kiwi.at.heart Posted October 17, 2011 Report Share Posted October 17, 2011 Hi, I have the atomic structure topic test (only SL material so far) on tuesday.Could someone explain/answer this question? "Y is radioactive, decaying by beta emission.When a sample of the product from the beta decay of Y was passed into a mass spectrometer it produced only one peak, at m/z = 35 whereas a naturally occurring sample of this element gave an extra peak at m/z = 37.Account for this difference between the sample of the element made from Y and the naturally occurring sample of the same element."Thanks.When an element emits beta emission, it has to many neutrons to be stable and the neutrons decay which causes electrons to be ejected. This means that once the element had finished decaying as in the question, it will have less neutrons than the average as it has reduced the number of neutrons in its nuclei to be stable. Naturally occurring would peak at 37 because it hasn't fully decayed and would contain more neutrons than the decayed sample. I could probably word this better for a real answer but I hope this explains it. Reply Link to post Share on other sites More sharing options...
Peanut Butter Jelly Posted October 17, 2011 Report Share Posted October 17, 2011 When looking at a mass spectrum, the isotopes are sometimes shown to be 100% abundant... How can that be if there are more than one isotope?Thanks.i think you mean relative abundant, in which case the most common isotope is 100% relative abundant, Reply Link to post Share on other sites More sharing options...
Drake Glau Posted October 21, 2011 Report Share Posted October 21, 2011 When looking at a mass spectrum, the isotopes are sometimes shown to be 100% abundant... How can that be if there are more than one isotope?Thanks.i think you mean relative abundant, in which case the most common isotope is 100% relative abundant,This is correct. It's all relative to the most abundant so it is 100% and the other percentages are based off of it. So it's not saying 80% of the isotopes are B and 100% of them are A (that doesn't even make sense), it's more like saying 80% of isotope A's total number is isotope B. Reply Link to post Share on other sites More sharing options...
jonathan810 Posted October 22, 2011 Report Share Posted October 22, 2011 (edited) Chloroethene reacts with oxygen according to the equation below:2C2H3Cl(g)+5O2(g) -> 4CO2(g)+2H2O(g)+2HCl(g)what is the amount in mol, of H2O produced when 10.0 mol of C2H3Cl and 10.0 mol of O2 are mixed together, and the above reaction goes to completion?A: 4.00B: 8.00C: 10.0D : 20.0 Edited October 22, 2011 by jonathan810 Reply Link to post Share on other sites More sharing options...
Lero Posted October 22, 2011 Report Share Posted October 22, 2011 Chloroethene reacts with oxygen according to the equation below:2C2H3Cl(g)+5O2(g) -> 4CO2(g)+2H2O(g)+2HCl(g)what is the amount in mol, of H2O produced when 10.0 mol of C2H3Cl and 10.0 mol of O2 are mixed together, and the above reaction goes to completion?A: 4.00B: 8.00C: 10.0D : 20.0Since you have 10 moles of each reactant then all of the 10 moles of oxygen will be used up but only 4 moles of chloroethene are used (limiting reagent).Then since 10 moles of oxygen and 4 moles chloroethene used, then it follows that 4 moles of water are produced. A. 1 Reply Link to post Share on other sites More sharing options...
lullabyy Posted October 23, 2011 Report Share Posted October 23, 2011 Aspirin (Mr = 180) has the formula C9H8O4. One mole of aspirin reacts in the cold with one mole of sodium hydroxide. A tablet of a commercial painkiller has a mass of 0.483 g and is known to contain aspirin. It was found that the tablet reacted with exactly 16.65 cm^3 of 0.100 mol dm^-3 NaOH. Calculate the percentage by mass of aspirin in the tablet. I'm lost! What I need to do first? Please, help! Reply Link to post Share on other sites More sharing options...
