mol and then divide that value by 0.500 L for each. That should give you the correct answer.

Sabina House 2A

Based on the problem and what you said you did, you should get the correct answer. The equation to use would be PV = nRT or P = nRT/V which is the same thing as P = conc(RT). If you plug in the concentration, correct R value, and temperature in Kelvin, you should get the correct answer. I would doub...

Sabina House 2A

Just to give another way to think about it, heating a reaction would favor the reaction in the endothermic direction. Since the forward reaction is exothermic, the endothermic reaction would be the reverse reaction so this would be favored. Therefore, the equilibrium would shift left. Hope this helps!

Sabina House 2A

Something with more resonance would be a stronger acid because the electrons would be delocalized. Electron delocalization stabilizes molecules and therefore leads to a more stable conjugate base of an acid. If a molecule has more double bonds, there is resonance to delocalize electrons, so this mol...

Sabina House 2A

I think the main way to tell is just that amphoteric oxides follow a diagonal line along the metalloids. The oxides with elements on the left side of the periodic table are basic and those with elements on the right side of the periodic table are acidic, so those in between are amphoteric. These amp...

Sabina House 2A

Just to add on, when going left to right across a period, the number of shielding electrons does not increase but the number of protons does increase. This means that the valence electrons are being pulled in by a greater force (from more protons) but there are not more shielding electrons to counte...

Sabina House 2A

In general you should use formal charges to determine Lewis structures to ensure you have the correct structure. However, when determining molecular shape, it does not matter if a bond is a single or double bond because it is counted as one region of electron density. So if you have a structure with...

Sabina House 2A

To find when the bond angle is slightly less than a value, you look at the number of areas of high electron density. This would include bond areas and lone pairs. In O3, there are two bond regions and one lone pair region, meaning there are 3 regions of electron density. Three regions of electron de...

Sabina House 2A

Chelating ligands are ligands that attach to a metal atom in two or more areas. This would make them polydentates.

Sabina House 2A

An electron withdrawing atom would be an atom that has the power to pull some electrons away from the atom it is bonded to in order to stabilize the negative charge on that atom by delocalizing electrons. An example he gave is Cl bonded to O versus Br bonded to O in ClOH and BrOH. Cl has a higher el...

Sabina House 2A

I think we are just supposed to know that if the coordination number is 4, it could be square planar or tetrahedral, but we don't have to know how to tell which one it is.

Sabina House 2A

[Pt(en)Cl2] would have a coordination number of 4. This is because there are in total 4 different bonds to the central atom, Pt. There are two Cl which each contribute one bond to the central atom. The (en) stands for ethylenediamine which is a bidentate, meaning it forms two bonds to the central at...

Sabina House 2A

The coordination number is the number of bonds to the transition metal atom in the coordination complex. The elements in the bracket are the only elements directly bonded to the transition metal atom. Fe would be the central transition metal atom and the 4 Br atoms would be bonded to it, so therefor...

Sabina House 2A

For the trigonal bipyramidal arrangement, if the lone pair was in the axial position, it would be 90 degrees from three different bonds (the bonds at the equatorial positions). However, if the lone pair was in the equatorial position, it would only be 90 degrees from 2 bonds (the bonds in the axial ...

Sabina House 2A

If there are two of the same atom on each side of a central atom (with no lone pairs on the central atom), the overall molecule would be nonpolar. However, the individual bonds inside the molecule are still polar bonds because they are between different atoms, but because the molecule is linear, it ...

Sabina House 2A

Something has a delocalized pi bond when it has resonance structures that each have a different location for one pi bond. In other words, if a pi bond can be drawn in different places, then that pi bond would be delocalized. For this question, out of the three in the first part of the question that ...

Sabina House 2A

The negative pole on a molecule would be on the atom in a bond with a higher electronegativity. If the atoms in a bond are not the same, there will be a negative and positive pole, even if it is very small. If oxygen is bonded to hydrogen, oxygen would have the negative pole because it has a higher ...

Sabina House 2A

To find the valence electrons in the d-block, you should include the s-block electrons from the period of that element as well as any d-block electrons in that period. You can do this by counting over from the left side of the periodic table towards the element. For example, Mn would have 7 valence ...

Sabina House 2A

Often times, the electron arrangement differs from the shape when there are lone pairs in a molecule. The electron arrangement of a molecule is where there are regions of electron density, whether that be bonds or lone pairs. However, when finding the shape of a molecule, you only pay attention to t...

