Chemistry, 29.07.2019 11:00 keigleyhannah30

A0.465 g sample of an unknown compound occupies 245 ml at 298 k and 1.22 atm. what is the molar mass of the unknown compound? a.26.3 g/mol b.33.9 g/mol c.12.2 g/mol d.38.0 g/mol e.81.8 g/mol

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we can find the number of moles of gas using the ideal gas law equation

PV = nRT

where P - pressure - 1.22 atm

V - volume - 0.245 L

n - number of moles

R - gas constant - 0.08206 L.atm/mol.K

T - temperature - 298 K

substituting the values in the equation

1.22 atm x 0.245 L = n x 0.08206 L.atm/mol.K x 298 K

n = 0.0122 mol

molar mass of compound = mass present / number of moles therefore molar mass = 0.465 g / 0.0122 mol = 38.1 g/mol
the answer is d) 38.0 g/mol

Answer from: Quest

when 25.0 ml of 0.700 mol/l naoh was mixed in a calorimeter with 25.0 ml of 0.700 mol/l hcl, both initially at 20.0 °c, the temperature increased to 22.1 °c. the heat capacity of the calorimeter is 279 j/°c.

the equation for the reaction is:

naoh + hcl → nacl + h₂o

moles of hcl = 0.0250 l hcl ×

0.700

mol hcl

1 l hcl = 0.0175 mol hcl

volume of solution = (25.0 + 25.0) ml = 50.0 ml

mass of solution = 50.0 ml soln ×

1.00

ml soln

= 50.0 g soln

δt=t2-t1

= (22.1 – 20.0) °c = 2.1 °c

the heats involved are

heat from neutralization + heat to warm solution + heat to warm calorimeter = 0

q1+q2+q3=0

nδh+mcδt+cδt=0

0.0175 mol ×

δh

+ 50.0 g × 4.184 j·g⁻¹°c⁻¹ × 2.1 °c + 279 j°c⁻¹ × 2.1 °c = 0

0.0175 mol ×

δh

+ 439.32 j + 585.9 j = 0

0.0175 mol ×

δh

= -1025.22 j

δh=1025.22j0.0175 mol= -58 600 j/mol = -58.6 kj/mol

Answer from: Quest

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A0.465 g sample of an unknown compound occupies 245 ml at 298 k and 1.22 atm. what is the molar mass...

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