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Conservation Of MassConservation Of Mass
L.O: To understand that atoms are never created or destroyed therefore mass of reactants = mass of products
Friday, April 21, 2023
Chemical ReactionsChemical 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 Do all atoms have a mass? Even gases?mass? Even gases?
Chemical ReactionsChemical 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 ReactionsChemical 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 Collect evidence to prove this hypothesisprove this hypothesis
In any reaction the total mass of products is the same as the total mass of the reactants
ExperimentsExperiments
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 1Practical 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 2Practical 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
ReactionsReactions
Practical 1 – copper sulfate + hydrochloric acid
Copper sulfate + Hydrochloric acid Copper chloride + Sulfuric acid
CuSO4 + 2HCl CuCl2+ H2SO4
ReactionsReactions
Practical 2 – magnesium + copper sulfate
Magnesium + Copper sulfate Magnesium sulfate + Copper
Mg + CuSO4 MgSO4 + Cu
The Equations – Team raceTEAM 1
Sodium + ___________ → Sodium Fluoride
________ + F2 → 2NaF
_________ + Chlorine → Lithium Chloride
2Na + F2 → _____________
Beryllium + Oxygen → _________
Be + O2 → _________
Calcium + Chlorine → _________
Ca + Cl2 → _________
TEAM 1
Sodium + ___________ → Sodium Fluoride
________ + F2 → 2NaF
_________ + Chlorine → Lithium Chloride
2Na + F2 → _____________
Beryllium + Oxygen → _________
Be + O2 → _________
Calcium + Chlorine → _________
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 togetherCl2
N2
HClNO2
CO2
CH4
MgOCuOCuSO4
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 H2O and H2O
Hydrogen + Oxygen Water
H
H
H
H
O
O
H
O
H
H
O
H
+
WaterLook at the following reaction
hydrogen + oxygen → water
H2 + O2 → H2O
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
WaterBut 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 method1. Write down the word equation2. Write the symbol equation3. 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
Balance The EquationsH2 + O2 → H2O
H2 + N2 → NH3
C3H8 + O2 → CO2 + H2O
Al + CuO → Al2O3 + Cu
K2O + H2O → KOH
CaCl2 + AgNO3 → AgCl + Ca(NO3)2
Balance The Equations2H2 + 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
21/04/23
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
Mg
OH Cl
Mg
ClCl
HH OH Cl
1 x magnesium, 1 x oxygen, 2 x hydrogen and 2 x chlorine atoms
Also 1 x magnesium, 1 x oxygen, 2 x hydrogen and 2 x chlorine atoms
C
H
H
H
HO
O
OO
OH H
OH H
CO
O
Example 2 – Burning methane
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