Quantitative Chemistry: Conservation of Mass (DONE) Flashcards
What is the law of conservation of mass? (2)
The law of conservation of mass states that in a chemical reaction no atoms are lost or made during a chemical reaction, so the mass of the products equals the mass of the reactants.
For example, the carbon atom in coal becomes carbon dioxide when it is burned. The carbon atom changes from a solid structure to a gas but its mass does not change.
What is the law of conservation of mass used to work out?
The law of conservation of mass is used to work out the masses of chemicals in a reaction.
if 24g of Mg reacted with 71g of Cl. Calculate the mass of magnesium chloride produced
Remember the law of conservation of mass states that no atoms are lost or made in a chemical reaction. So the mass of the products equals the mass of the reactants.
Mg (24g) + Cl2 (71g) → MgCl2
(reactants) (products)
In this reaction, the mass of the reactants is 24g + 71g which is 95g. So that means that the mass of the product must also be 95g. The mass of magnesium chloride produced is 95g.
92g of sodium reacted with 32g of oxygen. Calculate the mass of sodium oxide produced.
124g of sodium oxide is produced.
A mass of calcium carbonate reacted to produce 112g of calcium oxide and 88g of carbon dioxide. Calculate the mass of calcium carbonate that reacted.
We know that 200g of calcium carbonate must have reacted because the products have a combined mass of 200g and we know that no atoms can be gained or lost during a chemical reaction so the mass had to stay the same.
112 + 88 = 200
calcium carbonate (reactants) → calcium oxide (112g) + carbon dioxide (88g) (products)
A mass of magnesium oxide reacts with 73g of hydrogen chloride to produce 95g of magnesium chloride and 18g of water. Calculate the mass of magnesium oxide in the reaction.
magnesium oxide + hydrogen chloride (73g) → magnesium chloride (95g) + water (18g)
The total mass of product is 113g. We started with 73g of hydrogen chloride and we’ve got to calculate the mass of magnesium oxide that reacted. The total mass of the reactants has to be the same as the total mass of product. This means that the mass of the magnesium oxide must be 113g - 73g which is 40g.