Peanut Butter Jelly Posted October 23, 2011 Report Share Posted October 23, 2011 Aspirin (Mr = 180) has the formula C9H8O4. One mole of aspirin reacts in the cold with one mole of sodium hydroxide. A tablet of a commercial painkiller has a mass of 0.483 g and is known to contain aspirin. It was found that the tablet reacted with exactly 16.65 cm^3 of 0.100 mol dm^-3 NaOH. Calculate the percentage by mass of aspirin in the tablet. I'm lost! What I need to do first? Please, help!16.65 cm3 = 16.65 mLmol of NaOH = 0.01655L(0.1)=0.001655 moltherefore that means also 0.001655 mol of asprin reactedmol of reacted asprin = 0.001655 mol (180g)=0.2979gmass by percentage =0.2979/0.483=62% 1 Reply Link to post Share on other sites More sharing options...
Drake Glau Posted October 24, 2011 Report Share Posted October 24, 2011 Aspirin (Mr = 180) has the formula C9H8O4. One mole of aspirin reacts in the cold with one mole of sodium hydroxide. A tablet of a commercial painkiller has a mass of 0.483 g and is known to contain aspirin. It was found that the tablet reacted with exactly 16.65 cm^3 of 0.100 mol dm^-3 NaOH. Calculate the percentage by mass of aspirin in the tablet. I'm lost! What I need to do first? Please, help! 16.65 cm3 = 16.65 mL mol of NaOH = 0.01655L(0.1) =0.001655 mol therefore that means also 0.001655 mol of asprin reacted mol of reacted asprin = 0.001655 mol (180g) =0.2979g mass by percentage =0.2979/0.483 =62% This is how you do it except you changed your volume when you converted it to liters. 16.65mL=0.01665L not 0.01655 Still the same % when rounded though Reply Link to post Share on other sites More sharing options...
Drake Glau Posted November 6, 2011 Report Share Posted November 6, 2011 ICE chartN2 + 3H2 <=> 2NH3-x.......-3x..........+2x2x=0.060x=0.030[H2]equil=0.2-3(0.030)=0.11[N2]equil=0.2-0.030=0.17[NH3]equil=0.060Kc=[NH3]2/([N2][H2]3)=0.0602/(0.17*0.113)=0.060/0.00022627=265.17So this means the reaction MAJORLY prefers the products which if I remember right that Haber process was like this but I'm not entirely sure.It was either the ice chart or using the ideal gas law PV=nRT because using this you can get n/V=P/RT which is the same as concentration=P/RT but you didn't seem to have a temperature to use... 1 Reply Link to post Share on other sites More sharing options...
GeorgieC Posted November 6, 2011 Report Share Posted November 6, 2011 I'm doing Option D Medicines and Drugs SL and I'm wondering if anyone can tell me if I need to know about chirality and the chiral auxiliary? There is very little about it in the two texts I have and I'm confused because I just got an SL question about chirality. Does anyone know if it's on the syllabus for SL? Reply Link to post Share on other sites More sharing options...
Drake Glau Posted November 6, 2011 Report Share Posted November 6, 2011 I'm doing Option D Medicines and Drugs SL and I'm wondering if anyone can tell me if I need to know about chirality and the chiral auxiliary? There is very little about it in the two texts I have and I'm confused because I just got an SL question about chirality. Does anyone know if it's on the syllabus for SL?Last year it was HL only. This year could be a different but I doubt it since you don't learn about chirality in the organic topic until HL also. Reply Link to post Share on other sites More sharing options...
jonathan810 Posted November 6, 2011 Report Share Posted November 6, 2011 Can anyone help me with part b)? The answer says the gradient = -Ea/R which results in -30000K- how do they get it, (the -30000K) Cheers Reply Link to post Share on other sites More sharing options...
timtamboy63 Posted November 6, 2011 Report Share Posted November 6, 2011 (edited) Can anyone help me with part b)? The answer says the gradient = -Ea/R which results in -30000K- how do they get it, (the -30000K) Cheers Enjoy: In the exam, obviously don't write all your reasoning, it's a waste of time, I just did it so you could see how i got there Edited November 6, 2011 by timtamboy63 3 Reply Link to post Share on other sites More sharing options...
helpme123 Posted November 6, 2011 Report Share Posted November 6, 2011 Stuck on yet again another eqm question2NO2 (g) <=> N2O4 (g) Kc = 1 at 328KTwo moles of 2NO2 (g) and two moles of N2O4 (g) were placed in an empty 1 dm3 container and allowed to come to equilibrium at 328K. Predict, with reference to the value of Kc, whether the equilibrium mixture would contain more or less than two moles of 2NO2 (g). Reply Link to post Share on other sites More sharing options...
