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Homework Help: Coloumb's Law and Electric Dipoles question

  1. Jan 29, 2015 #1
    1. The problem statement, all variables and given/known data
    1)HCl consists of one H and Cl atom separated by 0.127 nm, the bond length. The Cl atom has a partial charge of -0.177e and the H atom has a partial charge of +0.177e, where e = 1.602x10-19 C is the electron charge.

    2)Now the HCl molecule is placed near a sodium ion Na+ with charge +1e. As shown in the figure, the distance between the Cl and Na atoms is d = 1.6 nm.

    2. Relevant equations
    I had finished question 1, but am stuck on question 2.

    3. The attempt at a solution
    I started with k(q1)(q2)/r^2 ----> (9x10^9) x (2.83554e-20) x (1.602e-19) / (1.727e-9)^2

    I end up with an answer with 1.37e-11, but it is saying it is wrong. What am i doing incorrectly?
  2. jcsd
  3. Jan 29, 2015 #2


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    Staff: Mentor

    What are the questions associated with 1) and 2). What are you supposed to calculate?

    The diagram referenced would be helpful: What are the relative positions of the charges? Is the Na ion on the axis of the dipole formed by the H and Cl atoms?

    Note that fields and forces are vector quantities: they have both magnitude and direction. They also have units associated with them. Don't forget to include units on all results!
  4. Jan 29, 2015 #3
    Ah im sorry. The question I am supposed to answer is :

    What is the magnitude of the total force on the HCl molecule due to the Na+ ion |FHCl|?
  5. Jan 29, 2015 #4


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    Staff: Mentor

    You should make a sketch of the arrangement and draw in the force vectors operating on the H and Cl atoms due to the Na atom. Also indicate their X and Y components. Can you tell what the sum of those vectors will be from the sketch?
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