1.1 The Mole Concept 1.2 Formulas

Assessment Objectives Apply the mole concept to substances Determine the number of particles and the amount of substances (in moles) Define the terms relative atomic mass (A r ) and the relative molecular mass (M r ) Calculate the mass of one mole of a species from its formula Solve problems involving the relationship between the amount of substance in moles, mass and molar volume.

Assessment Objectives Apply the mole concept to substances Determine the number of particles and the amount of substance (in moles)

Measuring the amount of substance Imagine you have some water in a container. What things could you measure to tell people THE AMOUNT water you have? Volume Mass How about the NUMBER OF PARTICLES?

Numbers of Particles (or atoms) This is an extremely useful number to know……. Forms the basis of calculations in chemistry. But there is a problem because it is a REALLY BIG NUMBER. How big??????

Protons and neutrons have roughly the same mass. So, C weighs 12 u (atomic mass units). Calculate the actual mass of a C atom? (protons and neutrons each weigh about 1.7 x grams) Answer: approx. 2 x grams

How Big a Number??? Say I had 12g of Carbon How many atoms do you think are in 12g of carbon? There are 6.02 x atoms To simplify this really big number we say that 1 mole = 6.02 x atoms

Avogadros Number We call 6.02 x atoms AVOGADROS NUMBER I didn’t discover it. Its just named after me! 6.02 x is called “Avogadro’s Number” in honor of the Italian chemist Amadeo Avogadro ( ).

How big is 1 mole? How long would it take to spend a mole of 1 dirham coins if they were being spent at a rate of 1 billion per second?

Answer AED 6.02 x / AED = 6.02 x payments = 6.02 x seconds 6.02 x seconds / 60 = x minutes x minutes / 60 = x hours x hours / 24 = x 10 9 days x 10 9 days / = x 10 7 years A: It would take 19 million years

Assessment Objectives Define the terms relative atomic mass (A r ) and the relative molecular mass (M r )

Mass Atoms of different elements (or molecules, particles, ions etc ) weigh differently because they have different numbers of protons and neutrons. So 1 mole of different elements will have different masses.

Relative Atomic Mass (RAM) The RELATIVE Atomic Mass (A) of an element indicates how heavy an atom of an element is compared to an atom of a standard atom (C-12 is used as this standard and is assigned a value of exactly 12 g mol -1 ) So A(C) =12.01 g mol -1 A(Cl) = g mol -1

Relative Atomic Mass (RAM) Look at your periodic table………………. It turns out that: 1 mole of Lithium (Li) = 6.94g 1 mole of Nitrogen (N) = 14.01g Therefore 1 mole of elements = the RAM in grams Therefore, the Relative Atomic Mass can also be seen as g/mole

Relative Molecular Mass (M r ) Many elements do not exist as single atoms but are joined together in a MOLECULE. e.g Nitrogen (N) exists as a DIATOMIC MOLECULE (N 2 ) So: Nitrogen has a relative atomic mass of g mol -1 Nitrogen has a relative molecular mass of g mol -1

Molar Mass (M) The molar mass is very useful as it can be used for any substance (e.g. atoms, molecules, ions, compounds). It is determined by adding all masses of the atoms in the compound. E.g M (CO 2 ) = (2 x 16.00) =44.01 g mol -1 ( one atom of carbon and two atoms of oxygen) Note: for compounds it is sometimes referred to as FORMULA MASS

Assessment Objectives Calculate the mass of one mole of a species from its formula.

IMPORTANT! Formulas for compounds What do the numbers around the formula mean?? Cu(SO 4 ).5H 2 0 CaCl 2 The number out the front means that the molecule is multiplied (in this case 5 molecules of water). The subscript indicates that only the atom next to it ( or the ones in brackets) is multiplied (in this case there is one atom of Ca and 2 atoms of Chlorine)

Calculate the formula mass of magnesium carbonate, MgCO g g + 3(16.00 g) = g

Calculate the molar mass of the following: H 2 0 O 2 FeCl 3 Cu(SO 4 ).5H 2 0 Ca(NO 3 ) 2

Assessment Objectives Solve Problems involving the relationship between the amount of substance in moles, mass and molar mass.

Calculations This relationship cam be expressed as: Or rearranged as: M = m / n Relative Atomic Mass (g/mole) Mass (g) Number of moles m = n x M

How many grams of lithium are in 3.50 moles of lithium?

How many moles of lithium are in 18.2 grams of lithium?

If 3 moles of an element has a mass of 72.93, What element would it most likely to be?