Search found 35 matches

Wed Dec 05, 2018 7:52 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: HW 7th edition 6B.9
Replies: 3
Views: 155

Re: HW 7th edition 6B.9

I had the same question... both part i) and part ii) run into the same problem, where taking the negative log of 1.50 gives -0.176 instead of positive 0.176. Anyone have an idea what's happening?
Wed Dec 05, 2018 6:30 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: HW: 6B.1 (7th)
Replies: 1
Views: 116

HW: 6B.1 (7th)

"The molar concentration of HCL in hydrochloric acid is reduced to 12% of its initial value by dilution. What is the difference in the pH values of the two solutions?" I'm having trouble understanding how to start with this problem and how pH and dilution relate to each other. How do you c...
Wed Dec 05, 2018 6:00 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Equilibrium constants
Replies: 1
Views: 107

Equilibrium constants

In general, what are equilibrium constants and what is their significance? Also, what is Kw (the autoprotolysis constant according to the textbook), and what do we need to know about it for the final? Finally, what is the difference between Kw and Ka? Thanks in advance.
Mon Dec 03, 2018 4:26 pm
Forum: Bronsted Acids & Bases
Topic: Fundamentals J.17 (7th)
Replies: 2
Views: 218

Fundamentals J.17 (7th)

The question says to identify either a weak acid or a weak base in each compound and write the chemical equation for its reaction with water. How do you know which molecule is a weak base/weak acid just based on the formula? For example, part d has the formula NH4Br, and the answer is that NH4 is a ...
Wed Nov 28, 2018 3:43 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic/Covalent bond cut offs
Replies: 1
Views: 125

Re: Ionic/Covalent bond cut offs

If the electronegativity difference is greater than 2, then the bond is ionic. If the difference is less than 1.5, then the bond is covalent.
Wed Nov 28, 2018 3:23 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Identifying intermolecular forces
Replies: 4
Views: 185

Re: Identifying intermolecular forces

Remember that intermolecular forces are not within molecules; they are between different molecules, and include dipole-dipole, hydrogen bonds, and London dispersion forces. Intramolecular forces are the ones that are within molecules, and they include ionic and covalent bonds.
Wed Nov 28, 2018 1:32 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond angles of See Saw
Replies: 2
Views: 377

Bond angles of See Saw

According to an answer in the textbook (2E.11 a), the bond angles for a see saw shape (SCl4) are the same as those for trigonal bipyramidal- 120 and 90 degrees. Shouldn't the angles be slightly less because of the lone pair?
Wed Nov 28, 2018 12:55 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: 3F.5 part b (7th Ed.) Melting point
Replies: 4
Views: 187

3F.5 part b (7th Ed.) Melting point

This problem asks which has the higher melting point, C2H5OC2H5 (diethyl ether) or C4H9OH (butanol). The answer is butanol, but I don't understand why. Anyone know?
Mon Nov 26, 2018 9:11 pm
Forum: Sigma & Pi Bonds
Topic: 2F.17 7th ed: Pi bond
Replies: 2
Views: 136

2F.17 7th ed: Pi bond

Why is there a pi bond in CH2O? I understand that there are 3 sigma bonds because there are 3 single bonds, but I don't get where the pi bond comes in. How do you know when there is a pi bond?
Sun Nov 25, 2018 11:47 pm
Forum: Sigma & Pi Bonds
Topic: Hybridization and Electron Configurations
Replies: 3
Views: 173

Hybridization and Electron Configurations

When stating the hybridization of a specific atom in a given molecule, is it necessary to draw out the electron configuration for the atom, including the pairings of the electrons in each orbital, like prof. Lavelle did in class?
Sun Nov 25, 2018 9:53 pm
Forum: Sigma & Pi Bonds
Topic: Number of sigma and pi bonds
Replies: 5
Views: 477

Number of sigma and pi bonds

Can someone explain how to figure out the number of sigma and pi bonds in a molecule just by knowing the number of hybridized orbitals on the central atom? For example, in problem 2F.3 I know that the central atom, S, has four hybridized sp3 orbitals. How do I know the sigma/pi bonds from that?
Mon Nov 19, 2018 11:37 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E.25 (7th Ed.) Lewis structure and polarity
Replies: 2
Views: 95

2E.25 (7th Ed.) Lewis structure and polarity

We learned that the polarity of a molecule can depend on the shape, since partial charges can cancel each other out. But for this problem, the answer says that CH2Cl2 is polar because the Lewis structure is drawn with the chlorine atoms on one side and the hydrogen atoms on the other. But wouldn't w...
Sun Nov 18, 2018 7:47 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pairs
Replies: 3
Views: 138

