Answer:
Step-by-step 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