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Experiment 2 Conservation of Copper
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 Antoine Lavoisier | Introduction/Background
Antoine Lavoisier (1743-1794), the father of modern chemistry, was the first to observe the law of conservation of mass. This law says that the amount of matter in the universe is constant. This means that atoms can neither be made nor destroyed. Pretty cool, huh? It is because of the law of conservation of mass that we are able to write balanced chemical reactions. This makes it possible to predict the masses of reactants and products involved in a chemical reaction. |
Key Concepts
A fundamental chemical law is the law of conservation of mass (which is also known as the law of conservation of matter). This law states that mass cannot be created or destroyed; or in other words, the total mass of materials present after a chemical reaction will be the same as the total mass before the reaction. Mass is just a measure of the amount of material in an object. The SI unit (the preferred metric units for use in scientific measurements) for mass is the kilogram (kg), which is equal to about 2.2 pounds (lbs). Mass can easily be converted into moles, which is just another unit of amount in chemistry. Since mass can be mathematically converted into mass, the law of conservation of mass can also be referred to as the law of conservation of moles (the total moles on one side of the equation must be equal to the total moles on the other side of the equation). Therefore, this law allows us to balance equations. Let's try balancing the following reactions.
Unbalanced
Balanced |
HCl + Mg(OH)2 → MgCl2 + H2O
2HCl + Mg(OH)2 → MgCl2 + 2H2O
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Unbalanced
Balanced |
C2H6 + O2 → CO2 + H2O
click to reveal |
Now apply the law of conservation of mass to the equation for a chemical reaction.
Example 1: Some potassium oxide (K2O) was placed in 9g of water and 112g of potassium hydroxide (KOH) was made. What mass of potassium oxide reacted?
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| Write the word equation |
Potassium oxide + water → potassium hydroxide |
| Place the masses of the given substance below the equation |
??? + 9g → 112g |
| Apply the law of conservation of mass |
? + 9g = 112g |
| Solve for the missing mass |
112g - 9g = ? ? = 103g |
Answer: 103g of potassium oxide reacted with the water.
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Example 2: When 245 grams of potassium chlorate are heated, the potassium chlorate breaks down into 149g potassium chloride and some oxygen gas. Find out the mass of oxygen gas formed.
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| Write the word equation |
Potassium chlorate → potassium chloride + oxygen |
| Place the masses of the given substance below the equation |
245g → 149g + ??? |
| Apply the law of conservation of mass |
245g = 149g + ? |
| Solve for the missing mass |
245g - 149g = ? ? |
Answer: click to reveal
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Example 3: When 12 grams of NaOH are added to 16 grams of HCl, 7 grams of H2O and some amount of NaCl are formed. Find the mass of NaCl formed.
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| Write the equation |
NaOH + HCl → H2O + NaCl |
| Place the masses of the given substance below the equation |
12g + 16g → 7g + ??? |
| Apply the law of conservation of mass |
12g + 16g = 7g + ? |
| Solve for the missing mass |
28g - 7g = ? |
Answer: click to reveal
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Glossary
Atom = the smallest particle of an element that can exist either alone or in combination.
Mole = the base unit of amount of pure substance in the International System of Units that contains the same number of elementary entities as there are atoms in exactly 12 grams of the isotope carbon 12.
SI Unit = System Internationale Units are units agreed upon by the international community to be used in publications and research documents so that everyone will be able to understand them.
Related Materials
For more help on balancing reaction equations:
Balancing Chemical Equations (http://www.chemistry.ohio-state.edu/betha/nealChemBal/)
For more information about the law of conservation of mass:
Antoine-Laurent Lavoisier (http://www.chemheritage.org/EducationalServices/chemach/fore/all.html)
Antoine Lavoisier (http://www.fact-index.com/a/an/antoine_lavoisier.html)