1. How many atoms are there in 2 q of oxygen? 2. Analysis of a mineral compound

Question

1. How many atoms are there in 2 q of oxygen? 2. Analysis of a mineral compound shows it to contain the follow- ing: 38.8 wt. % calcium, 20 wt. % Phosphorus and the rest oxygen. Estinate the compound's simplest chemical formula. 3. A hydrogen atom exists with its electron in the n = 5-state. The electron undergoes a transition to the n= 1 state. Calculate (a) the energy of the photon emitted,' (b) its frequency and (c) ts wavelength in nanometers. 4. Calculate the net potential energy for a Na*cl- ion pair. Use ionic radii found on back of front cover. Assume 9.

Explanation / Answer

1)

mass of oxygen = 2 g

moles of Oxygen = 2 / 16 = 0.125

1 mol -------------> 6.023 x 10^23

0.125 mol   -------------> ??

moles of oxygen atoms = 0.125 x 6.023 x 10^23

                                     = 7.53 x 10^22 atoms

2)

mass % of Ca = 38.8 %

moles of Ca = 38.8 / 40 = 0.97

moles of P = 20 / 31 = 0.645

mass % of O = 41.2 %

moles of O = 2.575

   Ca          P          O

0.97       0.645    2.575

3/2            1          4

   3              2          8

simplest formula = Ca3P2O8

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