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Lesson: Conservation of Mass

In this lesson, we will learn how to apply the law of conservation of mass to deduce the masses of reactants and products in a chemical reaction.

Worksheet • 16 Questions

Q1:

Yeast converts glucose to ethanol and carbon dioxide by anaerobic fermentation, as represented by the equation: In a particular fermentation process, 200.0 g of glucose is fully converted.

What is the total mass of ethanol and carbon dioxide at the end of the reaction?

If the fermentation process were carried out in an open container, would the mass of the container increase, decrease or stay the same?

  • AIncrease
  • BDecrease
  • CStay the same

If the reaction produces 97.7 g of carbon dioxide, what mass of ethanol is produced?

Q2:

To 3 significant figures, how much water can be produced from 4.800 g of oxygen and 0.5846 g of hydrogen?

Q3:

When aqueous solutions of sodium hydroxide and magnesium chloride are mixed, magnesium hydroxide precipitates. Calculate the mass of sodium hydroxide required to produce 16.0 g of magnesium hydroxide.

Q4:

Calculate the mass of gallium(III) oxide ( G a O ) 2 3 that can be prepared from 29.0 g of gallium.

Q5:

Calculate the mass of oxygen reacted in the complete combustion of 702 g of octane.

Q6:

The reaction of calcium hydroxide with phosphoric acid ( H P O ) 3 4 produces calcium phosphate and water as the only products. Calculate the mass of calcium hydroxide needed for 113 g of phosphoric acid to completely react.

Q7:

Iron(III) oxide and carbon monoxide react to form metallic iron and carbon dioxide as the only products.

Write a balanced chemical equation for this reaction, including state symbols.

  • A F e O ( ) + 3 C O ( ) 2 F e ( ) + 3 C O ( ) 2 3 2 s g s g
  • B F e O ( ) + 2 C O ( ) F e ( ) + 2 C O ( ) 2 2 s g s g
  • C F e O ( ) + C O ( ) 2 F e ( ) + C O ( ) s g s g 2
  • D F e O ( ) + 2 C O ( ) 3 F e ( ) + 2 C O ( ) 3 2 2 s g s g
  • E F e O ( ) + 3 C O ( ) F e ( ) + 3 C O ( ) 3 2 s g s g

Calculate the mass of carbon monoxide needed for 25.13 g of iron(III) oxide to completely react, to three significant figures.

Calculate the mass of iron produced if 12.99 g of iron(III) oxide reacts with 6.750 g of carbon monoxide, to three significant figures.

Q8:

Aluminum and iodine react to form aluminum iodide as the only product.

Write a balanced chemical equation for this reaction, including state symbols.

  • A 2 A l ( ) + 3 I ( ) 2 A l I ( ) s s s 2 3
  • B 4 A l ( ) + 3 I ( ) 2 A l I ( ) s s s 2 2 3
  • C A l ( ) + I ( ) A l I ( ) s s s 2 2
  • D 2 A l ( ) + I ( ) 2 A l I ( ) s s s 2
  • E A l ( ) + 2 I ( ) A l I ( ) s s s 2 4

Calculate the number of moles of iodine needed for 0.429 mol of aluminum to completely react.

Calculate the mass of aluminum iodide produced if 3.50 g of iodine reacts with 0.350 g of aluminum.

Q9:

Silicon and nitrogen gas react to form silicon nitride as the only product.

Write a balanced chemical equation for this reaction, including state symbols.

  • A 3 S i ( ) + 2 N ( ) S i N ( ) s g s 2 3 4
  • B 4 S i ( ) + 3 N ( ) 2 S i N ( ) s g s 2 2 3
  • C S i ( ) + 2 N ( ) S i N ( ) s g s 2 4
  • D 3 S i ( ) + N ( ) S i N ( ) s g s 2 3 2
  • E S i ( ) + N ( ) S i N ( ) s g s 2 2

Calculate the mass of nitrogen needed for 8.080 g of silicon to completely react, to three significant figures.

Calculate the mass of silicon nitride produced if 53.20 g of silicon reacts with 36.37 g of nitrogen, to three significant figures.

Q10:

Antoine Lavoisier was one of the first scientists to state the law of conservation of mass. When he heated a sample of tin and air in an air-tight flask, tin reacted with oxygen in the air to produce tin oxide. Did the mass of the flask and its contents increase, decrease or stay the same because of this reaction?

  • AIncreased
  • BStayed the same
  • CDecreased

Q11:

Bread dough is placed in a baking tin and baked at 1 8 0 ∘ C . What happens to the mass of the bread?

  • AIt increases
  • BIt decreases
  • CIt stays the same

Q12:

A piece of magnesium ribbon is burned in air, producing white powdered magnesium oxide. Is the mass of the oxide greater than, less than or equal to that of the magnesium ribbon it came from?

  • ALess than
  • BGreater than
  • CEqual to

Q13:

Why do we use an object’s mass, rather than its weight, to indicate the amount of matter it contains?

  • AWeight depends on gravity, which depends on where you are in the universe. Mass is universal.
  • BThe numbers we get for mass are smaller and easier to handle.
  • CMass is more accurate than weight.
  • DMass depends on gravity, which is fixed.
  • EActually, we should use weight but mass is easier to measure.

Q14:

A wet 43.2 g sample of copper sulfate heptahydrate ( C u S O · 7 H O ) 4 2 is heated until only copper sulfate ( C u S O ) 4 remains. The mass of the water lost is 34.1 g. What is the mass of the copper sulfate?

Q15:

A 13.5 g sample of calcium carbonate is heated until it decomposes completely and 7.6 g of calcium oxide is produced. What is the mass of carbon dioxide produced?

Q16:

Magnesium burns in air to produce magnesium oxide. If a sample of magnesium requires 15.0 g of oxygen to burn completely and forms 37.8 g of magnesium oxide, what is the mass of the sample of magnesium?
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