CkyBlue Posted November 6, 2011 Report Share Posted November 6, 2011 I am plotting a concentration/time graph, which looks like logistic function flipped horizontally. (kind of like Z, but a function) This is a decomposition reaction...meaning the concentration is smaller as the time passesHow do I find the maximum rate of reaction, and the time at which it occurs? And how do I make my tangent line at the point of the maximum rate? I've been told that the slope is the rate of reaction, but the points are REALLY flat in the beginning...And isn't the rate of reaction faster when concentration greater? Reply Link to post Share on other sites More sharing options...
Drake Glau Posted November 7, 2011 Report Share Posted November 7, 2011 Stuck on yet again another eqm question 2NO2 (g) <=> N2O4 (g) Kc = 1 at 328K Two moles of 2NO2 (g) and two moles of N2O4 (g) were placed in an empty 1 dm3 container and allowed to come to equilibrium at 328K. Predict, with reference to the value of Kc, whether the equilibrium mixture would contain more or less than two moles of 2NO2 (g). Kc=[N2O2]/[NO2]2=1 at 328K This tells us that [N2O2]=[NO2]2 Now we know that [NO2]>[N2O2] So it should be less than 2 moles I am plotting a concentration/time graph, which looks like logistic function flipped horizontally. (kind of like Z, but a function) This is a decomposition reaction...meaning the concentration is smaller as the time passes How do I find the maximum rate of reaction, and the time at which it occurs? And how do I make my tangent line at the point of the maximum rate? I've been told that the slope is the rate of reaction, but the points are REALLY flat in the beginning... And isn't the rate of reaction faster when concentration greater? Reactions go faster with the highest concentration when something is reacting with something. A decomp reaction would just occur with something reacting with it since I'm assuming whatever you used was a spontaneous decomposition since most of them are. The reasoning for the faster rate with higher concentrations is because of collision theory but in decomp's case there really isn't anything colliding to react. I'm interpreting what you are saying about your graph as the plateau of the graph is at the beginning right? Anyway, I'd say that the last point on your graph would have the highest rate. I have this explanation in my head but I really can't explain it to you What reaction is it? It matters if there is a gas or solid being formed because that would affect the volume and also affect your concentrations and it would help me explain this 1 Reply Link to post Share on other sites More sharing options...
mackdaddy Posted November 18, 2011 Report Share Posted November 18, 2011 I'm reviewing acids and bases and have the following question:Calculate the pH of a mixture of 50.0 cm3 of 0.100 mol dm–3 aqueous ammonia and 50.0 cm3 of 0.0500 mol dm–3 ammonium chloride solution.Any help would be appreciated!I have the following review question:The equilibrium reached when ethanoic acid is added to water can be represented by the following equation: CH3COOH(l) + H2O(l) < ---- >CH3COO–(aq)+H3O+(aq)Define the terms Brønsted-Lowry acid and Lewis base, and identify two examples of each of these species in the equation.Thanks!! Reply Link to post Share on other sites More sharing options...
dessskris Posted November 18, 2011 Report Share Posted November 18, 2011 find the number of mol of each compund. find the total number of mol of H+ ions. sum the volume of both substances and find the concentration of H+.pH=-log(concentration of H+) Reply Link to post Share on other sites More sharing options...
mackdaddy Posted November 18, 2011 Report Share Posted November 18, 2011 Came across this review question and need help as well as explanation!When the following 1.0 mol dm–3 aqueous solutions are arranged in order of increasing pH, which is the correct order? I. Ammonium chlorideII. Ammonium ethanoateIII. Sodium ethanoatePlease and thank you! Reply Link to post Share on other sites More sharing options...
Drake Glau Posted November 19, 2011 Report Share Posted November 19, 2011 I. is a weak base/strong acid salt. II. is a weak based/weak acid salt III. is a strong base/weak acid salt Increasing pH should be already in order I think....I II III Determining the pH of conjugates never did well for me though sooooo...good luck? 1 Reply Link to post Share on other sites More sharing options...
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