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