## Search found 43 matches

Sun Jan 10, 2021 11:40 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook question 5I.13
Replies: 2
Views: 29

### Re: Textbook question 5I.13

I have not done this problem yet, but I believe you just use the Kc values in the table they tell you about. At 1000K, the Kc of the disassociation of Cl is 1.2x10^-7 and the Kc for the disassociation of F is 1.2x10^-4. Then use the expressions Kc=[Cl]^2/[Cl2] and Kc=[F]^2/[F] to algebraically solve...
Sun Jan 10, 2021 11:18 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling #7
Replies: 3
Views: 18

### Re: Sapling #7

Since heat (which is energy) is being added, the reaction should shift to the right. The energy increase is on the product side so, adding more product will result in a shift to the reactant side of the equation. In exothermic reactions, adding heat will shift the equilibrium to the right (Q>K). In ...
Sun Jan 10, 2021 11:15 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: States that affect K
Replies: 5
Views: 18

### Re: States that affect K

I think what Hazelle said was right. Unlike aqueous solutions and gases, solids and liquids don't fully mix with each other. They are pure substances, therefore the concentration wouldn't change over the course of a reaction and they would not impact K.
Sun Jan 10, 2021 11:09 pm
Forum: Ideal Gases
Topic: Pressure and partial pressure
Replies: 12
Views: 38

### Re: Pressure and partial pressure

The equation relating these two things are P=P1+P2+...+Pn where P is the total pressure, P1 is the partial pressure of gas 1 and P2 is the partial pressure of gas 2, and so on and so forth until the number of gases in the mixture (n) has been reached. So pressure is the sum of all the partial pressu...
Sun Jan 10, 2021 11:01 pm
Forum: Ideal Gases
Topic: General Question
Replies: 5
Views: 21

### Re: General Question

An ideal gas is not technically a gas. In order for there to be an ideal gas, there would have to be no interparticle interactions between molecules of the gas. This is not really possible, but we simply assume that gases involved in these problems are ideal (aka the effect of the interparticle inte...
Thu Dec 17, 2020 3:47 am
Forum: Bronsted Acids & Bases
Topic: Textbook Problem J.9 part b
Replies: 3
Views: 28

### Re: Textbook Problem J.9 part b

The answer to your question, Megan, is what Zach meant when he said there would be some H3PO4 left at equilibrium. For Acid-Base reactions involving weak acids or weak bases, it is better to imagine the arrow as a double-sided arrow. Some of the H3PO4 molecules will ionize into H+ and PO43-, but som...
Thu Dec 17, 2020 3:41 am
Forum: Bronsted Acids & Bases
Topic: Textbook Problem J.9
Replies: 2
Views: 25

### Re: Textbook Problem J.9

The key to these problems is isolating out the OH- and H+ to form water and then pairing whatever is left together. For the rest of the problems, it would go as follows:

c) Ca(OH)2 +2HBr ----> 2H2O + CaBr2

d) 2NaOH + H2S ----> 2H2O + Na2S
Thu Dec 17, 2020 3:32 am
Forum: Bronsted Acids & Bases
Topic: Textbook Problem J.1 Part C
Replies: 3
Views: 27

### Re: Textbook Problem J.1 Part C

An easy way to avoid making this mistake in the future is focusing on the components of the molecule. If there is an O and an H right next to each other (usually at the end of a molecule) it is almost certainly a base. Also, molecules with N are often bases. In a similar fashion, molecules with an i...
Thu Dec 17, 2020 3:21 am
Forum: Amphoteric Compounds
Topic: Amphoteric Compounds trend
Replies: 2
Views: 24

### Re: Amphoteric Compounds trend

It's a little tricky since you pretty much just have to memorize those. It helps to think of them as almost being the diagonal line that marks where the metalloids are. It also helps me to trace it myself on the periodic table to get more of a feel for which ones they are and hopefully remember it l...
Thu Dec 17, 2020 3:17 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Acids in Water
Replies: 3
Views: 38

### Re: Acids in Water

I believe that the H+ reacts with H2O rather than the Cl- because Cl- is more electronegative and negatively charged. When an acid such as HCL mixes with water, the H+ is bonding with one of the lone pairs on the oxygen in the water molecule to form H3O+. Cl- is more electronegative and is, therefor...
Thu Dec 17, 2020 3:14 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Textbook Problem J.17
Replies: 3
Views: 66

