Mass Ratios & Law of Multiple Proportions Miss Fogg Fall 2015.

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Presentation transcript:

Mass Ratios & Law of Multiple Proportions Miss Fogg Fall 2015

Mass Ratios Atomic mass = mass of an atom measured in amu (atomic mass units) Mass of oxygen =  16.00amu Mass of hydrogen =  1.01amu

Mass ratios Mass of element X : Mass of element Y How to calculate mass ratios: ◦ 1) Find the mass of each element ◦ 2) Divide each elemental mass by the smallest element mass ◦ 3) Express as ratio and round

Example: H 2 O Find the ratio of oxygen to hydrogen in H 2 O ◦ 1) Find the mass of each element O: 16.00amu x 1 atom = 16.00amu H: 1.01amu x 2 atom =2.02amu

Find the ratio O : H ◦ 2) Divide each elemental mass by the smallest element mass O: 16.00amu ÷ 2.02 = 8.0 H: 2.02amu ÷ 2.02 = 1.0 Example: H 2 O

Find the ratio O : H ◦ 3) Express as ratio and round O: 8.0  8 H: 1.0  1 (Law of definite proportions) In H 2 O, oxygen and hydrogen always have a ratio of “16 to 2” or “8 to 1” by mass 8 : 1 Example: H 2 O

Example: KCl KCl always contains one atom of K for every one atom of Cl Find the ratio K : Cl ◦ 1) Find the mass of each element K: 39.10amu x 1 atom = 39.10amu Cl: 35.45amu x 1 atom =35.45amu

Example: KCl Find the ratio K : Cl ◦ 2) Divide each elemental mass by the smallest element mass K: 39.10amu ÷ = Cl: 35.45amu ÷ 35.45= 1.000

Example: KCl Find the ratio K : Cl ◦ 3) Express as ratio and round K:  1.1 Cl:  1 (Law of definite proportions) In KCl, potassium and chlorine always have a ratio of “39.09 to 35.45” or “1.1 to 1” by mass. 1.1 : 1

Law of Multiple Proportions Dalton’s Law (1804): When 2 elements form different compounds, the mass ratio of the elements in one compound is related to the mass ratio in the other by a small whole number

Nitrogen & Oxygen You have more than one molecule made up of the same elements N 2 Onitrous oxide NOnitric oxide NO 2 nitrogen dioxide OO O ON N N N

Nitrogen & Oxygen N 2 Onitrous oxide Mass nitrogen: 14.01amux 2 = 28.02amu Mass oxygen: 16.00amux1= 16.00amu ONN

Nitrogen & Oxygen N 2 Onitrous oxide Mass nitrogen: 28.02amu Mass oxygen: 16.00amu How many grams of N are used every 1g of O? 28.02amu nitrogen= ? 16.00amu oxygen 1g oxygen ONN 1.751g nitrogen

Nitrogen & Oxygen Mass of N for 1g O N 2 Onitrous oxide1.75g NOnitric oxide NO 2 nitrogen dioxide OO O ON N N N

Nitrogen & Oxygen NOnitric oxide Mass nitrogen: 14.01amux 1 = 14.01amu Mass oxygen: 16.00amux1= 16.00amu ON

Nitrogen & Oxygen NOnitric oxide Mass nitrogen: 14.01amu Mass oxygen: 16.00amu How many grams of N are used every 1g of O? 14.01amu nitrogen= ? 16.00amu oxygen 1g oxygen ON g nitrogen

Nitrogen & Oxygen Mass of N for 1g O N 2 Onitrous oxide1.75g NOnitric oxide0.876g NO 2 nitrogen dioxide OO O ON N N N

Nitrogen & Oxygen NO 2 nitrogen dioxide Mass nitrogen: 14.01amux 1 = 14.01amu Mass oxygen: 16.00amux 2= 32.00amu ONO

Nitrogen & Oxygen NO 2 nitrogen dioxide Mass nitrogen: 14.01amu Mass oxygen: 32.00amu How many grams of N are used every 1g of O? 14.01amu nitrogen= ? 32.00amu oxygen 1g oxygen ON g nitrogen O

Nitrogen & Oxygen Mass of N for 1g O N 2 Onitrous oxide1.75g NOnitric oxide0.876g NO 2 nitrogen dioxide0.438g OO O ON N N N How are all these numbers related?

Nitrogen & Oxygen Mass of N for 1g O N 2 Onitrous oxide1.75g NOnitric oxide0.876g NO 2 nitrogen dioxide0.438g OO O ON N N N How are all these numbers related? Law of multiple proportions! 1.75 ÷ = = ÷ = ÷ = = 4

Ch3 Homework - Due tomorrow (10/7): Assessment Problems Page 76: 20-24; 30 Page 83: Problems 60-69; 74-75