Search results

  1. C

    Spectrum of Tandem MS

    Homework Statement There are four scan modes for tandem MS: Product ion, Precursor ion, Neutral loss scan mode and MRM. e.g. In MRM, the result of graph is Intensity versus time, but NOT versus m/z. What does the "time" in the graph refers to? Homework Equations The Attempt at a Solution...
  2. C

    TLC Rf order

    Homework Statement arrange the following eluents in an increasing order of Rf of aspirin ethyl acetate, n-hexane, n-butanol, methanol Homework Equations The Attempt at a Solution my order is n-hexane < n-butanol < ethyl acetate < methanol but the order is wrong. i am thinking: aspirin is...
  3. C

    Rank the acidity

    Homework Statement BCl3, BF3, B(CH3)3, B(CH3O)3 Rank the acidity of these compounds. Homework Equations The Attempt at a Solution I dont know how to determine the acidity of B(CH3O)3 and how the acidity of BF3 and BCl3 is higher than B(CH3)3 because of F and Cl high electronegativity. How...
  4. C

    Recrystallization process

    In the mix solvent of recrystallization, why it is better to add the second solvent dropwise instead of by one-portion? i it to improve the purification? but why?? is it increase the time of contacting the solvent so as to achieve a better dissolution??
  5. C

    Find local maximum value

    Homework Statement y=(8/5)sint + (4/5) cost - (9/5)e^(-t/2) find its local max Homework Equations The Attempt at a Solution i have differentiated it and found out dy/dx, in order to find the local max, i have to find out the value t when dy/dx=0 but i cant solve this equation
  6. C

    Series converge or diverge

    Homework Statement summation n from 1 to inf, 1/ln(n+5) converge or diverge Homework Equations The Attempt at a Solution 1/ln(n+5) > 1/n (from n=2 to inf) and i proved that it diverges by comparison test, am i correct? i am thinking that as my prove is n from 2 to inf not from 1 to inf...
  7. C

    Galvanic cell

    Homework Statement A is an aqueous solution of KCl(aq) with unknown concentration. The following experiment was carried out at 25°C to determine the concentration of Cl- (aq) in A, and the Ksp of AgCl(s) Step 1: A half-cell was made by dipping a silver strip into 100.0 cm3 of A. Step 2: A...
  8. C

    Convergence or divergence

    Homework Statement ∞ ∑ tan(1/k) k=5 show that it is convergent or divergent Homework Equations The Attempt at a Solution i used ratio test, but it's equal to 1, it means no works... i used divergence test, it equals to 0, no work too... so what should i do? i dont know how to use...
  9. C

    Summation series

    Homework Statement ∞ Σ ( x^n/ln(n+5) ) n=1 find the value of x that the above series converges Homework Equations The Attempt at a Solution i cal. it by ratio test and i found that |x|<1 but when i input (-1,1) into my said it's wrong[/B]
  10. C

    Calculate lim n->inf (n^2/n!)

    Homework Statement calculate lim n->inf (n^2/n!) 2. Homework Equations The Attempt at a Solution i just calculated, and i got inf as the ans... n^2/1X2X3...Xn n/1X2X3...X(n-1) 1/[(1X2X3...)/n](1-1/n) when n->inf, it will go to inf am i correct? or there is something wrong?
  11. C

    Acid dissociation constant

    Homework Statement when 10 cm3 of a monoprotic acid C3H6O3, with concentration of 7.2g/dm3, was titrated against against 0.05M NaCl, the equivalence point reached when 15.75cm3 (ph8) of NaOH was used. Calculate the acid dissociation constant Ka for C3H6O3. Homework Equations The Attempt at...
  12. C

    Integration problem

    Homework Statement integrate 1/(1+e^x) dx Homework Equations The Attempt at a Solution firstly i let t=1+e^x and then i come to : integrate 1/(t^2-1) and then i put t=secx . . . but then the final ans is -1/2 ln | 2/e^x +1 | it should be 1 instead of 2, i hv checked for the steps for so...
  13. C

    Find a combination of n and m

    Homework Statement 1007n+1703m=1 when n and m are integers Homework Equations The Attempt at a Solution i hv tried for so many times, but i cant find it the GCD of 1007 and 1703 is 1, so it is possible to find n and m
  14. C

    Find the last digit of 3^101 X 7^202

    Homework Statement find the last digit of 3^101 X 7^202 Homework Equations The Attempt at a Solution i have cal. that the last digit is 7 by...: [147]mod10 X ([3^4]mod10)^25 X ([7^4]mod10)^25 = [7]mod10 X [1]mod10 = [7]mod10 so the last digit is 7 is it correct?
  15. C

    PH in buffer solution

    Ka values of the 1st and 2nd dissociation of phthalic acid (HO2C-C6H4-CO2H) are given below. Estimate the pH value for highest buffer capacity when a buffer is prepared from 1:1 mixture of phthalic acid and sodium hydrogen phthalate (HO2CC6H4- CO2Na) in water? HO2C-C6H4-CO2H <=> H+...
  16. C

    Sliding down the curved/straight slide

    Homework Statement a boy is sliding down a curved slide, another boy with same mass is sliding down a straight slide. if both slides have the same height, which of them will reach the bottom first? Homework Equations The Attempt at a Solution i m thinking if it is related to 1/2 mv^2 = mgh...
  17. C

    Area bounded

    i m thinking of this... area bounded by x=0, y=0, y=x^2, y=4-x^2 and x=2 why the region bounded by the below three cases are the same 1. x=0, y=0, y=x^2, y=4-x^2 2. y=0, y=x^2, y=4-x^2 3. and x=0, y=x^2, y=4-x^2 but after i add x=2 and compute the bounded region, it's different? i am just...
  18. C

    Centripetal force~

    if the centripetal force can be only provided by normal contact force. centripetal velocity is Vs. If V<Vs, then it will lose contact of the road? Or it will lose contact when n=0? Or when n<0? THX