Conservation Of Mass L.O: To understand that atoms are never created or destroyed therefore mass of reactants = mass of products Wednesday, October 14, 2015

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 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 heatedA 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(NO 3 ) 2  PbI 2 + 2KNO 3

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 (CuSO 4 ) 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 (CuSO 4 ) 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 CuSO 4 + 2HCl  CuCl 2 + H 2 SO 4

Reactions  Practical 2 – magnesium + copper sulfate Magnesium + Copper sulfate  Magnesium sulfate + Copper Mg + CuSO 4  MgSO 4 + Cu

The Equations – Team race TEAM 1 Sodium + ___________ → Sodium Fluoride ________ + F 2 → 2NaF _________ + Chlorine → Lithium Chloride 2Na + F 2 → _____________ Beryllium + Oxygen → _________ Be + O 2 → _________ Calcium + Chlorine → _________ Ca + Cl 2 → _________ TEAM 1 Sodium + ___________ → Sodium Fluoride ________ + F 2 → 2NaF _________ + Chlorine → Lithium Chloride 2Na + F 2 → _____________ Beryllium + Oxygen → _________ Be + O 2 → _________ Calcium + Chlorine → _________ Ca + Cl 2 → _________

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? O 2 – 2 Oxygen atoms joined together Cl 2 N 2 HCl NO 2 CO 2 CH 4 MgO CuO CuSO 4 CaCO 4

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. 2CO 2 means two molecules of carbon dioxide

H 2 and H 2 + O 2  H 2 O and H 2 O Hydrogen + Oxygen  Water

Water Look at the following reaction hydrogen + oxygen → water H 2 + O 2 → 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 H 2 + O 2 → 2H 2 O

Water But this is still unbalanced! hydrogen + oxygen → water H 2 + O 2 → 2H 2 O Finally, we can add a number in front of the hydrogen on the left hand side, to balance this up 2H 2 + O 2 → 2H 2 O

Balancing – A simple method 1. 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

Balance The Equations H 2 + O 2 → H 2 O H 2 + N 2 → NH 3 C 3 H 8 + O 2 → CO 2 + H 2 O Al + CuO → Al 2 O 3 + Cu K 2 O + H 2 O → KOH CaCl 2 + AgNO 3 → AgCl + Ca(NO 3 ) 2

Balance The Equations 2H 2 + O 2 → 2H 2 O 3H 2 + N 2 → 2NH 3 C 3 H 8 + 5O 2 → 3CO 2 + 4H 2 O 2Al + 3CuO → Al 2 O 3 + 3Cu K 2 O + H 2 O → 2KOH CaCl 2 + 2AgNO 3 → 2AgCl + Ca(NO 3 ) 2

Conservation of mass in reactions 14/10/2015 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 O H Cl Mg Cl H H O H 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 H O O O O O H H O H H C O O Example 2 – Burning methane