### Re: Textbook Problem J.17

I'm not exactly sure what the correlation between weak acids and their conjugate bases is, but in this problem, C6H5O- is a weak base. The question is pretty much just asking whether the salt is going to make the pH of the water more acidic or more basic. Since C6H5O- attracts H+ and leaves OH-, it ...
Thu Dec 17, 2020 3:08 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Textbook Question 6C.17: Justification for Base Strength
Replies: 2
Views: 20

### Re: Textbook Question 6C.17: Justification for Base Strength

If you don't have access to the pKb values, you can use logic to sort of figure out which one is the stronger base. Just as the stronger acids will lose H+ more easily and have more stable anions, stronger bases will gain H+ more easily and have less stable anions. Since BrO- is already negative, it...
Thu Dec 17, 2020 3:01 am
Forum: Biological Examples
Topic: Cr - insulin Example
Replies: 2
Views: 53

### Re: Cr - insulin Example

Expanding a bit on Chromium and its role as a cofactor, Chromium is needed in order to activate certain enzymes in the body associated with insulin. The role of a cofactor is to bind to the enzyme and change the shape enough to allow the enzyme to function. Enzymes are proteins and the big thing abo...
Thu Dec 17, 2020 2:53 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Textbook problem 9C.9
Replies: 4
Views: 29

### Re: Textbook problem 9C.9

Similar to what Joey said, you just have to count the number of points that the ligands are attached to the central atom. [Ag(NH3)2]+ is one silver molecule attached to two ammonia molecules. Since ammonia is a monodentate ligand, the coordination number is 2. [Cr(edta)]- is a bit of a more special ...
Thu Dec 17, 2020 2:46 am
Forum: Naming
Topic: How to determine the charge of ligands?
Replies: 4
Views: 42

### Re: How to determine the charge of ligands?

It is useful to use the periodic table. All the halogens in group 17 (F, Cl, Br, I) have a charge of -1. Think of it as being one removed from the noble gases. They gain one electron to get a complete shell, making the charge -1. In the same logic, group 16 elements (O, S) need two electrons to get ...
Thu Dec 17, 2020 2:38 am
Forum: Naming
Topic: Determining charge when naming formulas
Replies: 3
Views: 32

### Re: Determining charge when naming formulas

If a coordination compound has a charge, that charge is not included in the actual name. This is an important thing to remember when you are asked to write the formula for a coordination compound after being given the name. You have to make sure to count the charges to determine if the compound as a...
Sun Dec 06, 2020 7:43 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Naming Coordination Compounds
Replies: 7
Views: 63

### Re: Naming Coordination Compounds

For the ions that are not atoms on the periodic table, there are a few that are just helpful to know. CN, for example, is always -1 and NH4 is +1. NH3 is 0, as well as any atoms on their own. Knowing these values are very helpful when attempting to name a compound and calculating the oxidation numbe...
Sun Dec 06, 2020 7:39 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Transition metal number of bonds
Replies: 3
Views: 27

### Re: Transition metal number of bonds

As mentioned in the lecture, we will only be working with transition metals that form up to six bonds. I think, technically, there are some that form many more than this, but it does not look like we will need to concern ourselves with these as of right now. You determine the number of bonds it can ...
Sun Dec 06, 2020 7:32 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Sapling #3 pt. 2
Replies: 5
Views: 39

### Re: Sapling #3 pt. 2

I was also a little confused on this, but I think it is because coordination compounds tend to be more complex and come in pairs to make the compound more stable. Since a seesaw shape has 4 bound atoms and one lone pair, the structure would not be as stable and, as such, is very rare. Since the ques...
Sun Dec 06, 2020 7:26 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Figuring Out monodentate, bidentate, etc
Replies: 5
Views: 38

### Re: Figuring Out monodentate, bidentate, etc

It is essentially how many bonds the ligand can form with the atom. In the case of H20, it is monodentate because the O is the donor atom and there is just one Oxygen. In the case of CH2CH2, though, the donor atom is the Carbon and, since there are two, it is bidentate.
Sun Dec 06, 2020 7:18 pm
Forum: Naming
Topic: Oxidation number
Replies: 5
Views: 49

### Re: Oxidation number

The oxidation number is the more or less the "charge" the atom would have if it was an ion. A good rule of thumb is that nonmetals are usually going to have a negative charge (anions) and metals will have a positive charge (anion). All the metals in group one (the alkaline metals) have a c...
Sun Nov 29, 2020 10:45 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Repulsion Strength
Replies: 1
Views: 13

