Question

Please help me please

Answer 1

Answer:

Explanation:

Molarity = moles / volume (L)

moles = mass (g) / Molecular weight (g/mol)

so you have mass in gram and volume in ml ( Volume must be in litter because unit of mass is gram )

g = L     ,   mg = ml

first you must calculate the number of moles for each molecule and convert the ml to L and use the molarity law to calculate molarity for each molecule .

Ex71.

a.   Mw for NaCl = 23+35 = 58 g/mole

no of moles = 1.5 / 58 = 0.025

ml to L = 100/1000 = 0.1 L

Molarity = 0.025 / 0.1 = 0.25 M

b. Mw for K2CrO4 = 39x2 + 52 + 16x4 = 194 g/mol

no of moles = 1.5 / 194 = 0.0077

ml to L = 100 / 1000 = 0.1 L

Molarity = 0.0077 / 0.1 = 0.077 M

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Ex 72

a.  Mw for MgBr = 24 + 80 = 104 g/mol

no of moles = 20 / 104 = 0.19

ml to L = 250 / 1000 = 0.25 L

Molarity = 0.19 / 0.25 = 0.76 M

b. Mw for LiCO = 7 + 12 + 16 = 35 g/mol

no of moles = 5.55 / 35 = 0.158 moles

ml to L = 75 / 1000 = 0.075 L

Molarity = 0.158 / 0.075 = 2.106 M

Good Luck