Download H 2 and H 2 + O 2 g H 2 O and H 2 O Hydrogen + Oxygen g Water

Thursday, May 4, 2017
Conservation Of Mass
L.O: To understand that atoms are never created or destroyed
therefore mass of reactants = mass of products
Chemical Reactions
 What are the signs that a chemical reaction has taken place?
 There are usually some obvious changes during a chemical
reaction, including:  A change in colour
 A gas coming off (you may see fizzing or bubbling)
 A change in temperature (the reaction mixture may get hotter)
 A solid may be formed when two solutions are mixed
together
Do all atoms have a mass?
Even gases?
Chemical Reactions
 New substances are formed by chemical reactions – when
elements react together to form compounds their atoms join to
other atoms via chemical bonds
 For example:  Iron and sulfur react together to form a compound called iron
sulfide
Mixture of powered iron
(grey) + sulfur (yellow)
Mixture is heated
A chemical reaction occurs,
forming iron sulfide
Chemical Reactions
 New substances are formed by chemical reactions – when
elements react together to form compounds their atoms join to
other atoms via chemical bonds
 Chemical bonds involve electrons from the reacting atoms – bonds
can form when:  Electrons are transferred from one
atom to another, so that one atom
gives electrons and the other takes
electrons
 Electrons are shared between two
atoms
Potassium Iodide + Lead nitrate  Lead Iodide +Potassium Nitrate
2KI + Pb(NO3)2  PbI2 + 2KNO3
Collect evidence to prove
this hypothesis
In any reaction the total mass of products is the same as
the total mass of the reactants
Experiments

How could you design a practical to test the conservation of mass hypothesis - in
any reaction the total mass of products is the same as the total mass of the
reactants?

You are going to complete 2 experiments looking at how mass remains the same
from the start of the reaction to when it finishes

It is vital you measure accurately the mass of reactant(s) and product(s)

*In some reactions it may appear the mass has increased / decreased – this is due
to the addition of atoms (e.g. oxygen has bound from the atmosphere) / loss of
atoms to the atmosphere (e.g. carbon dioxide has been produced and released into
the atmosphere).

*For this reason it is vital you consider how you would collect gas which may be
formed / control gas which may be added to the experiment
Practical 1
 Complete the following practical, ensuring you identify the mass
of reactants and products (remember, we want to see if there was
any change in mass)!
 Measure out 50ml of hydrochloric acid (HCl) into a beaker (find its
mass)
 Measure out 50ml of copper sulfate (CuSO4) into a beaker (find its
mass)
 Mix the two liquids – what is the final mass
Write a word and balanced symbol equation for the reaction
Practical 2
 Complete the following practical, ensuring you identify the mass
of reactants and products (remember, we want to see if there was
any change in mass)!
 Measure out 50ml of copper sulfate (CuSO4) into a beaker (find its
mass)
 Take 2g of magnesium (Mg) and add this to the copper sulfate
 What is the final mass?
Write a word and balanced symbol equation for the reaction
Reactions
 Practical 1 – copper sulfate + hydrochloric acid
Copper sulfate + Hydrochloric acid  Copper chloride + Sulfuric acid
CuSO4 + 2HCl  CuCl2+ H2SO4
Reactions
 Practical 2 – magnesium + copper sulfate
Magnesium + Copper sulfate  Magnesium sulfate + Copper
Mg + CuSO4  MgSO4 + Cu
The Equations – Team race
TEAM 1
TEAM 1
Sodium + ___________ → Sodium Fluoride
Sodium + ___________ → Sodium Fluoride
________ + F2 → 2NaF
________ + F2 → 2NaF
_________ + Chlorine → Lithium Chloride
_________ + Chlorine → Lithium Chloride
2Na + F2 → _____________
2Na + F2 → _____________
Beryllium + Oxygen → _________
Beryllium + Oxygen → _________
Be + O2 → _________
Be + O2 → _________
Calcium + Chlorine → _________
Calcium + Chlorine → _________
Ca + Cl2 → _________
Ca + Cl2 → _________
See if you can work out what these letters and numbers mean,
the first one has been done for you. Then can you name the
elements or compounds?
O2 – 2 Oxygen atoms joined together
Cl2
N2
HCl
NO2
CO2
CH4
MgO
CuO
CuSO4
CaCO4
Balancing
 It is key you know how to balance the equations!
 Remember: there must always be the same number of atoms on
both sides
 Numbers can only be put in front of the formula when it is
needed e.g. 2CO2 means two molecules of carbon dioxide
H2 and H2 +
O2 g
H2O and H2O
Hydrogen + Oxygen g Water
Water
Look at the following reaction
hydrogen + oxygen → water
H 2 + O2 → H 2 O
 Again there is a problem – this time we have an oxygen atom
missing from the right hand side
 To balance this, we can add a number in front of the right hand
side
H2 + O2 → 2H2O
Water
But this is still unbalanced!
hydrogen + oxygen → water
H2 + O2 → 2H2O
 Finally, we can add a number in front of the hydrogen on the left
hand side, to balance this up
2H2 + O2 → 2H2O
Balancing – A simple method
Write down the word equation
2. Write the symbol equation
3. Choose one element and count how many atoms of
that element there are on each side of the equation.
4. If the numbers do not match you will need more of
one of the chemicals. You must write a 2 in front of
the chemical which you want more of.
5. Repeat steps 2 and 3 checking the other atoms, you
may need to have several molecules of one chemical
to balance it.
Try this: Copper reacting with oxygen
1.
Balance The Equations
H2 + O2 → H2O
H2 + N2 → NH3
C3H8 + O2 → CO2 + H2O
Al + CuO → Al2O3 + Cu
K2O + H2O → KOH
CaCl2 + AgNO3 → AgCl + Ca(NO3)2
Balance The Equations
2H2 + O2 → 2H2O
3H2 + N2 → 2NH3
C3H8 + 5O2 → 3CO2 + 4H2O
2Al + 3CuO → Al2O3 + 3Cu
K2O + H2O → 2KOH
CaCl2 + 2AgNO3 → 2AgCl + Ca(NO3)2
Conservation of mass in reactions
In any reaction the total mass of products is the same as the total
mass of the reactants
Example 1 – Magnesium oxide and hydrochloric acid
H
Mg
Cl
O
H
Cl
Mg
Cl
1 x magnesium, 1 x oxygen, 2 x
hydrogen and 2 x chlorine atoms
H
Cl
Also 1 x magnesium, 1 x oxygen, 2 x
hydrogen and 2 x chlorine atoms
Example 2 – Burning methane
H
H
04/05/2017
H
O
C
H
O
O
O
O
O H
H
O
C
O
H
O
H
H