Search found 26 matches

by Golbarg Rahimi 3k
Sun Dec 10, 2017 10:44 pm
Forum: Administrative Questions and Class Announcements
Topic: Final [ENDORSED]
Replies: 4
Views: 910

Re: Final [ENDORSED]

Couldn’t we just say that since the products would be salt and water and salt is solid then the ph would equal the ph of water that is 7?
by Golbarg Rahimi 3k
Sun Dec 10, 2017 6:08 pm
Forum: Administrative Questions and Class Announcements
Topic: Final [ENDORSED]
Replies: 4
Views: 910

Final [ENDORSED]

Hi, Didn’t Dr lavelle mention that salts were not going to be included in our final due to the fire? Question 8a was asking for the PH of a solution containing both NaOH and HCl which produced nacl salt. Were we supposed to know how to solve this problem without the knowledge on salts? If so how cou...
by Golbarg Rahimi 3k
Sun Dec 10, 2017 3:12 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Exam HCl and NaOH question?
Replies: 3
Views: 400

Re: Exam HCl and NaOH question?

I had trouble with this question as well since we did not cover questions with 2 strong acid and base mixed together and their PH. It also wasn’t in our homeworks. Or at least I can’t remember it being discussed in the lectures.
by Golbarg Rahimi 3k
Sun Dec 10, 2017 8:30 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 11.115 (f) equilibrium shift
Replies: 1
Views: 208

11.115 (f) equilibrium shift

In the online exercises, adding water is like adding a reactant and makes the equilibrium shift to the right. However in question 11.115, adding water has no effect on the equilibrium. Both equations have the same states. Liquid water and aq product. So how does water affect equilibrium?
by Golbarg Rahimi 3k
Sat Dec 09, 2017 1:25 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Homework 4.13
Replies: 3
Views: 214

Re: Homework 4.13

Why doesn’t the double bond in this question affect the bond angle?
by Golbarg Rahimi 3k
Sat Dec 09, 2017 8:11 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination number [ENDORSED]
Replies: 1
Views: 129

Coordination number [ENDORSED]

Is the coordination number the number of bonds only in the coordination sphere? If the coordination compound is a cation or anion and is attached to an anion or cation, does that bond count in the coordination number if it is not in the sphere?
by Golbarg Rahimi 3k
Fri Dec 08, 2017 7:40 am
Forum: Lewis Acids & Bases
Topic: HF
Replies: 4
Views: 229

Re: HF

In our book it states that in these molecules as we go across a period we have to consider electronegativity but as we go down a group we have to consider bond length and the radius. So we compare HCL and HF based on their radius since they are in the same group. Cl has a larger radius and more acidic
by Golbarg Rahimi 3k
Wed Dec 06, 2017 3:21 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.13 (b)
Replies: 1
Views: 106

4.13 (b)

The lewis structure of POCl3 is tetrahedral but p has an expanded octet and a double bond. Why doesn't the double bond affect the bond angles? I was thinking that because of the double bond the angle has to be less than 109.5 but in the solution manual the angles are 109.5. thanks
by Golbarg Rahimi 3k
Thu Nov 30, 2017 12:31 pm
Forum: Hybridization
Topic: 4.95
Replies: 3
Views: 203

Re: 4.95

The hybridization for oxygen is sp2 since it has 3 regions of electron density surrounding it. two regions of electron density are the lone pairs and the third region is the double bond. double bonds count as one region of electron density. we use 2sp2 when we want to specify the actual orbitals inv...
by Golbarg Rahimi 3k
Thu Nov 30, 2017 12:25 pm
Forum: Ideal Gases
Topic: Temperature in PV=nRT
Replies: 9
Views: 511

Re: Temperature in PV=nRT

We have to use Kelvin temperature since in this formula T could be at the denominator. If we were using Celsius unit, then we would have had zero at the denominator at some point. Because a zero denominator does not give us a solution, we use kelvin. when kelvin is zero that suggests we have an abso...
by Golbarg Rahimi 3k
Thu Nov 23, 2017 3:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.43
Replies: 1
Views: 140

Re: 11.43

for this question, you have to draw the ICE table. the initial pressure of the reactant is 1. Its stoichiometry coefficient is 2 and if we consider the change of the products as X, the change NO undergoes would be -2X. so the pressure at equilibrium for NO would be (1-2x) and X for each of the produ...
by Golbarg Rahimi 3k
Thu Nov 23, 2017 3:34 pm
Forum: Hybridization
Topic: Valence/valency?
Replies: 1
Views: 116

Re: Valence/valency?

the valence number is the number of electrons located in the outer layer of the atom ( valence shell). These electrons can form bonds with other atoms, therefore they should not be paired. carbon has the electron configuration of (he)2s22p2 this means that there are 2 unpaired electrons in the outer...
by Golbarg Rahimi 3k
Thu Nov 16, 2017 5:42 pm
Forum: Hybridization
Topic: Significance of Hybridization
Replies: 3
Views: 181

Re: Significance of Hybridization

Also, I think hybridization lowers the energy of the orbitals thus creating a compound that is more stable.
by Golbarg Rahimi 3k
Thu Nov 16, 2017 5:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.25 lewis structure
Replies: 4
Views: 187