### Re: Repulsion Strength

Keep in mind that a bond is a pair of shared electrons. As such, they will naturally repulse other electrons around neighboring atoms. This repulsion is what causes the atoms to stay the maximum distance away from each other.
Sun Nov 29, 2020 10:42 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polar/Nonpolar Bonds/Molecules
Replies: 2
Views: 23

### Re: Polar/Nonpolar Bonds/Molecules

Almost every bond is a polar bond. The only exceptions are if the two atoms are the same/have the same electronegativity. A polar molecule is formed when the polar bonds do not cancel out. If you have 2 polar bonds with the same atoms on either side of a central atom, they will cancel out and the mo...
Sun Nov 29, 2020 10:37 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling #3
Replies: 4
Views: 42

### Re: Sapling #3

The bonded pairs are on the axil and the lone pairs are on the equatorial plane. Because they all cancel out, the molecule is nonpolar and also linear.
Sun Nov 29, 2020 10:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: sapling 17 & 18
Replies: 6
Views: 53

### Re: sapling 17 & 18

Hi! Drawing the structures was a little bit harder since sapling was looking for something in particular. As a general rule I would say just play around with the different bond types. First, calculate the number of valence electrons in the molecule. Then, try and form an octet for each atom. After t...
Sun Nov 29, 2020 10:24 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling #7
Replies: 3
Views: 31

### Re: Sapling #7

There is not a guarantee that the atoms will line up across from each other. The way it is written out, it does look as though the polar Cl-C binds and H-Cl bonds line up and are across from each other. However, this isn't necessarily the way they will line up. An H and Cl atom might line up across ...
Sun Nov 15, 2020 7:27 pm
Forum: Octet Exceptions
Topic: Stability of Atoms in 3p
Replies: 3
Views: 40

### Re: Stability of Atoms in 3p

It's not so much the number of electrons that make the molecule more or less stable but the formal charge. For a lot of atoms, this happens to be 8 valence electrons in different configurations of bonded pairs and lone pairs.
Sun Nov 15, 2020 7:20 pm
Forum: Octet Exceptions
Topic: Textbook 2C.3 question
Replies: 3
Views: 41

### Re: Textbook 2C.3 question

I'm not sure if you have to know the formulas for hydrogen phosphate ion or the chloric acid but I would be familiar with phosphate (PO4-3) and chlorate (ClO3-1). There are also a few other ions that are useful to know. But then just know that a hydrogen in front of the name or acid just means that ...
Sun Nov 15, 2020 7:13 pm
Forum: Octet Exceptions
Topic: Group 13 elements
Replies: 5
Views: 48

### Re: Group 13 elements

Since elements in group 13 need 5 electrons to complete the octet and this is very difficult to do as it requires a lot of energy, they can exist in a state without all 8 valence electrons. While most elements exist in their most stable form with 8 valence electrons, elements in group 13 actually ar...
Sun Nov 15, 2020 7:05 pm
Forum: Octet Exceptions
Topic: Nitrogen
Replies: 4
Views: 43

### Re: Nitrogen

Nitrogen, as a general rule, follows the octet rule because it does not have a d orbital. Nitrogen is in the second row which means it only has a s and p orbital. d orbitals do not start until the third orbital. Phosphorus (one row down in the same group as Nitrogen), for example, does have the capa...
Sun Nov 15, 2020 6:57 pm
Forum: Octet Exceptions
Topic: Textbook Question 2C.7
Replies: 3
Views: 20

### Re: Textbook Question 2C.7

It is also better to add the extra electrons to the central atom in order to make it more stable. If the extra electrons were to be added to the surrounding atoms, the electron cloud would be decentralized and, as a result, would be less stable.
Thu Nov 05, 2020 4:27 pm
Forum: Electronegativity
Topic: Periodic Table Trend
Replies: 37
Views: 387

### Re: Periodic Table Trend

The way I think of it is that atomic radius and electronegativity have an inverse relationship. As the atomic radius increases, the electrons stray further away from the nucleus, meaning the protons have less of a pull on them and they are easier to remove. In the same sense, the elements with small...
Thu Nov 05, 2020 4:23 pm
Forum: Octet Exceptions
Topic: "Octets" beyond 8
Replies: 6
Views: 42

