Avogadro

1
Formula Equations and Moles

• Avogadros Constant
• What is it and what information does it give us?

2
Why are moles important?

• As scientists we add elements together to make
  new substances
• We like to work out the ratios before we do this
  so that there is no waste
• Example a food recipe, you dont want too many
  eggs as it will spoil the cake

3
What Avogadro did for us

• He worked out an exact figure for the quantity of
  carbon present in 12 grams
• This is a measure of the number of atoms present
• This allows us to compare atoms in terms of ratios

6.02 x 1023
4
Avogadros number
6.02 x 1023

• What does this number represent?
• Which element did it refer to?
• How many particles are present in 2 moles of Na?
• How many particles are present in 0.5 moles of
  Fe?
• How many moles are there in 4.167 x1014 of
  particles Pb?

5
Molecular formula

• What is meant by molecular formula?
• How can it be calculated?
• What is the molecular formula for
• water
• magnesium chloride
• potassium oxide
• silicon iodide

6
Empirical formula

• This is the simplest ratio
• is the molecular formula for ethene,
  but its empirical formula is C1 H2
• What is the empirical formula for

C2H4
C6H12O6
C4H8Cl2
CH3COOH
7
Calculating the empirical formula from the
percentage massesIf a compound gives the
following results when analysed, 87.7 C and
14.3 H

• What is the empirical and molecular formula?
• 87.7/12 7.1 carbon
• 14.3/1 14.3 hydrogen
• What is the lowest ratio between these numbers?

8
Molecular formulaIf a mass of a hydrocarbon
equals 42, what is the molecular formula?

• Work out the following
• the empirical formula equals C1H2

9
Concentration and Molarity

• What is a solute, solvent and a solution?
• What do we mean by the concentration of
  something? Write a sentence to express when
  something is more concentrated. Use the following
  words, volume, solute, solvent
• Can you remember the equation that calculates the
  concentration of a liquid?

Moles Conc x Volume
10
How do we measure liquid concentrations?

• When 1 mole of solute is dissolved in 1 decimetre
  of solution, its concentration is said to be 1
  mol dm-3
• This is called 1 M for short
• We measure concentration in molarity

1 dm3 1000cm3 1 litre
11
Work out how much compound would be needed to
make a 1 molar solution for the following

• .KHCO3
• .NaCl
• .Li2O

12
Example How many moles are there dissolved in
200 cm3 of 1 M solution of NaHCO3
200/1000 x 1 0.2 moles
13
Work out the molarity of questions 4-6

• 4.KHCO3 1 mole is dissolved in 2 litres of water
  1/2
• 5.NaCl 2 moles is dissolved in 500cm3 of water
  2/0.5
• 6.Li2O 0.5 moles dissolved in 1.5 dm3 of water
  0.5/1.5

14
How can we work out the amount of solid dissolved
in a liquid?
Work out the amount of solid dissolved in each
solution Example Work out the number of moles
the times by the mass 200/1000 x 1M 0.2 moles
of LiOH
0.2 x 24 (Li 7 and OH 17, 7 17 24)
1.2 grams of LiOH
15
Calculate the following

• .KHCO3 1 mole is dissolved in 2 litres of water
• .NaCl 2 moles is dissolved in 500cm3 of water
• .Li2O 0.5 moles dissolved in 1.5 litres of water

16
The purpose of a titration

• To find the concentration of a unknown solution
• Comparing the unknown to a known solution
• Helps us calculate the amount of acid or alkali
  present
• When would this be used in the real world?

17
You have created a known molarity for the alkali
sodium hydroxide

• Work out the mass of NaOH
• Na 23 O 16 H 1 add together 40
• Molarity 250/1000 0.25 0.25/0.25
  1.0 molar or 1M
• Now you can work out the molarity of the unknown
  substance
• Measure a known volume of acid and add indicator
• Neutralise the acid
• What equation would you use?

18
Results Vol acid 25cm cubedVol alkali needed
to neutralise 26.5 cm cubed Conc of alkali
0.95 molar
Molarity of known substance x Volume Molarity
of unknown substance x volume
Substitute in what you know 0.95 x 26.5 ? x 25
1.007
19
Equations

• Write a balanced equation for the reaction
  between hydrochloric acid and sodium hydroxide
• Follow this with an ionic equation

NaOH (aq) HCl (aq) NaCl (aq) H2O (l)
20
For the following examples balance the equation
putting state symbols

• .NH3 O2 NO2 H2O
• .C2H5OH O2 CO2 H2O
• .Al NaOH Na3AlO3 H2
• .CO2 H2O C6H12O6 O2
• .C3H8 O2 CO2 H2O
• .4Al 12H2SO4 2Al2(SO4)3 6SO2 12H2O

21
You have just done an experiment and made
Ammonium Sulphate. You started out with 8.6g of
Ammonium hydroxide.

• What would you react this with to make a
  sulphate? What is the new class of substance you
  have made? What is this type of reaction called?
• What is the maximum amount you could make?
• Hint Moles mass/ molecular mass
• You also need to work out the products and ratios
  in the reaction first.
• Now calculate the actual yield when
• The experimental value of the substance is 10.64g
  How did I work this out?
• Hint you need to compare it to your 100
  theoretical

22

• The experiment was done again, the yield went up
  to 83, what was the amount made?
• What could have been done differently? Why will
  you always not get less than 100 yield no matter
  how careful you are?