Sabina House 2A

Another thing to note is that if a resonance structure is very unfavorable, it will contribute very little to the overall resonance hybrid, but it still contributes a very small amount because it is a possible resonance structure. The most favorable and lowest energy resonance structures contribute ...

Sabina House 2A

Mn would normally have 5 electrons in the 3d subshell and 2 electrons in the 4s subshell. If it were to lose 3 electrons, it would lose them from the 4s subshell first because it is higher in energy when it is filled and then it would lose 2 additional electrons from the 3d subshell to lose a total ...

Sabina House 2A

Often Lewis structures are used to show covalent bonds, but there are also Lewis structures to represent ionic bonds. An example would be for NaCl, where you would draw a Na+ ion with a bracket showing its + charge and a Cl- ion next to it with 8 lone pairs representing its full valence shell, as we...

Sabina House 2A

Just to add, elements want to have the same amount of electrons belonging to them as they have valence electrons, so the more atoms that can fulfill this requirement the better the structure. Some atoms are more likely to accept a negative formal charge due to their electronegativity, and some atoms...

Sabina House 2A

There are dipoles between any two atoms that aren't the same, they are just very small for some atoms. Between C and H, there is a dipole but it is very small because their electronegativities are very similar. If the same atom is bonded to itself, there is no dipole. Also one thing to note is that ...

Sabina House 2A

The 4s orbital is not higher in energy until it has been filled. So for K, Ca, and any element after Ca, the 4s is lower in energy while it is empty. This would cause electrons to fill that subshell before the 3d subshell. Once the 4s subshell is filled, it would become higher in energy than 3d agai...

Sabina House 2A

Yes, I believe that for 1 mole of Na+ and 1 mole of Cl- interacting, the total energy of their interactions is -250 kJ.

Sabina House 2A

The reason Ga would form an ion of 3+ is because it has 3 electrons in its outer shell, 1 in the 4p subshell and 2 in the 4s subshell. If Ga were to become an ion, it would lose all of the electrons in its outermost shell, which would be 3 electrons. It would not lose the electrons in the 3d subshel...

Sabina House 2A

For that question, I believe the way to solve it is to find the atom with the formal charge as close as possible to the oxidation number. So if the oxidation number of an atom is 7+, you would choose the resonance structure with the atom that has a formal charge closest to 7+. Hope this helps!

Sabina House 2A

For some molecules, not all the formal charges can be zero. This is because if you add up all the formal charges of atoms in a molecule, you get the overall charge of that molecule. So for a molecule with a 2+ charge, the formal charges of the atoms have to add up to that value so some of the atoms ...

Sabina House 2A

If you are referring to the sapling homework, they are talking about bond character in terms of the length of the bond between two atoms. If the bond is a double bond, that bond would be shorter than a single bond between the two same atoms. When sapling asks if a bond is ample in one property, it i...

Sabina House 2A

For Ni(2+), the Nickel neutral atom has lost 2 electrons. The electron configuration for a neutral Nickel atom would be [Ar]3d84s2. When Nickel loses 2 electrons to become Ni(2+), the electrons are lost from the 4s subshell because when it is filled it is higher in energy than the 3d subshell. Becau...

Sabina House 2A

To determine the valence electrons for each element, you can look at the group number of that element. For group 1 and 2, they each have 1 and 2 valence electrons respectively, meaning they have the same amount of valence electrons as their group number. For groups 13-18, you have to subtract 10 fro...

Sabina House 2A

To expand, orbitals are part of subshells, and can hold either the same or less electrons. One example of a subshell would be 2s, which can only hold 2 electrons because it contains one orbital (and each orbital holds 2 electrons). However, the subshell 2p has three orbitals in it so it can hold 6 e...

Sabina House 2A

For elements with the same number of electrons, the atom with more protons in the nucleus or the higher effective nuclear charge has the smaller atomic radius. In the case of Na+ and F-, Na+ has the smaller ionic radius because it has a stronger pull from the nucleus, causing electrons to be pulled ...

Sabina House 2A

If you look at the periodic table, you can see that oxygen has 4 electrons in the p-block. The p-block only has 3 orbitals, so two of those electrons are paired up in one orbital with opposite spins. If you were to take one of those electrons away, there would be 3 p-block electrons and they could e...