### Re: "Octets" beyond 8

I'm not sure what expanding the octet would do for the stability of the molecule in terms of if using the expanded d orbital increases instability, however, I think using the expanded octet would increase the stability of the molecule overall. Elements with an expanded octet usually wither need the ...
Thu Nov 05, 2020 4:19 pm
Forum: Octet Exceptions
Replies: 7
Views: 48

Are radicals only produced when a large amount of energy is provided to make the bonds break? Why doesn't the compound break into two stable molecules instead? As far as I can tell, radicals are usually not present in nature for very long. Because they are so unstable, they seem to be more of an in...
Thu Nov 05, 2020 4:13 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Shortcut for Formal Charge
Replies: 19
Views: 583

### Re: Shortcut for Formal Charge

Since it is a lot of work to write out the formulas every time, I just count up the electrons around an atom in a lewis diagram. Each line counts as 1 (shared/2) and each lone pair counts as 2. Then I just subtract that number from the number of valence electrons and it is easy math you can do in yo...
Thu Nov 05, 2020 4:07 pm
Forum: Formal Charge and Oxidation Numbers
Topic: most stable lewis structure/formal charge
Replies: 6
Views: 66

### Re: most stable lewis structure/formal charge

So I think it is better to form more atoms with formal charges "close to 0" rather than one that is a little further from zero. I think this is because it is better to spread the extra electrons around. While forming a double bond with all the O atoms and S would work (since S can use the ...
Thu Nov 05, 2020 3:54 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic Bonding Question
Replies: 6
Views: 58

### Re: Ionic Bonding Question

The elements on the right (nonmetals) gain electrons, becoming anions (negatively charged). The elements on the left (metals) lose electrons, becoming cations (positively charged). This is because the nonmetals are more electronegative than metals, meaning they hold onto their electrons more tightly...
Thu Oct 08, 2020 8:27 pm
Forum: Balancing Chemical Reactions
Topic: Law of Conservation with Exothermic/Endothermic Reactions
Replies: 11
Views: 131

### Re: Law of Conservation with Exothermic/Endothermic Reactions

Heat does not fall under the Law of Conservation of Mass, so endothermic/exothermic reactions still should have the same number of moles on each side. The confusion here may be coming from the fact that it seems like mass is lost when you burn something, but it is in fact just converted to another s...
Thu Oct 08, 2020 8:22 pm
Forum: Balancing Chemical Reactions
Topic: Fractions
Replies: 14
Views: 108

### Re: Fractions

While it is possible to work with the equations with fractional coefficients, it is not technically proper to do so. During Dr. Lavelle's lecture, he said we should write the equation with whole number stoichiometric coefficients.
Thu Oct 08, 2020 8:20 pm
Forum: Balancing Chemical Reactions
Topic: Periodic Table
Replies: 50
Views: 482

### Re: Periodic Table

I've always been provided a period table of elements during any exams and quizzes I have taken. It does help a lot, however, to know how the table is organized and the trends that go along with it. Especially during timed exams or if there is a question that asks something about which elements are m...
Thu Oct 08, 2020 8:14 pm
Forum: Empirical & Molecular Formulas
Topic: Formula For Nitric Acid F.3
Replies: 3
Views: 51

### Re: Formula For Nitric Acid F.3

I'm not sure how helpful this will be, but I remember it by just knowing that it is an acid so that is where the H comes from. Then the N is obviously there since it is called nitric acid. The oxygen is just a common molecule that goes with that combination so, in my mind, it makes sense that it is ...
Thu Oct 08, 2020 8:13 pm
Forum: Empirical & Molecular Formulas
Topic: Formula For Nitric Acid F.3
Replies: 3
Views: 51

### Re: Formula For Nitric Acid F.3

I'm not sure how helpful this will be, but I remember it by just knowing that it is an acid so that is where the H comes from. Then the N is obviously there since it is called nitric acid. The oxygen is just a common molecule that goes with that combination so, in my mind, it makes sense that it is ...
Thu Oct 08, 2020 7:58 pm
Forum: Empirical & Molecular Formulas
Topic: Rounding up for Empirical Formulas?
Replies: 10
Views: 101

### Re: Rounding up for Empirical Formulas?

You aren't necessarily wrong if you are getting numbers like .8 or .2. It just means you have to plug in different numbers until you find a whole-number multiple. for example, a number with .8 can be multiplied by 5 to equal 4