Question

1. From the data below, calculate the moles of magnesium used:

Linear density of Mg ribbon: 1.084 g/m (given in lab)

Length used: 6.18 cm

2. From the data below, calculate the moles of hydrogen gas produced:

Volume gas collected: 70.4 mL

Temperature of gas: 21.4 ºC

Barometric pressure: 74.77 cm Hg

Vapor pressure of water at 21.4 ºC : 19.231 mmHg

Hint: Use the ideal gas law equation and be sure to convert to the proper units!

Answer 1

1. linear density= 1.084 g/m

length used= 6.18 cm

so, mass of magnesium= 1.084 g/m * 6.18 cm * 1m/100cm => 0.07 g

then moles=> mass/Molecular weight= 0.07 g/ 24 g/mol=> 0.003 moles

2. Volume=> 70.4 ml=> 70.4/1000 litre=> 0.07 L

Temperature=> 21.4°C => 21.4+273=> 294.4 K

Pressure=> 74.77 cm Hg => 74.77 cm Hg * 1atm/ 76 cm Hg=> 0.98 atm

Applying ideal gas law equation,

PV = nRT

where P is pressure

V is volume of gas

n is number of moles of gas

R is gas constant 0.0821 l atm/mol K

T is temperature.

0.98 atm * 0.07 L = n * 0.0821 L atm / mol K * 294.4 K

=> n = 0.003 moles