# Unit 6 Moles Conversions Formulas. Mole SI base unit for measuring the amount of substance The number of representative particles in exactly 12 grams.

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Unit 6 Moles Conversions Formulas

Mole SI base unit for measuring the amount of substance The number of representative particles in exactly 12 grams of pure carbon-12 1 mole = 6.02 x 10 23 representative particles

Avogadro’s Number 6.02 x 10 23 is called Avogadro’s number It is the number of representative particles equal to 1 mole A representative particle is any kind of particle and depends on the substance – Water = molecule – Copper = atom – NaCl (salt) = formula unit

Molar/Formula Mass Molar/Formula mass is the mass in grams of 1 mole of any pure substance. – units are g/mol Molar mass is equal to the atomic mass on the periodic table Gram atomic mass: (found on periodic table) – Ex: C = 12.011 amu This means 1 mole of Carbon = 12.011 g

Let’s practice: Find the # of grams 1 mole of the following is equal to – Al –H–H –O–O –P–P

Formula Mass/Molar Mass Formula or Molar mass is the mass of 1 mole of a pure substance H 2 O – covalent compound (nonmetal/nonmental) H=2x1 g= 2 g O=1x16 g= 16 g total = moles x avg. atomic mass = 18 g

Let’s practice: Find the # of grams 1 mole of the following is equal to – H 2 O 2 – Sodium chloride – Calcium nitrate – (NH 4 ) 3 PO 4 – Dinitrogen tetraoxide

Percent Composition You can calculate the percentage of a certain element in a compound Use the % Formula: (Part/Whole) x 100 = 1 st - we need the formula mass or the whole 2 nd – we need the part found in the compound 3 rd – divide and multiple by 100

Example: What is the % of Hydrogen in H 2 O? 1 st : Gram atomic Mass – H 2 O – covalent compound (nonmetal/nonmental) H=2x1= 2 O=1x16= 16 total = moles x avg. atomic mass = 18 g 2 nd : Hydrogen has a mass of 2g total 3 rd : %H = (2g/18g) x 100 = 11.11%

What is the percent of oxygen in in H 2 O? The percent of each element in a compound should add and equal 100.

Lets practice: Find the percent composition of each of the elements in the following compounds. – Fe 2 O 3 – Copper (I) sulfide

Molar Mass can be used as a Conversion Factor What is the mass in grams of 2.5 mol of NaCl? Steps – 1 st : get the formula/molar mass of the compound – 2 nd : convert Na= 1 x 23 = 23 Cl = 1 x 35.5 = 35.5 = 58.5g ?g = 2.5 mol NaCl58.5 g NaCl=146 g NaCl 1 mol NaCl

Avogadro’s number as a conversion factor 1 mole = 6.02 x 10 23 representative particles Representative particles can be atoms, molecules, particles, formula units, pieces, etc How many molecules are in 3.5 moles of CO 2 ? ?molecules = 3.5 mol CO 2 6.02 x 10 23 molecules = 1 mol NaCl 2.1 x 10 24 molecules CO 2

Volume Conversions At STP 1 mol = 22.4 liters of a gas What volume will 54.6 grams of CO 2 occupy at STP? ?liters = 54.6 g CO 2 1 mol CO 2 22.4 liters CO 2 = 44 g CO 2 1 mole CO 2 27.8 liters of CO 2

Bell Work Complete the following on a NEW sheet of paper to TURN IN! 1.How many grams are in 0.817 moles of C 2 H 2 O 6 ? 2.How many moles are in 60 grams of CaC0 3 ? 3.How many formula units of CaCl 2 are in 45 grams? 4.How many molecules of CO 2 are in 4.3 moles?

Empirical & Molecular Formulas Empirical Formula - the simplest whole number formula/ratio of a compound. This means the equation cannot be reduced anymore. (Smallest whole number ratio) Molecular Formula – the actual or true formula of the compound – indicates the actual number of atoms in the compound Sometimes the empirical and molecular formula are the same. If they are different the molecular is ALWAYS larger.

Calculating Empirical Formulas Example: An unknown sample contains 25% H and 75% C. What is the empirical formula?

Steps: 1 st Convert % to grams (Assume you have 100 grams total) 2 nd Convert grams to moles by using the atomic mass 25 % = 25 grams H 75 % = 75 grams C 25 % = 25 g H x (1mol H/1g H) = 25 mol H 75 % = 75 g C x (1mol C/12 g C) = 6.25 mol O

3 rd Divide by the smallest # of moles to get the ratio 4 th Put numbers as subscripts of elements in formula 5 th if a whole number is not found after dividing, multiply by a factor to make it a whole # (must multiply all numbers by the same factor) H = 25 mol/ 6.25 mol = 4 C = 6.25 mol / 6.25 mol = 1 CH 4

Molecular Formula Indicates the actual amount of atoms present Must have molecular weight to determine molecular formula

Determining Molecular Formula Steps: 1.Determine the empirical formula 2.Determine the empirical weight (molar mass of the empirical formula) 3.Divide the molecular weight given by the empirical weight you calculated – If one, then the empirical formula is the same as the molecular formula

4.If the answer from step 3 is a whole number, then take the answer and multiply all subscripts in the equation by the number. 5.If it is not a whole number you must multiple by a factor to make it a whole number then multiply each of the subscripts by it. This will give the molecular formula.

Molecular Formula Example What is the molecular formula of a compound with a molecular mass of 64 g/mol and an empirical formula of CH 4 ? CH 4 empirical mass = (12) + (4 x 1) = 16g/mol Molecular mass = 64 g/mol 64 / 16 = 4 Multiply subscripts by 4 New formula is C 4 H 16

Hydrates A compound that contains a certain amount of water molecules Example:CuSO 4. 5H 2 O Copper sulfate pentahydrate Hydrates can be dehydrated by heating The dehydrated form can be used to absorb moisture from the air – like those packets you find in your shoe boxes – deliquescent

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