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# Moles PowerPoint PPT Presentation

Moles. Definition. A mole is the mass of a substance which contains the same number of particles as 12 grams of the isotope carbon 12 . These particles could be atoms, ions or molecules. 12 grams of carbon 12 contain 6.02 x10 23 atoms

Moles

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## Moles

### Definition

• A mole is the mass of a substance which contains the same number of particles as 12 grams of the isotope carbon12.

• These particles could be atoms, ions or molecules.

• 12 grams of carbon12 contain 6.02 x1023 atoms

• This number is the Avogadro Constant, and is given the symbol L.

Eg; One mole is…

16 + 2= 18g ofwater

63.5g of copper

27g ofaluminium

### Calculating the number of particles

• Number of particles = moles x Avogadro Constant.

• Eg; How many particles are there in 0.1moles of hydrogen?

• N = 0.1 x 6.02x1023 = 6.02 x 1022molecules.

### Calculating the number of moles

• Moles = number of particles / Avogadro constant.

• Eg; How many moles of methane are there in 3.01 x1023 molecules?

• Moles = 3.01x1023 / 6.02x1023 = 0.5 moles.

### Calculating the molar mass

• One mole of an element has a mass equal to the relative atomic mass in grams.

• Eg; the mass of one mole of sodium is 23g.

• The mass of one mole of a compound is found by adding together the masses of all its elements in the correct ratio.

• Units gmol-1

• Eg; What is the molar mass of calcium carbonate?

• Write the formula; CaC03.

• M = RAMCa+ RAMC + 3xRAMO.

• M = 40 + 12 + 3x16 = 100g

### Calculating the number of moles

• No moles = mass / RAM

• Eg; How many moles are there in 4g of calcium.

• Look up the mass number of calcium in the periodic table.

• The atomic mass is the mass number in grams.

• N = 4 / 40 = 0.1 moles

Think of the equation as a triangle

Mass (g)

m

Relative atomic mass

RAM

n

Number of moles

Rearranging;

n = m / RAM

mass (g)

m

Number of moles =

Relative atomic mass

RAM

n

### Calculating the number of moles of a compound.

• No moles = mass / Mr

• Eg; How many moles are there in 15g of calcium carbonate?

• Look up the Ars, then add them together to find the Mr.

• Mr = 40 + 12 + (16 x 3) = 100

• One mole has a mass of 100g.

• N = 15 / 100 = 0.15 moles.

Rearranging;

m = nRAM

mass =

m

n

RAM

Number of moles

X

RAM

### Calculating the mass from moles

• Mass = No moles X Ar

• Eg; What is the mass of 0.75 moles of sodium?

• Ar = 23

• Mass = 0.75 x 23 = 17.25g

• Similarly for a compound;

• Mass = No moles X Mr

• Eg; What is the mass of 0.8 moles of sodium chloride?

• Mr = 23 + 35.5 = 58.5

• Mass = 0.8 x 58.5 = 46.8g