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General Chemistry 1
Lesson 5 : ATOMS, MOLECULES, AND IONS
Study Materials – August 2018
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Laws of chemical changes
These laws were inferred from several experiments conducted during the 18th
century using a balance for the measurements:
a. Law of Conservation of Mass
b. Law of Definite Proportion
c. Law of Multiple Proportion
Law of Conservation of Mass
In a chemical reaction, no change in mass takes place. The total mass of the
products is equal to the total mass of the reactant. Antoine Lavoisier, a brilliant
French chemist, formulated this law by describing one of his experiments
involving mercuric oxide. He placed a small amount of mercuric oxide, a red solid,
inside a retort and sealed the vessel tightly. He weighed the system, and then
subjected it to high temperature. During the heating, the red solid turned into a
silvery liquid. This observation indicated that a chemical reaction took place. After
which, the setup was cooled and then weighed. The weight of the system was
found to be the same as before heating.
Application
Problem 1: How many grams of water will be formed if 1.00 g hydrogen gas reacts
with 8.00 g oxygen? The reaction can be represented by the following word
equation:
hydrogen + oxygen → water
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Solution:
1.00 g hydrogen + 8.00 g oxygen → ?
1.00 g hydrogen + 8.00 g oxygen → 9.00 g water
ANSWER: 9.00 g water
Problem 2: 5.58 g iron reacted with 3.21 g sulfur. How many grams of iron (II)
sulfide were produced? The reaction involved was:
iron + sulfur → iron (II) sulfide
Solution:
5.58 g iron + 3.21 g sulfur → ?
5.58 g iron + 3.21 g sulfur → 8.79 g iron (II) sulfide
ANSWER: 8.79 g iron (II) sulfide
Problem 3: Magnesium burns in air to form magnesium oxide, as represented by
the following word equation:
magnesium + oxygen → magnesium oxide
When 2.43 g magnesium was burned, 4.03 g magnesium oxide was produced.
How many grams of oxygen reacted with the magnesium?
Solution:
magnesium + oxygen → magnesium oxide
2.43 g magnesium + ? → 4.03 g magnesium oxide
4.03 g magnesium oxide – 2.43g magnesium → ?
4.03 g magnesium oxide – 2.43g magnesium → 1.60 g oxygen
ANSWER: 1.60 g oxygen
General Chemistry 1
Lesson 5 : ATOMS, MOLECULES, AND IONS
Study Materials – August 2018
___________________________________________________________________
Laws of chemical changes
These laws were inferred from several experiments conducted during the 18th
century using a balance for the measurements:
a. Law of Conservation of Mass
b. Law of Definite Proportion
c. Law of Multiple Proportion
Law of Conservation of Mass
In a chemical reaction, no change in mass takes place. The total mass of the
products is equal to the total mass of the reactant. Antoine Lavoisier, a brilliant
French chemist, formulated this law by describing one of his experiments
involving mercuric oxide. He placed a small amount of mercuric oxide, a red solid,
inside a retort and sealed the vessel tightly. He weighed the system, and then
subjected it to high temperature. During the heating, the red solid turned into a
silvery liquid. This observation indicated that a chemical reaction took place. After
which, the setup was cooled and then weighed. The weight of the system was
found to be the same as before heating.
Application
Problem 1: How many grams of water will be formed if 1.00 g hydrogen gas reacts
with 8.00 g oxygen? The reaction can be represented by the following word
equation:
hydrogen + oxygen → water
, Page 2 of 15
Solution:
1.00 g hydrogen + 8.00 g oxygen → ?
1.00 g hydrogen + 8.00 g oxygen → 9.00 g water
ANSWER: 9.00 g water
Problem 2: 5.58 g iron reacted with 3.21 g sulfur. How many grams of iron (II)
sulfide were produced? The reaction involved was:
iron + sulfur → iron (II) sulfide
Solution:
5.58 g iron + 3.21 g sulfur → ?
5.58 g iron + 3.21 g sulfur → 8.79 g iron (II) sulfide
ANSWER: 8.79 g iron (II) sulfide
Problem 3: Magnesium burns in air to form magnesium oxide, as represented by
the following word equation:
magnesium + oxygen → magnesium oxide
When 2.43 g magnesium was burned, 4.03 g magnesium oxide was produced.
How many grams of oxygen reacted with the magnesium?
Solution:
magnesium + oxygen → magnesium oxide
2.43 g magnesium + ? → 4.03 g magnesium oxide
4.03 g magnesium oxide – 2.43g magnesium → ?
4.03 g magnesium oxide – 2.43g magnesium → 1.60 g oxygen
ANSWER: 1.60 g oxygen
