An aqueous solution was prepared by dissolving 10.93 g of KBr in enough water to

Question

An aqueous solution was prepared by dissolving 10.93 g of KBr in enough water to make 750.0 ml of solution. What is the molarity of KBr in the solution? (molar mass of KBr: 119.00 g/mol) a) Astatine, having atomic number 85 on the periodic table, is a radioactive member of the halogens. Give the full electron configuration of At. b) Give the electron configurations of the following ions. Fe^2+ Ca^2+ Cl^- c) What are quantum numbers? Give all the possible quantum numbers that an electron in the n = 2 level can have. d) What is meant energy is quantized? How does that give rise to the emission spectra of an element?

Explanation / Answer

1)

mass of KBr = 10.93 g

moles of KBr = 10.93 / 119 = 0.09185 mol

volume = 750 mL = 0.750 L

Molarity = moles / volume

              = 0.09185 / 0.750

Molarity = 0.1225 M

2)

a)

electron configuration of At = [Xe] 4f14 5d10 6s2 6p5

full electron configuration of At = 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f14 5d10 6s2 6p5

b)

Fe+2 = 1s2 2s2 2p6 3s2 3p6 3d10 4p6

Ca+2 = 1s2 2s2 2p6 3s2 3p6

Cl- = 1s2 2s2 2p6 3s2 3p6

c)

n = 2 . l = 1 , m = 3 , (-1 . 0 , +1)

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