Re: 4.25 lewis structure

since F and Cl both belong to the same group and are both halogens the lewis structure would be the same.
by Golbarg Rahimi 3k
Wed Nov 08, 2017 11:20 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant
Replies: 3
Views: 240

Re: Limiting Reactant

Another strategy that seems to work when comparing moles is figuring out the number of moles for each compound and dividing it by its stoichiometric coefficient. At this point, we could compare the 2 numbers. The smaller number is the limiting reactant.
Moles
————-
Coefficient
by Golbarg Rahimi 3k
Wed Nov 08, 2017 10:32 pm
Forum: Balancing Chemical Reactions
Topic: Net Moles of Gas
Replies: 5
Views: 254

Re: Net Moles of Gas

If we have 4 moles of C4H10 that would result in 26 moles o2, 16 moles co2 and 20 moles H2o.
4+26=30
16+20=36
The difference in the gases which is the net gas produced is 36-30=6
In this equation we consider all of the states as gas since the temperature is very high and the water evaporates.
by Golbarg Rahimi 3k
Thu Nov 02, 2017 10:43 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Writing Electron Configurations for ions
Replies: 2
Views: 161

Re: Writing Electron Configurations for ions

if you start by writing the electron configuration of Cu in its ground state, you will have [Ar]3d104s1
now if you take one electron away from the outer shell to get the ion, you will have [Ar]3d10.
by Golbarg Rahimi 3k
Thu Nov 02, 2017 8:48 pm
Forum: Trends in The Periodic Table
Topic: Carbon vs. Nitrogen Ionization Trend
Replies: 3
Views: 179

Re: Carbon vs. Nitrogen Ionization Trend

nitrogen has an ionization energy of 1400 kJ/mol while carbon has an energy of 1086 kJ/mol. Therefore as expected, nitrogen has higher energy than carbon. There is an irregularity in their electron affinity.
by Golbarg Rahimi 3k
Thu Oct 26, 2017 10:05 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: s- electrons vs p- electrons [ENDORSED]
Replies: 7
Views: 403

Re: s- electrons vs p- electrons [ENDORSED]

Basically, the s orbitals have fewer electrons standing between them and the nucleus, therefore, they are less shielded. The p orbitals are more shielded than the s orbitals of the same shell.that is why p orbitals have higher energy.
by Golbarg Rahimi 3k
Thu Oct 26, 2017 9:23 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 2.1
Replies: 2
Views: 179

Re: 2.1

Hi
You need to look at each separately
a) energy of electron increases as we increase n from 1 to 2
b) we are going from 1s to 2p so n is increasing
c) the s orbital has l=0 and the p orbital has l=1 so it is increasing
d) radius of atom increases when n increases
by Golbarg Rahimi 3k
Wed Oct 18, 2017 2:34 pm
Forum: Properties of Electrons
Topic: Energy Levels
Replies: 3
Views: 243

Re: Energy Levels

the electron could absorb energy and go to a higher level or emit energy and go to a lower level. The equation En=-hR/n2 simply calculates the energy of the specific level and it has nothing to do with the previous energy level. the difference between energy levels is calculated with deltaE= Efinal-...
by Golbarg Rahimi 3k
Wed Oct 18, 2017 2:22 pm
Forum: DeBroglie Equation
Topic: 1.37 [ENDORSED]
Replies: 5
Views: 318

Re: 1.37 [ENDORSED]

Hi
I think their masses would be given on a separate sheet attached to the exam paper.
by Golbarg Rahimi 3k
Thu Oct 12, 2017 4:18 pm
Forum: Einstein Equation
Topic: Einstein
Replies: 4
Views: 275

Re: Einstein

Hi
Einstein discovered the concept of the photon however Gilbert Lewis, an american chemist, named it photon.
by Golbarg Rahimi 3k
Thu Oct 12, 2017 4:01 pm
Forum: Properties of Light
Topic: Prefix Conversion
Replies: 12
Views: 513

Re: Prefix Conversion

Hi
I tend to convert all the units into SI units or to common chemistry units ( s , m, g) before trying to solve the problem. After the problem has been solved, I convert them back to the desired units in the problem.
by Golbarg Rahimi 3k
Thu Oct 05, 2017 9:11 pm
Forum: Molarity, Solutions, Dilutions
Topic: E. 23
Replies: 2
Views: 327

Re: E. 23

you have 3.00 grams of CuBr2 with the molar mass of 223.35. by dividing them you get the moles of CuBr2 available. each mole of CuBr2 has 1 mole of Cu ions.
therefore the number of moles of CuBr2 equal the number of moles of Cu ions .
by Golbarg Rahimi 3k
Thu Oct 05, 2017 9:00 pm
Forum: Limiting Reactant Calculations
Topic: L39 .. I don't understand it. May someone please explain it to me?! Thank You.
Replies: 2
Views: 262

Re: L39 .. I don't understand it. May someone please explain it to me?! Thank You.

By subtracting 26.45 from 28.35 ( 28.35-26.45=1.90) you will have the actual grams of product formed. you already know that the product is made of tin ( Sn) and Oxygen. with the initial amount of tin available ( 1.50g) you can determine the moles of tin available and produced. we have 1.90 grams of ...

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