Re: Lone Pairs

Lone pairs have a more strongly repelling effect than do bonding pairs. So, when there are lone pairs the bonding pairs are pushed closer together, decreasing the bond angles between them. These bond angles are experimentally determined.
Sun Nov 18, 2018 7:43 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining Shape
Replies: 5
Views: 248

Re: Determining Shape

Yes, it is based on the lone pairs around the central atom which distort the shape. For example, trigonal planar and trigonal pyramidal both have the same number of regions of electron density (3), but we can distinguish between them because a trigonal pyramidal shape has a lone pair which pushes th...
Mon Nov 12, 2018 7:40 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 7th Ed. 2.7: Most important Lewis structure
Replies: 2
Views: 141

7th Ed. 2.7: Most important Lewis structure

The question says to draw the "most important Lewis structure" for N5+, including all equivalent resonance structures. What does it mean by most important? Also, why is the most important structure the one with a -1 charge on the central atom instead of a 0 charge?
Sun Nov 11, 2018 3:02 pm
Forum: Bond Lengths & Energies
Replies: 3
Views: 216

What exactly is the covalent radius of an atom and how is it different from its atomic radius?
Sun Nov 11, 2018 2:41 pm
Forum: Dipole Moments
Topic: Polarizable vs Polarizing Ability
Replies: 3
Views: 202

Re: Polarizable vs Polarizing Ability

In general, large anions are highly polarizable because the nucleus' pull on the outermost electrons is smaller due to the size of the anion, so the electron cloud is easily distorted. You can think of it as the electrons not being held very tightly by the nucleus, causing them to be pulled in diffe...
Sun Nov 11, 2018 2:29 pm
Forum: Dipole Moments
Topic: Solubility in Water
Replies: 5
Views: 267

Solubility in Water

Can someone summarize how solubility in water is related to the size, electric dipole moments, and ionic/covalent character of molecules? Are there any other factors that affect solubility? Why are silver halides (AgF, AgCl, AgBr, and AgI) less soluble specifically?
Sun Nov 04, 2018 1:33 pm
Forum: Lewis Structures
Topic: 7th Ed. 2C.3 Part B: Lewis structure
Replies: 1
Views: 125

7th Ed. 2C.3 Part B: Lewis structure

For the Lewis structure of hydrogen phosphate ion, the solution shows P in the center with three O and one OH attached to it. My question is, why did they put OH together as one atom instead of connecting O and H with a bond? Is this how compounds are normally arranged? How would you know to do this...
Sat Nov 03, 2018 10:00 pm
Forum: Lewis Structures
Topic: Formal Charges on Midterm
Replies: 2
Views: 116

Formal Charges on Midterm

On the midterm, when we draw Lewis Structures will we have to write the formal charges next to each element in the structure? Also, is it okay to calculate the charges in our head instead of writing them out?
Thu Nov 01, 2018 2:59 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: S and d orbitals order in configuration
Replies: 2
Views: 157

S and d orbitals order in configuration

I'm a little confused about the general rule for the order to fill in orbitals. Normally, is it correct to fill in the f and d-orbitals first (if there are any), then fill in the s and p orbitals? If you do this, the configuration tends to go in order of increasing n values (ex. 4f^14 5d^10 6s^2 6p^...
Wed Oct 24, 2018 3:45 pm
Forum: Photoelectric Effect
Topic: Module question 30 c
Replies: 4
Views: 230

Re: Module question 30 c

Thank you, it did help! I was overthinking the equations. But, now I got 150.6 J for question 29b when I added the work function plus my answer from 28a. I then used frequency=E/h and got 2.27 x 10^35. However, the answer seems to be to the power of 38. Do you know why I get the wrong power sometim...
Mon Oct 22, 2018 7:53 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg Indeterminacy Post Assessment #20
Replies: 2
Views: 160

Heisenberg Indeterminacy Post Assessment #20

"Use the above uncertainty in velocity to calculate the electron's uncertainty in kinetic energy. Then calculate the uncertainty in kinetic energy per mole of electrons (that is, per mole of hydrogen atoms). Comment on your value." How do you find uncertainty in kinetic energy? As far as I...
Mon Oct 22, 2018 6:58 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg Indeterminacy Post Assessment #18
Replies: 1
Views: 127

