Chemistry 11 : Law of Definite Proportions

-   Law of definite proportions – The elements in a compound are always in the same proportion by mass ⇒  The mass percentage of each element in a compound is always the same, no matter the size of the sample

Example -> Water is composed of 88.8% oxygen and 11.2% hydrogen in all cases -> Different compounds can contain the same elements -> H2O, H2O2 -> CH4, C6H6, C2H2

But these compounds will have different percentage compositions Percentage compositions can help identify a compound Some compounds can have the same percentage composition if they ratios between the elements is the same Examples ⇒  C2H2, C6H6 92.27% C, 7.8% H Calculating percentage compositions ⇒  Given the mass of each element ⇒  Calculate the mass percent of each element in the compound ⇒  A compound with  a mass of 4.87g is composed of 3.27g of zinc and 1.60g of sulfur. What is the percentage composition of the compound.