When 0.875 g. of magnesium was heated in air, 1.25 g. of magnesium oxide (MgO) was produced. How much oxygen must be added?

1. What is the coefficient for calcium in the balanced equation?

2 Ca + 5 NaOH → 4 Na + 2 Ca(OH)2

2. The burning of 20.0 g of acetylene (C2H2) produces what mass of carbon dioxide? You must

write the equation, balance it and solve the mass-mass problem.

a. Balanced equation:

2 C2H2 + 5 O2  4 CO2 + 2 H2O

Explanation:

in the given question, the partial pressure is calculated by using the ideal gas equation, that is, pv = nrt

here, p is pressure, v is volume = 25 l, n is number of moles = 0.0104 moles, r is gas constant = -0.0821 l.atm / mol.k

t is temperature = 273 k

p = nrt / v

p = (0.0104 mol × 0.0821 l.atm / mol.k × 273 k) / 25 l

= 0.0093 atm