Laws

Law of Conservation of Mass Lavoisier concluded that when a chemical reaction occurs, mass is neither created nor destroyed but only changed. Lavoisier’s conclusion became known as the law of conservation of mass. Law of Conservation of Mass Clip

Law of Conservation of Mass In this law – mass is neither created nor destroyed – it is conserved Basically that means what you start with has to equal what you end with Mass reactants = Mass products

Example Lets say that you have g of mercury (II) oxide. It is placed into a flask and heated until it is converted into liquid mercury and oxygen gas. If I get 9.26 g of liquid mercury, how much oxygen gas was created?

Example First you need to write the reaction in word form –Mercury (II) oxide  mercury + oxygen Now place the amounts under the reaction –Mercury (II) oxide  mercury + oxygen –(10.00 g) = (9.26 g) + x Solve for x –X = 0.74 g of oxygen gas

Try this one… A reaction between sodium hydroxide and hydrogen chloride gas produces sodium chloride and water. A reaction of g of sodium hydroxide with g of hydrogen chloride gives off g of water. What mass of sodium chloride is formed in the reaction? g sodium chloride

Law of Definite Proportions The elements that composed the compounds were always in a certain proportion by mass. This principle is now referred to as the law of definite proportions. Another way to say this is…water is always water is always water…

The mass of the compound is equal to the sum of the masses of the elements that make up the compound. The ratio of the mass of each element to the total mass of the compound is a percentage called the percent by mass. Law of Definite Proportions

Example A compound is analyzed in the lab an found to contain 8.44 g C, 1.3 g H, and g O. What is the % composition of each element in the compound? First we must find the total mass % = Part x 100 Whole

Example C = 8.44 g H = 1.30 g O = g Total = 20.00g Now find the % of each / g X 100 = 42.2% C 6.50% H 51.30% O We find that this compound is sucrose

Another Example Now let’s say that Mr. Romano finds a mystery white powder in the cafeteria. He asks us to analyze the substance and tell him what it is. We find that there is g of C, 32.5 g H, and g O. What is the % composition of the compound?

Another Example C = g H = 32.5 g O = g Total = g / g X 100 = 42.2% C 6.50% H 51.30% O What is the mystery white powder??? SUCROSE

The law of multiple proportions states that when different compounds are formed by a combination of the same elements, different masses of one element combine with the same relative mass of the other element in a ratio of small whole numbers. Ratios compare the relative amounts of any items or substances. Law of Multiple Proportions

The two distinct compounds water (H 2 O) and hydrogen peroxide (H 2 O 2 ) illustrate the law of multiple proportions. Both water & hydrogen peroxide are made up of hydrogen and oxygen, the difference is in their proportions. When we compare the mass of oxygen in hydrogen peroxide to the mass of oxygen in water, we get the ratio 2:1. Law of Multiple Proportions

Dalton’s Atomic Theory Dalton proposed his atomic theory of matter in Although his theory has been modified slightly to accommodate new discoveries, Dalton’s theory was so insightful that it has remained essentially intact up to the present time.

1.All matter is made up of atoms. 2.Atoms are indestructible and cannot be divided into smaller particles. (Atoms are indivisible.) 3.All atoms of one element are exactly alike, but are different from atoms of other elements. Dalton’s Atomic Theory