here are clearer pictures of those two questions Due in class on Tuesday, Octobe

Question

here are clearer pictures of those two questions

Due in class on Tuesday, October 17, 2017 1. (4 points) Vitamin B12.cyanocobalamin, contains the element cobalt (Co); each molecule of B12 contains one Co atom. A sample of B12 was found to contain 4.38% Co. What is the molecular mass of Vitamin B12? 2. (4 points) A 20.0 g sample of HF is dissolved in water to produce 255 mL of solution. What is the molarity of the resulting solution? 2o Molnut 3.(4 points) What mass of Naoll (o) is required to react (Le, the stoichiometrically equivalent amount) completely with 25.0 nal, of 1.25 M H2SO4 (ai)?

Explanation / Answer

Given each molecule contain 1 on Co atom in it

1 mol molecule will have 1 mol Co mass in it

4.38 % Co in 1 mol molecule

molar mass of cobalt = 58.93 g/mol

4.38 % of B12 = 58.93 g/mol

B12 = 58.93g/mol / 0.0438 = 1345.4338 g /mol

Molar mass of B12 = 1345.4338 g /mol

2.

molarity = moles / volume of soultion in litres

moles = mass / molar mass = 20g / 20g/mol = 1 mol

volume = 255 mL = 0.255 L

molarity = 1 mol / 0.255 L = 3.92 M

3.

2NaOH + H2SO4 ---->Na2SO4 + 2H2O

1 mol H2SO4 needs 2 mol NaOH

moles of H2SO4 = molarity x volume = 1.25 M x 0.025L = 0.03125 M

moles of NaOH needed = 2 x 0.03125 = 0.0625 moles

molar mass of NaOH = 39.997 g/mol

mass of NaOH = 39.997 g/mol x 0.0625 mol = 2.5 g NaOH needed

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