Chemistry: Calculating Element Percentages in Compounds & Items, Slides of Chemistry

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Percent

Composition

You can find the % composition of

anything

 What % of the students in this class

have their calculators?

 What % of students in this class are

wearing blue shirts?

 The process is always the same

Count how many ÷ the total x 100% =

% composition

% Composition of Chocolate Chip Cookies  Flour 300g  Baking Soda 6g  Salt 6g  Brown Sugar 300g  Butter 230g  Eggs 40g  Vanilla 12g  Chocolate Chips 340g  Total 1234g

You can Find each one Separately Flour 300g ÷ 1234g x100% = 24.31% Baking Soda 6g ÷ 1234g x100% = 0.49% Salt 6g ÷ 1234g x100% = 0.49% Brown Sugar 300g ÷ 1234g x100% = 24.31% Butter 230g ÷ 1234g x100% = 18.64% Eggs 40g ÷ 1234g x100% = 3.24% Vanilla 12g ÷ 1234g x100% = 0.98% Chocolate Chips 340g ÷ 1234g x100% = 27.55% Total 1234g 100.01%

Adding things up

% Composition in Chemistry

 So far we have calculated a lot of molar masses  NaCl is Na 22.99g/mol Cl + 35.45g/mol = 58.44 g/mol

Adding things up

 Knowing this we can find what the percent of each

element is- all we have to do is divide by the total

and multiply by 100%

 NaCl

Na 22.99 ÷ 58.44 x 100% =39.34%

Cl + 35.45 ÷ 58.44 x 100% =60.66%

Adding up the %s should give VERY close to 100%