23
Example 2NH4OH H2SO4 (NH4)2 SO4 2H2O

• Look at what changes in the ions, first you will
  need to write out the ions as they exist
• Cancel out the ones that dont change.
• Then construct an equation will the essential
  ions present only.
• Try this one now using the same rules

CaCO3 HCl CaCl2 CO2 H2O
Mg 2HCl MgCl2 H2
24
Working out reacting gas amounts

• What equation do we use to calculate gas
  quantities?
• If 1.5 dm cubed of Hydrogen was produced from
  hydrochloric acid when magnesium dissolved, how
  much magnesium was there to start with?
• Hint- start with the equation

25
Equal volumes of all gases at the same pressure
and temperature contain the same number of
particles (same number of moles)
26

• Work out the moles of potassium nitrate
• Work out the volume of oxygen produced

27

• .Calculate how many dm3 of hydrogen gas are
  produced when
• 19.5g of zinc metal dissolved in excess
  hydrochloric acid at
• 30oC and 100 KPa.
• .C8H18 O2 CO2 H2O

Balance this What volume of oxygen reacts with
10 dm3 of petrol? How many moles of petrol are
there? How many moles of oxygen are
required? What is the mass of CO2 produced?
28
Calculate the volume of gas produced when 150g of
calcium carbonate decomposes to form calcium
oxide and carbon dioxide in dm3 at 100 KPa and
25oC
Hard water from a towns water supply was
measured and found to be 0.4g in 1m3 (The
calcium carbonate was weighed after the water
was boiled off).

• Calculate
• Work out the number of moles present
• Work out the molarity
• The calcium carbonate was reacted with sulphuric
  acid, write a balanced symbol equation for this
  putting in the number of moles of each and the
  masses

29
H2SO4 CaCO3 CaSO4 CO2 H2O

• Write a ionic equation for this reaction
• An organic compound is shown to have 40 carbon,
  6.7 hydrogen and 53.3 oxygen
• Deduce the empirical formula
• It is shown to have a mass of 180, deduce the
  molecular formula

30

• A company that makes vinegar has to print the
  percentage amount of organic acid on their
  bottles, a reaction between sodium hydroxide was
  undertaken. 25 cm3 reacted with 29cm3 of 0.1 M of
  the alkali.
• Work out the concentration
• The amount of carbon was found to be 48.7,
  hydrogen was 8.1 and oxygen was 43.2, work out
  the empirical formula
• The mass of the acid is 74, work out the formula
• Write an equation for the neutralization
  reaction, what is the name of this acid?

31
Greenhouse gases

• What is the relationship, if any?
• What is the amount of gases measured in?
• Explain what the greenhouse effect is
• What other proof is there available that CO2 has
  an effect on the atmospheric temperature?
• Answer Venus atmosphere is 96 CO2 and the temp
  is 450oC

32

• Which gases cause the most warming of the planet?
• Which are the most abundant greenhouse gases?

33

• On earth, the most abundant greenhouse gases are,
  in order of relative abundance
• water vapor
• carbon dioxide
• methane
• nitrous oxide
• ozone
• CFCs
• The most powerful greenhouse gases are
• water vapor, which causes about 3670 of the
  greenhouse effect on Earth. (Note clouds
  typically affect climate differently from other
  forms of atmospheric water.)
• carbon dioxide, which causes 926
• methane, which causes 49
• ozone, which causes 37

34
Work out the percentages present in the double
salt

• Ammonium iron (II) Sulphate can be made from
  iron, ammonia and sulphuric acid.
• Write the individual equations for each
• If 25cm3 of 1.0 M H2SO4 is used work out the mass
  of FeSO4 made from 1.12g of Fe
• The remainder of the acid reacts with the
  ammonia, work out the mass of ammonium sulphate
  made.
• The total mass of the dried combined salts is
  2.8g, workout the 100 theoretical mass then
  calculate what the yield is?

35

• Fe H2SO4 FeSO4 H2
• Mass 1.12g 1.96 3.04
  ?
• Moles 0.2 0.025
  0.2 ?
• 2NH3 H2SO4 (NH4)2SO4
• Mass ? ?
  ?
• Moles ? 0.005
  ?
• Work out the missing masses and moles