LikeA'13OSS Posted May 20, 2012 Report Share Posted May 20, 2012 Calculate the pH value of a 0.100 mol/dm3 solution of NaA salt given that the pKa for HA is 8.7 Reply Link to post Share on other sites More sharing options...
CkyBlue Posted May 20, 2012 Report Share Posted May 20, 2012 Convert pKa into Ka. Then do your ICE chart. Ok... I don't really know what your substance is...Ka=[H+][weak acid-] / [weak acid]weak acid>>>H+ +weak acid ion0.1.................0..............00.1-x..............x ...............xKa=x2/(0.1-x)Isolate for x; that's the hydrogen concentration, and then use pH=-log[H+] to find your pH Reply Link to post Share on other sites More sharing options...
LikeA'13OSS Posted May 20, 2012 Report Share Posted May 20, 2012 That would give me the pH of the acid... i want the pH of the salt solution Reply Link to post Share on other sites More sharing options...
CkyBlue Posted May 20, 2012 Report Share Posted May 20, 2012 Oh sorry! Then wouldn't it bepH=pKa+log[ion acid]/[acid]You can use the concentration values you get from the method from my previous post. Reply Link to post Share on other sites More sharing options...
Drake Glau Posted May 20, 2012 Report Share Posted May 20, 2012 Kw=Kb*Kapka of 8.7 is a ka of 10^-8.7We need the kb.Kw=(10^-14) and ka=10^-8.710^-14=kb*10^-8.7kb=5.01^-6Now you can use the equation that Marth said, but you need to use it for bases.kb=x^2/0.15.01^-6=x^2/0.10.0025=[OH-]pOH=-log[OH-]pOH=2.6pH=14-pOH=11.4 Reply Link to post Share on other sites More sharing options...
eelnedross Posted June 21, 2012 Report Share Posted June 21, 2012 Hey, i've got another question.IN both Chemistry and Physics, does "isotope" have the same definition?Also, "isotope" refers to nuclides with the same number of electrons or protons?Thank you! Reply Link to post Share on other sites More sharing options...
Gaby Posted June 21, 2012 Report Share Posted June 21, 2012 Hey, i've got another question.IN both Chemistry and Physics, does "isotope" have the same definition?Also, "isotope" refers to nuclides with the same number of electrons or protons?Thank you!Number of electrons and protons will always be the same in an atom as it has no charge, what differs from isotope to isotope is the number of neutrons in the nucleus, and that's basically the definition of isotopes: atoms of the same element with the same number of protons and electrons but different number of electrons. It's like this in Chemistry, and although I don't study Physics, I see no reason why it would be different there. 1 Reply Link to post Share on other sites More sharing options...
Drake Glau Posted June 21, 2012 Report Share Posted June 21, 2012 (edited) Hey, i've got another question.IN both Chemistry and Physics, does "isotope" have the same definition?Also, "isotope" refers to nuclides with the same number of electrons or protons?Thank you!Number of electrons and protons will always be the same in an atom as it has no charge, what differs from isotope to isotope is the number of neutrons in the nucleus, and that's basically the definition of isotopes: atoms of the same element with the same number of protons and electrons but different number of electrons. It's like this in Chemistry, and although I don't study Physics, I see no reason why it would be different there. They are the same in both subjects.Elements are also "defined" by the number of protons. As far as I know, 2 atoms can be isotopes if they have equal # of protons and differing # of neutrons, regardless of the electron count. Differing electron numbers simply make them ions with +/- charges. Edited June 21, 2012 by Drake Glau 1 Reply Link to post Share on other sites More sharing options...
ananya.agrawal95 Posted July 20, 2012 Report Share Posted July 20, 2012 Hey I'm having a a few problems with some sums in a worksheet we got. Could someone explain how to solve the following questions?Its number 12 and 13 on the linked page - http://isites.harvard.edu/fs/docs/icb.topic1096438.files/PS4.pdf Reply Link to post Share on other sites More sharing options...
Drake Glau Posted July 20, 2012 Report Share Posted July 20, 2012 (edited) I'll do 13 now because I don't want to do math at 1am, sorry. I'll do it later if I remember and no one else gets to it...Graph C is a first order reaction and the slope is -k.B is a zero order and the slope of this line is -k.A is 2nd order and the slope is still k.You can find all of these by looking at your integrated rate laws for the different orders since they all form a straight line due to the integration.Random note: Both of these questions are HL level and some of 13 isn't even required for you to know (what the slope indicates). Just thought I'd share in case you are worried about these types of questions.The integrated rate laws are also provided in your data booklet (I think?) Edited July 20, 2012 by Drake Glau 1 Reply Link to post Share on other sites More sharing options...
ananya.agrawal95 Posted July 20, 2012 Report Share Posted July 20, 2012 Haha This isn't for school Im taking a college credit course in General Chemistry at Harvard so this is my hw for tomorrow. Hopefully it'll make Chem HL easier (starting the IB this august)... Thanks a lot Reply Link to post Share on other sites More sharing options...
