Heat of a Reaction
Updated: 2010-09-03 04:17:55
The heat of a reaction is measured in a bomb calorimeter. This heat is equal to which thermodynamic quantity?A) EB) GC) HD) SWhy is the answer A instead of C?
Percent Dissociation of HA
Updated: 2010-09-03 04:03:48Hi...I'm confused about the % Dissociation on the attached problem:What is the percent dissociation of HX? (image attached) Our book defines percent dissociation as HA dissociated / HA initial * 100 is the % HA dissociated. But when I use that formula for the HX reaction, my answer is wrong. (4 dissociated / 10 initial = 40%) Please *delete me* I don't know the molarity in the problem so I was just using the number of molecules.Re: Electrochemistry Questions
Updated: 2010-09-03 04:02:251. Would the other equation be 4F- + 2H2O 4HF + O2 then?2. So you mean the sulfate ion being replaced by water?And thank you very very much for the *delete me*Why isn't [water] included in the ion-product expression for water?
Updated: 2010-09-03 03:51:17The common answer (and the one in my text book) to this is that the "concentration" of the water in the solution varies so little that it can be considered constant and is therefore incorporated into the equilibrium constant. However, in writing Kc expressions for other reactions, the reason for not including a liquid or solid in the equilibrium expression is that the concentration of a solid or a pure liquid cannot change. This seems to imply that in the case of the auto-ionization of water, the concentration of water changes but it ignored and that in other reactions, the concentration of pure water does not change at all.Have I understood this correctly or have I gone wrong somewhere?Re: Atoms in an Alloy. Where did I mess up?
Updated: 2010-09-03 03:19:00It happens, I usually find one or two errors in textbooks. The most common cause is that the question starts out as 'Find the no. of atoms of Zn...' but gets changed later because an editor thinks it is too easy/difficult and, in the rush to get things published, someone forgets to check the answer was changed accordingly.I'm actually quite in awe of the relatively few mistakes that copy editors let through in a publication the size of a textbook. When you come to write your dissertation/thesis, you'll find it's remarkably difficult to find them all.Cutting-Edge C&EN Webinars, Coming Soon
Updated: 2010-08-31 20:45:00
The program of C&EN Webinars on cutting-edge research topics continues to broaden; you can register now for any of these upcoming sessions: Core Technologies for Chiral & Specialty Intermediates for Pharma (Thursday, September 9, 10:00 a.m. EDT); Hopscotch and Jump Rope - get lead hops, scaffold hops, and step-jumps in potency, with unique computational strategies for molecular design (Thursday, September 16, 11:00 a.m. EDT); or Stabilized Lithium Metal Powder (SLMP): A New Approach for Energy Storage and Other Applications (Thursday, September 23, 9:00 a.m. EDT).ACS Careers Job Club Webinars
Updated: 2010-08-31 20:45:00Log In ACS Journals C EN CAS ACS Network Store Governance About Us Contact Publications Meetings Careers Membership Networks Education Policy Funding Awards Press Room American Chemical Society Careers Job Search Starting a Job Club Job Clubs Provide Support for Your Job Search Job Clubs Provide Support for Your Job Search If You Can’t Find One That’s Right for You , Start Your Own Misery Loves Company An informative article on Job Clubs by an ACS . expert Other Job Club : Resources Job Club Webinar Series Job Search Strategies Webinar wmv file 53 MB Preparing Your Resume Webinar wmv file 59 MB Effective Interviewing Webinar wmv file 52 MB ACS Career Series Videos Planning My Job Search wmv file 67 MB The Group Discussion Guide Facilitators Discussion Guide Resumes wmv file 58 MB The GroupO Level Chemistry: Molecular & Empirical Formulae
Updated: 2010-08-31 05:30:34
For all students learning O Levels Chemistry (and other equivalents), it is important that you understand the difference between the 3 types of formulae commonly used – namely Molecular Formula, Empirical Formula and Structural Formula.
Previously, we have discussed on this topic before. You can find them HERE.
Let’s define them now, for better understanding and application:
Molecular [...]O Level Chemistry: Air (Atmosphere)
Updated: 2010-08-24 02:47:56Air or some like to call it Atmosphere is considered a ‘minor’ chapter in GCE O Levels Chemistry examination, so much so that many teachers do not emphasise on their existence, not to mention importance.
As described by my Sec 4 Chemistry students, many of their Chemistry School teachers:
Ask the students to read textbook on their [...]O Level Chemistry: Mole Calculation Question & Common Mistakes Made
Updated: 2010-08-22 03:30:33The following Mole Calculation question is not difficult but many O Levels Chemistry students tends to make mistake in exams, where time is not a luxury. When the same question was posed to my regular classes of Sec 3 and 4 O Levels and IP students, i realised that many fall into the trap also.
Let’s [...]O Level Chemistry: Challenging Mole Calculation / Electrolysis Questions
Updated: 2010-08-14 01:29:34In the previous post, we have discussed on a MCQ question on Electrolysis that requires students to:
1. Write out discharge half equations
2. Do Molar Ratio Comparisons
Question:
Which of the following requires the least number of eletrons for discharge?
A. 2 mol of Al3+ (aluminium) ions
B. 5 mole of OH- (hydroxides) ions
C. 3 mol of O2- (oxides) ions
D. [...]O Level Chemistry: Challenging Mole Calculation / Electrolysis Questions
Updated: 2010-08-12 06:28:27In the previous post, we have discussed on 1 MCQ question on Electrolysis that requires basic Mole Calculations strategy to solve.
Do note that Electrolysis topic is only applicable to students taking:
GCE ”O” Level Pure Chemistry (Code: 5072)
Integrated Programme (IP) – it will be classified under Electrochemistry chapter
IB programme
IGCSE and other equivalents
It is NOT applicable to [...](Visible) scars of chemistry
Updated: 2010-08-02 06:03:48
Mitch’s post showing the video of “the mark of the chemist” reminds me of one of the most visible remembrances I have of graduate school: the scar on one of my middle fingers (see left.) On a lovely Saturday in the lab (my music playing, no one else around), I dropped a Dewar flask from [...]Dangerous Chemistry Sets
Updated: 2010-07-26 23:23:02
From: SMBC – Fear Itself ~MitchCargo cult science in the Gulf, news at 11
Updated: 2010-07-21 06:34:32
The Gulf oil tragedy has already shown the ignorance of some reporters about chemistry. However, a Mobile TV station and their chemist has taken it to new heights when they blamed the oil spill for (likely) bad glassware. WKRG is a local TV news station in Mobile, Alabama; they sent intrepid reporter Jessica Taloney to [...]Common Student Difficulties in Organic Chemistry
Updated: 2010-07-13 15:51:43
While cleaning out my newly assigned “war room” (the setting where I’ll strategize on how best to torture students this fall), I came across some fairly interesting documents that were buried in far corners of crowded file cabinets. They’re nothing personal or discriminating (sorry TMZ), but I saw them as material I could use in [...]Chemists Purposely Withholding Information
Updated: 2010-07-09 16:57:23I once saw an undergraduate setting up a reflux in my lab, and I could tell immediately it wasn’t going to work. The undergraduate didn’t take enough precautions to ensure that the liquid wouldn’t leak out from the joint connecting the round bottom flask and the condenser. I debated whether I should say anything, but [...]Your Academic Lineage
Updated: 2010-07-05 16:45:30Over dinner the other night, my uncle and I started comparing and contrasting our academic experiences. He’s a fascinating person who earned a bachelor’s degree in computer science in the late 1970’s. After discussing the finer points of Moore’s Law, and how he agonized over purchasing a 20 MB hard drive in the 1980’s for [...]