Sabina House 2A

I think he said in the lecture that in theory l could be equal to 4, but we don't have elements that are this high. So in the periodic table, there are no elements with l=4.

Sabina House 2A

Yes, the wave must connect at both ends by having a full wavelength. It must also have a constant wavelength and amplitude throughout the whole wave so it does not vary.

Sabina House 2A

I believe the energy of Ep is usually given in J/photon, but pay attention to the question to make sure your units match for each of the values in that equation. If you have the energy in J/photon, you can multiply by Avogadro's number to get J/mol of photon.

Sabina House 2A

SI units are always in kg, not g. Because of this, the constant h used in the Heisenberg's indeterminacy equation is in units of J/s, and 1 J = 1 kg m^2 s^-2. Because the constant h uses kg, you must use units of kg for the mass.

Sabina House 2A

Yes, that would be the correct way to solve the problem. I got a slightly different answer for the yield of NO from 15.6g NH3 (I got 27.49g NO produced) but either way O2 is still the limiting reactant and your answer would be correct.

Sabina House 2A

For this problem, you can figure out the event based on the wavelength of the electromagnetic radiation. For your example, the wavelength is 340 nm, which is in the ultraviolet portion of the electromagnetic spectrum, so this event is acquiring a suntan. By comparing each wavelength calculated to th...

Sabina House 2A

Yes, you are correct. While all matter has wavelike properties, it can only be detected at a small mass due to De Broglie's equation, wavelength = h/p. Also, electrons do have both wave and particle like properties.

Sabina House 2A

I believe that rounding those answers to 8.0 and 5.0 is correct if using two sig figs.

Sabina House 2A

Yes, you are correct. Because E(photon) - work function = Ek, you could rearrange this so work function = E(photon) - Ek. This means that the energy required to remove an electron is the (energy of a photon) - (kinetic energy of the ejected electron).

Sabina House 2A

What those statements mean is that for each of the series, it involves electrons starting at a certain electron energy level and being excited to a higher level, or starting at various high energy levels and jumping back down to one standard energy level. For the Lyman series, which is in the ultrav...

Sabina House 2A

Yes, more energy is required for an electron to jump from n=1 to n=5 than from n=2 to n=4. Because of this, a shorter wavelength of light must be emitted when going from n=5 to n=1 because shorter wavelengths contain more energy. The transition from n=4 to n=2 would emit longer wavelength light beca...

Sabina House 2A

You use the mass of an electron, 9.109 * 10^-31 kg, which can be found in the back of the book. You know to use this mass because you use the mass of the object you need to find the kinetic energy of. Since in this situation you are finding the kinetic energy of an electron, you use the mass of an e...

Sabina House 2A

My understanding is that light intensity is simply how bright a light is, and increasing the intensity increases the amount of photons being emitted by that light source. The wavelength and frequency are independent of the amplitude, and are instead dependent on the length of a wave. So changing the...

Sabina House 2A

For this problem, you start by turning the frequency into energy using E = hv. Then, you calculate the energy of the n=4 level by using the En = -hR/n^2 equation. Because Efinal - Einitial = difference in energy, you can plug in the energy difference you calculated using the frequency (which should ...

Sabina House 2A

If the molar ratio was equal to the calculated moles that would mean there is no limiting reactant because each reactant has the perfect amount of moles to react with each other. To find the amount of product formed you could use moles of either reactant because they both are able to produce the sam...

Sabina House 2A

For this problem, I start by converting the 0.500 grams of KCl, K2S, and K3PO4 all into moles by using their molar masses. Once I had the moles, I knew the moles of KCl = moles of K, 1 mole of K2S = 2 mole K, and 1 mole K3PO4 = 3 mole K. I used these conversion factors to convert from moles of each ...

Sabina House 2A

If a number has decimal places, it usually has the same amount of sig figs as digits in the number. For example, 4.00, 40.2, and 5.46 all have 3 sig figs because they all have 3 digits. However, in a number like 0.029, there are no digits present before the 2, so this value would only have 2 sig fig...

Sabina House 2A

Because a molecule of O2 has two oxygen atoms instead of just one, the total mass would be 32 g/mol rather than 16 g/mol which is for just one oxygen atom.

Sabina House 2A

In this problem, it is also mentioned that there are 17.5g of CO2 produced from the thermal decomposition, which has 3 sig figs. Because the last step involves the 17.5g, the answer should be 93.1% with 3 sig figs.

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