Question

A neon sign is made of glass tubing whose inside diameter is 2.5 cm and whose length is 5.5 m.

[10.36] If the sign contains neon at a pressure of 1.75 torr at 35 ∘C, how many grams of neon are in the sign? (The volume of a cylinder is πr2h.)

Express your answer using two significant figures.

Answer 1

r = 2.5 cm / 2

= 1.25 cm

= 1.25*10^-2 m

h = 5.5 m

so,

volume = pi*r^2*h

= 3.14 * (1.25*10^-2)^2 * 5.5

= 2.70*10^-3 m^3

Given:

P = 1.75 torr

= (1.75/760) atm

= 0.0023 atm

V = 0.0027 m^3

= (0.0027*1000) L

= 2.7 L

T = 35.0 oC

= (35.0+273) K

= 308 K

find number of moles using:

P * V = n*R*T

0.0023 atm * 2.7 L = n * 0.08206 atm.L/mol.K * 308 K

n = 2.46*10^-4 mol

Molar mass of Ne = 20.18 g/mol

use:

mass of Ne,

m = number of mol * molar mass

= 2.46*10^-4 mol * 20.18 g/mol

= 4.964*10^-3 g

Answer: 5.0*10^-3 g