Heisenberg Indeterminacy Post Assessment #18

"The hydrogen atom has a radius of approximately 0.05 nm. Assume that we know the position of an electron to an accuracy of 1 % of the hydrogen radius, calculate the uncertainty in the speed of the electron using the Heisenberg uncertainty principle. Comment on your value obtained." What d...
Fri Oct 19, 2018 2:57 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Shielding in Multi-Electron Atoms (1E.5)
Replies: 1
Views: 63

Shielding in Multi-Electron Atoms (1E.5)

Are electrons with lower values of l (i.e. l=1) always better at shielding than electrons with higher values of l (i.e. l=2)? In other words, would an electron in the p-orbital be more effective at shielding than would an electron in the d-orbital? If so, why? Does this have to do with penetration t...
Thu Oct 18, 2018 10:58 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Wave Functions
Replies: 2
Views: 70

Re: Wave Functions

The wave function is a value that describes the position of the electron in the atom. The squared wave function value is equal to the probability of finding the electron in a region (probability density).
Sat Oct 13, 2018 4:22 pm
Forum: Photoelectric Effect
Topic: Threshold energy [ENDORSED]
Replies: 17
Views: 849

Re: Threshold energy[ENDORSED]

Threshold energy doesn't factor into calculating the energy per photon, but it does factor into calculating the kinetic energy, or the excess energy from the electron being ejected. The kinetic energy is equal to the energy of the incoming photon minus the threshold energy (energy required to eject ...
Sat Oct 13, 2018 2:33 pm
Forum: Photoelectric Effect
Topic: 1B.9: Trouble with exponents and units
Replies: 3
Views: 189

1B.9: Trouble with exponents and units

A lamp rated at 32 W emits violet light of wavelength 420 nm. How many photons of blue light can the lamp generate in 2.0 s? How many moles of photons are emitted in that time interval? For this problem, I tried using v=C/λ to find the frequency, then multiply that by two seconds to get the number o...
Mon Oct 08, 2018 11:40 pm
Forum: Properties of Light
Topic: Problem 1B.5: Units KeV
Replies: 2
Views: 68

Problem 1B.5: Units KeV

This question is asking for you to calculate the wavelength of y-rays, and you are given the energy of the photons: 140.511 keV. Does anyone know what the unit keV means and how to use it in an equation? I tried using E=hv to find frequency and then using C= λv to find the wavelength. But I got stuc...
Sun Oct 07, 2018 8:40 pm
Forum: Properties of Light
Topic: Formula for energy of a photon
Replies: 4
Views: 101

Formula for energy of a photon

Where in the book (7th ed.) can I find the formula for calculating energy of a photon? A question requires you to use it but I can't seem to find it anywhere.
Sun Oct 07, 2018 8:35 pm
Forum: Properties of Light
Topic: 1A.15: Initial and final energy levels
Replies: 1
Views: 55

1A.15: Initial and final energy levels

I don't understand how to figure out the values of n for the final energy level of a specific line with a given wavelength. I know that this line (102.6 nm) is in the Lyman series according to figure 1A.10, so it makes sense that the initial value would be n=1, but how do you know what the final ene...
Thu Oct 04, 2018 3:05 pm
Forum: Molarity, Solutions, Dilutions
Topic: Deteremining V1 vs. V2
Replies: 1
Views: 127

Re: Deteremining V1 vs. V2

I completely understand, some dilution problems can be worded very confusedly. One thing that helps me make sense of a problem when I first look at it is to write down all the given numbers and what exactly they are according to the equation M1V1=M2V2. For example, I would write the volume given for...
Thu Oct 04, 2018 2:54 pm
Forum: SI Units, Unit Conversions
Topic: pm to m
Replies: 6
Views: 486

Re: pm to m

It is true that the textbook doesn't list the pico prefix in the table, but it shouldn't be too hard to remember since the conversion exponents decrease by threes (-3 to -6 to -9 to -12). Just remember that picometers are the smallest units and right after nanometers so the conversions exponent is -...
Tue Oct 02, 2018 11:18 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Exercise E9
Replies: 3
Views: 172

Re: Exercise E9

I think the tricky part about this problem is the formula for Epsom salt, which is MgS04.7H20 (the "." is supposed to represent the notation for hydrates, but I couldn't figure out how to type it out). The problem states that epsom salt is magnesium sulfate heptahydrate, which means that ...
Mon Oct 01, 2018 5:48 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Exercise E9
Replies: 3
Views: 172

Exercise E9

I'm having trouble with exercise E9, about epson salts. I try to calculate the number of atoms of oxygen, mainly by following the method described in example E2, but I keep getting a different answer than the book. I'm also not sure how to calculate the number of formula units. Can anyone help me out?