Law of Conservation of Mass

Lesson 9: Law of Conservation of Mass

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Applying the Law of Conservation of Mass

Example 1:

Some potassium oxide was placed in 9 grams of water and 112 grams of potassium hydroxide were made. What mass of potassium oxide was used?

Write the word equation	potassium oxide + water potassium hydroxide
Place the masses of the given substance below the equation	?	9 g	112 g
Apply the law of conservation of mass	? + 9 = 112
Solve for the missing mass	? = 112 - 9 ? = 103 So 103 grams of potassium oxide were added to the water.

Example 2:

When 245 grams of potassium chlorate are heated, the potassium chlorate breaks down into 78 grams of potassium, 71 grams of chlorine and some oxygen gas. Find out the mass of oxygen gas formed?

Write a word equation	potassium chlorate + heat potassium + chlorine + oxygen
Place the masses of the given substances below the equation	245 g	78 g	71 g	?
Apply the law of conservation of mass	245 = 78 + 71 + ?
Solve	245 = 149 + ? ? = 245 - 149 ? = 96 So 96 grams of oxygen gas was formed.