How many grams of oxygen gas will react completely with a block of calcium metal that is 3.0 cm by 3.5 cm by 4.2 cm, if the density of calcium is 1.55 g/ml?

Answers:

D) 27 g

Step-by-step explanation:

(1) Calculate the mass of Ca

(a) Calculate the volume of the block

V = lwh

V = 4.2 cm × 3.5 cm × 3.0 cm

V = 44.1 cm³

(b) Calculate the mass of the block·

ρ = m/V   Multiply each side by V

m = Vρ

m = 44.1 cm³ × (1.55 g/1 cm³)

m = 68.4 g

(2) Calculate the mass of oxygen

We know we will need a balanced equation with masses and molar masses, so let’s gather all the information in one place.  

M_r:  40.08  32.00

          2Ca  +   O₂ ⟶ CaO

m/g:  68.4

(a) Calculate the moles of Ca

n = 68.4 g Ca ×1 mol Ca/40.08 g NH₃

n = 1.71 mol Ca

(b) Calculate the moles of O₂

The molar ratio is (1 mol O₂/2 mol Ca)

n = 1.71 mol Ca × (1 mol O₂/2 mol Ca)

n = 0.853 mol O₂

(c) Calculate the mass of O₂

Mass of O₂ = 0.853 mol O₂ × (32.00 g O₂/1 mol O₂)

Mass of O₂ = 27 g O₂

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