Drake Glau Posted July 20, 2012 Report Share Posted July 20, 2012 (edited) Hah, if you can do this already IB chem won't be a problem Edited July 20, 2012 by Drake Glau Reply Link to post Share on other sites More sharing options...
Ana Kraljevic Posted October 21, 2012 Report Share Posted October 21, 2012 Hi guys, i need to write and design investigating one aspect of titration. I have no idea what to do, maybe change the way of determining the pH value, maybe change the concentration idk, obviously i have no idea about chemistry so if anyone could help.. Reply Link to post Share on other sites More sharing options...
SerUmbras Posted October 25, 2012 Report Share Posted October 25, 2012 Hey, i've got another question.IN both Chemistry and Physics, does "isotope" have the same definition?Also, "isotope" refers to nuclides with the same number of electrons or protons?Thank you!Also, it can refer to a molecule with identical molecular formula, but different structural formula. Usually they call it structural/optical/geometerical isomer, but there's still the double meaning, and I screwed that one up once while revising...Hi guys, i need to write and design investigating one aspect of titration. I have no idea what to do, maybe change the way of determining the pH value, maybe change the concentration idk, obviously i have no idea about chemistry so if anyone could help.. One interesting thing that you can is change the pH of the acid/base you're adding (don't know which - doesn't really matter). For example, use HCl and CH3COOH (Ethanoic acid) to titrate the base, and draw a graph plotting the pH on the x-axis against volume added on the y-axis. They do that in the HL questions, so why can't you. Unless someone stands up and says that's a bad idea, I'll stand by that. Reply Link to post Share on other sites More sharing options...
Drake Glau Posted October 25, 2012 Report Share Posted October 25, 2012 (edited) Hey, i've got another question.IN both Chemistry and Physics, does "isotope" have the same definition?Also, "isotope" refers to nuclides with the same number of electrons or protons?Thank you!Also, it can refer to a molecule with identical molecular formula, but different structural formula. Usually they call it structural/optical/geometerical isomer, but there's still the double meaning, and I screwed that one up once while revising...Isotope and isomer are not the same thing O.oIdk if your quoted question has been answered sooo to the person posting the question, isotopes have the same number of e- and protons, different number of neutrons thus yielding a different molecular mass for the same element. You will see this in physics when you get to radioactivity. U-235 and U-238 were the big ones if i remember right. Edited October 25, 2012 by Drake Glau Reply Link to post Share on other sites More sharing options...
SerUmbras Posted November 2, 2012 Report Share Posted November 2, 2012 Hey, i've got another question.IN both Chemistry and Physics, does "isotope" have the same definition?Also, "isotope" refers to nuclides with the same number of electrons or protons?Thank you!Also, it can refer to a molecule with identical molecular formula, but different structural formula. Usually they call it structural/optical/geometerical isomer, but there's still the double meaning, and I screwed that one up once while revising...Isotope and isomer are not the same thing O.oIdk if your quoted question has been answered sooo to the person posting the question, isotopes have the same number of e- and protons, different number of neutrons thus yielding a different molecular mass for the same element. You will see this in physics when you get to radioactivity. U-235 and U-238 were the big ones if i remember right. I realised this a few days after posting and knew that someone would say something. Thanks for clarifying... Reply Link to post Share on other sites More sharing options...
CallMeTheBean Posted December 21, 2012 Report Share Posted December 21, 2012 Can somebody help me with an alpha decay equation? I want to alpha decay Fluorine-18. Reply Link to post Share on other sites More sharing options...
Drake Glau Posted December 21, 2012 Report Share Posted December 21, 2012 (edited) Alpha Decay is the removal of a Helium atom. 2 protons and 2 neutrons, total mass of 4. So your atomic number would drop by 2 (2 protons) and your mass number by 4 giving you N-14F-18 -> He-4 + N-14The He-4 can be replaced with a alpha letter if you like Edit to clarify "removal"...a Helium particle is ejected from the original particle due to energy and proper circumstances. Removal just sounded funny to me... Edited December 21, 2012 by Drake Glau Reply Link to post Share on other sites More sharing options...
Ushiie Posted January 3, 2013 Report Share Posted January 3, 2013 In our school we have to teach ourselves the entire Biochemistry Unit and I am having trouble in finding out which topics I should focus the most on. Do you guys have any tips? Reply Link to post Share on other sites More sharing options...
Sandwich Posted January 3, 2013 Report Share Posted January 3, 2013 In our school we have to teach ourselves the entire Biochemistry Unit and I am having trouble in finding out which topics I should focus the most on. Do you guys have any tips?Grab the syllabus, look up the Biochemistry section and focus on all of it If you just learn exactly from your textbook what it states you should on the syllabus, to the extent suggested on the syllabus, you'll be fine. The application aspects of things can be a little tricky to interpret from the syllabus, but for that flick through some past papers to see what sorts of questions they like to ask. Reply Link to post Share on other sites More sharing options...
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