confusion

  1. B

    Dilutions confusion - please help

    Hi there, I am a biology undergrad with some highschoool chem problems based on dilutions - please help! If I have a solution of 2.5% solution does this mean 2.5g per 100ml? Assuming yes, that gives me 0.025g per 1ml and therefore 25mg per 1ml. The question is what volume do I need to have...
  2. M

    help me with a confusion

    sequence of Melting point(M.p.) of- Na2O MgO Al2O3 sequence of Melting point of- KCl CaCl2 AlCl3 SnCl4 in some books it is decreasing in order -covalent character increases M.P decreases somewhere it is increasing in order -lattice energy( which is directly propotional to charge&inversaly...
  3. E

    Mole calculations confusion (please help!)

    Hello guys! Im really confused with this one part of calculating the number of moles in 1.00 gram the last part in bold is confusing me. why is the 2 negative? can someone please explain finding a number of moles in a certain number of grams? im really confused : ( this is what the teacher...
  4. M

    Confusion with significant figures...

    I know all of my rules, however am struggling with these two questions: Considering carefully whether the number given is exact or not, how many significant figures in the number in the following statement? There are 50 pencils. Considering carefully whether the number given is exact or not...
  5. D

    Concentrations confusion

    Hi, I am meant to be following a GAG purification protocol from a paper but I dont understand how to make 2 solutions. The paper says "and trichloroacetic acid was added to a final concentration of 5%." Then it says "Three volumes of 5% potassium acetate in ethanol". I don't understand how...
  6. S

    Confusion about Mass, Sig-figs, & Rounding

    I am having trouble with this because the value I calculate is different than the given answer. mass(m) = Number of moles(n) * molar mass(M) Molar masses calculated using the periodic table will have two decimal places for consistency. Determine the mass 2.10 mol of sodium phosphate cleaner...
  7. Z

    Confusion with buffers

    Hey guys. I have been going through the problems set by my professor but some of the methods given in the booklet do not make sense. Problem 1 (I did solve this one). HAc and NaAc is a buffer sol. [HAc]=[NaAc]=0.001M HAc + H20 ⇌ H3O+ + Ac- Ka=1.73*10^-5 Ka=([H+]*[Ac-])/[HAc] Suppose f mol...