TEMA PARA LA MATERIA DE QUÍMICA...t/t

1. Understanding
Chemical
Reactions
QBA Miguel A. Castro Ramírez

2. The Mole

3. The mole
• The number of atoms in 1 gram of
hydrogen is called a mole.
• 1 gram of hydrogen contains approx. 6 X
1023 atoms.
• 600, 000, 000, 000, 000, 000, 000, 000
atoms – rather a lot!

4. The mole
• This number is
called
Avogadro’s
constant.

5. The mole
• One mole of any substance always
contains the same number of
particles.
• The mass of one mole of a substance
is called the Relative Atomic Mass
(RAM).

6. R.A.M.

7. • There are huge numbers of atoms
even in test-tube reactions.
• So it is easier to talk about moles
than the actual numbers involved.

8. Learn this equation!!!!
Moles of atoms = mass
R.A.M.

9. • It’s like cashing in 1p coins at the bank.
• If you take a thousand 1 p coins to your
bank, does the cashier count out each
coin?
• The coins are weighed out on scales. The
scales ‘know’ the mass of one hundred 1p
coins, and tell the cashier how many
pounds (£s) are on the scales.

10. Example
• How many moles of atoms are there
in 2.4 g of carbon?
• Moles of atoms = mass / RAM =
2.4/12 = 0.2 moles

11. Practice
Try these yourself!
How many moles are in:
1. 2g of hydrogen 2. 36g of carbon
3. 160g of oxygen 4. 1.4g of nitrogen
5. 0.19g of flourine?
(R.A.M.s H = 1, C = 12, O = 16,
N = 14, F = 19)

12. Answers
1. 2 moles 2. 3 moles
3. 10 moles 4. 0.1 moles
5. 0.01 moles

13. Relative Formula Mass
• Once you have a list of relative
atomic masses, (which are shown on
the Periodic Table), you can work out
the relative mass of any molecule.
• The relative atomic of CO2
• The RAM of C is 12
• The RAM of O is 16

14. Relative Formula Mass
• So for CO2 we have:
• 1 carbon = 1 X 12 = 12
• 2 oxygen = 2 X 16 = +32
• Therefore the relative formula mass
of carbon dioxide is 44.

15. Example
• What is the relative formula (or
molecular mass) of aluminium
sulphate, Al2(SO4)3
• (R.A.M.s: Al = 27, S =32, O =16)

16. Example
• What is the relative formula (or
molecular mass) of aluminium
sulphate, Al2(SO4)3
• (R.A.M.s: Al = 27, S =32, O =16)
• 342 g !

17. Questions
• Answer the questions off p175 of the
Chemistry text.