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natulia [17]
2 years ago
8

Question 14 A student dissolves 1.5g of styrene C8H8 in 225.mL of a solvent with a density of 1.02/gmL . The student notices tha

t the volume of the solvent does not change when the styrene dissolves in it. Calculate the molarity and molality of the student's solution. Round both of your answers to 2 significant digits. molarity = molality = Ă—10
Chemistry
2 answers:
Yuki888 [10]2 years ago
8 0

We must to know:

Cm = molarity = niu / Vs, when the niu = no. of moles and Vs = Volume of solution

the no. niu = mass / molecular mass of substance

molecular mass of C8H8 = 12x8+8x1 = 104 g/mol

=> niu = 1,5 / 104 = 0,0144 moles C8H8

=> Cm = 0,0144/0,225 = 0,06 mol/L

Cmm = molality = niu (C8H8) / mass of solvent (kg)

=> p = mass / V => mass (solvent) = p x V

=> 225 x 1,02 = 229,5 g solvent = 0,2295 kg solvent

=> Cmm = 0,0144 / 0,229,5 = 0,063

Nata [24]2 years ago
6 0

Answers:

a. 0.064 mol/L; b. 0.063 mol/kg

Explanation:

a. Molar concentration

c = moles/litres

=====

Moles = 1.5 × 1/104.15

Moles = 0.0144 mol

=====

Litres = 225. × 1/1000

Litres = 0.225. L

=====

c = 0.0144/0.225.

c = 0.064 mol·L⁻¹

===============

b. Molal concentration

b = moles of solute/kilograms of solvent

=====

Mass of solvent = 225. × 1.02/1

Mass of solvent = 229.5 g      Convert to kilograms

Mass of solvent = 0.2295 kg

=====

b = 0.0144/0.2295

b = 0.063 mol/kg

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