Mass Moles and Molar Mass Read pp 80

Atomic Mass – the mass of one atom of an element (unit: u) Ex.

The Mole A mole is 6. 02 x 1023 entities (atoms or molecules) of

Molar Mass – the mass of one mole of a chemical entity (unit: g/mol)

Molar Mass What is the molar mass for: a) Na. Cl b) Ca. Cl

Performing calculations… m = mass (unit: g) n = mole (unit: mol) M =

Example 1 How many grams of Na. HCO 3 are in 0. 673 moles?

Example 2 How many moles of KMn. O 4 are there if you have

Example 3 Calculate the molar mass of an element, if 2. 220 mol has

Counting the number of atoms from mass How many atoms of silver are in

Counting the number of atoms from mass 1. Calculate amount of Ag (find mol)

Example 4 Count the number of nickel (Ni) atoms there are in one 5

Calculating the number of atoms in a compound Sand’s formula is Si. O 2

We want NO (# of oxygen atoms) NO = n. Si. O 2 x

Example 5 How many atoms of nitrogen are there in 1. 26 kg of

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Mass, Moles, and Molar Mass Read pp. 80 -105 (2. 1 and 22) Extension Questions p. 92 #1, 4, 8 -10 p. 106 #1 -10

Atomic Mass – the mass of one atom of an element (unit: u) Ex. Carbon is 12. 01 u; Hydrogen is 1. 01 u

The Mole A mole is 6. 02 x 1023 entities (atoms or molecules) of something (element or compound). The number 6. 02 x 1023 is known as Avogadro’s constant (NA). 6. 02 x 1023 carbon atoms weigh a total of 12. 01 g. 1 mol of magnesium atoms (6. 02 x 1023) weighs 24. 3 g. Notice something? ?

Molar Mass – the mass of one mole of a chemical entity (unit: g/mol) M=m n Remember to use a capital M for molar mass and a lowercase m for mass!

Molar Mass What is the molar mass for: a) Na. Cl b) Ca. Cl 2 M = 22. 99 g/mol + 35. 45 g/mol = 58. 44 g/mol M = 40. 08 g/mol + 2(35. 45 g/mol) = 110. 98 g/mol

Performing calculations… m = mass (unit: g) n = mole (unit: mol) M = molar mass (unit: g/mol)

Example 1 How many grams of Na. HCO 3 are in 0. 673 moles? m=nx. M = 0. 673 mol x 84. 01 g/mol = 56. 54 g

Example 2 How many moles of KMn. O 4 are there if you have 250 g of it? n=m/M = 250 g / 158. 04 g/mol = 1. 58 mol

Example 3 Calculate the molar mass of an element, if 2. 220 mol has a mass of 26. 66 g. Identify the element. M=m/n = 26. 66 g / 2. 220 mol = 12. 01 g/mol Element is Carbon

Counting the number of atoms from mass How many atoms of silver are in a 185. 3 g lump of pure silver? Two steps: 1. Calculate amount of X (find mol) 2. Calculate # of X atoms (find NX)

Counting the number of atoms from mass 1. Calculate amount of Ag (find mol) n. Ag = m / M = 185. 3 g / 107. 87 g/mol = 1. 72 mol 2. Calculate # of Ag atoms (find NAg) # of Ag atoms = 1. 72 mol x 6. 02 x 1023 atoms 1 mol = 1. 04 x 1024 atoms

Example 4 Count the number of nickel (Ni) atoms there are in one 5 -cent coin, which weighs 5. 0 grams. n. Ni = m / M = 5. 0 g / 58. 69 g/mol = 0. 085 mol # of Ni atoms = 0. 085 mol x 6. 02 x 1023 atoms 1 mol = 5. 12 x 1022 atoms

Calculating the number of atoms in a compound Sand’s formula is Si. O 2 (s). How many oxygen atoms are in a bag of pure sand, which contains 1000 g of Si. O 2? We know: m. Si. O 2 = 1000 g MSi. O 2 = 60. 09 g/mol 2 atoms O = 1 unit Si. O 2 1 mol Si. O 2 = 6. 02 x 1023 units

We want NO (# of oxygen atoms) NO = n. Si. O 2 x 6. 02 x 1023 units Si. O 2 x 2 atoms O 1 mol Si. O 2 1 unit Si. O 2 NO = 1000 g x 6. 02 x 1023 units Si. O 2 x 2 atoms O 60. 09 g/mol 1 mol Si. O 2 1 unit Si. O 2 NO = 2. 00 x 1025 atoms Note: Same principle as finding # of atoms for an element, but in this, you are adding in the # of atoms of the element in 1 unit of the compound (eg. always 2 O atoms in 1 unit of Si. O 2).

Example 5 How many atoms of nitrogen are there in 1. 26 kg of nitrogen gas? n. N 2 = m / M = 1260 g / 28. 02 g/mol = 44. 97 mol # of N atoms = 44. 97 mol x 6. 02 x 1023 molecules N 2 x 2 atoms N 1 molecule N 2 = 5. 41 x 1025 atoms