*11 Chemical Changes Flashcards
What is a physical change?
A change in which no new substance is formed.
What is a chemical change?
A change in which new substances in the form of elements or compounds are formed.
State one difference between a chemical change and a physical change.
Besides the fact that chemical changes produces new substances.
Chemical changes are irreversible while physical changes are reversible.
Reversible means the mixture can usually be seperated easily by separation techniques.
Look at the word equation below:
methane + oxygen —–(heat)—–> carbon dioxide + water
Identify the reactants and products in this chemical reaction.
reactants: methane, oxygen
products: carbon dioxide, water
Look at the number of atoms before and after a chemical reaction.
What can you conclude about the relationship between the number of atoms before and after the reaction?
The number of each type of atoms remains the same.
Both before and after the reaction:
There are 4 hydrogen atoms, 4 oxygen atoms and 1 carbon atom.
What is combustion?
aka burning in air
It is a chemical reaction in which a substance is heated in the presence of oxygen to form one or more new substances.
e.g.
carbon + oxygen –(heat)—> carbon dioxide
What is thermal decomposition?
It is a process in which a substance is broken down into 2 or more simpler substances upon heating.
e.g.
calcuim carbonate —-(heat)—-> calcium oxide + carbon dioxide
What is oxidation?
A chemical change is which a substance gains oxygen.
Rusting and cellular respiration are some examples of oxidation.
e.g.
iron + oxygen + water ——> rust
What is the difference between oxidation and combustion?
Oxidation does not require heat while combustion requires heat to happen.
What is neutralisation?
A reaction where acid mixes with alkali to form salt and water.
e.g.
hydrochloric acid + sodium hydroxide ———> sodium chloride + water
State 2 properties of acid.
Think taste, litmus test
1) have a sour taste
2) turns blue litmus paper red
State 2 properties of alkali.
Think taste, litmus test
1) have a bitter taste
2) turns red litmus paper blue
Give three examples of acid found in the lab.
1) hydrochloric acid
2) nitric acid
3) sulphuric acid
Give three examples of alkalis found in the lab.
1) sodium hydroxide
2) calcium hydroxide
3) potassium hydroxide
Note that the names of alkalis usually ends with hydroxide.
The reaction below shows a neutralisation.
hydrochloric acid + calcium hydroxide –> salt + water
Identify the name of the salt.
The name of the salt takes one part from the acid and one part from the alkalis.
calcium chloride
calcium from the alkalis and chloride from the acid
What are the products of an acid-metal reaction?
Think: metal + acid —–> ??
salt and hydrogen
Use this acronym to remember:
MASH
Metal Acid Salt Hydrogen
Describe the test for hydrogen gas.
Introduce a lighted splint to the gas. Hydrogen burns with a ‘pop’ sound.
What are the products of an acid-carbonate reaction?
Think: carbonate + acid —–> ??
salt, water and carbon dioxide
Use this acronym to remember
CACoWS
Carbonate Acid Carbon dioxide Water Salt
Describe the test for carbon dioxide gas.
Bubble the gas through lime water. Carbon dioxide gas produces a white precipitate in lime water.
Do not use limewater turns milky or chalky.
The pH scale ranges from 0 to 14.
What is the pH ranges of acidic solutions?
What is the pH ranges of alkaline solutions?
What is the pH value of neutral solutions?
acidic soluions: 0 to 6.9
alkaline solutions: 7.1 to 14
neutral solutions: 7
How do we test that a solution is neutral using only litmus paper?
Both the blue and red litmus paper must be used.
A blue litmus paper remains blue and a red litmus paper remains red in a neutral solution.
How do we test that a solution is acidic using only litmus paper?
A blue litmus paper turns red in an acidic solution.
How do we test that a solution is alkaline using only litmus paper?
A red litmus paper turns blue in an alkaline solution.
What is the pH value of a solution after neutralisation?
Think: Why is this process called neutralisation?
pH 7
