Chemical changes Flashcards
Thermal decomposition of metal carbonates gives you what products?
Metal oxide plus carbon dioxide
State the word equation for the thermal decomposition of copper carbonate.
Copper carbonate ——-> copper oxide plus carbon dioxide
State the word equation for the thermal decomposition of potassium permanganate
potassium permanganate ————> potassium mangnate + manganese oxide + oxygen
What happens to the atoms during a chemical reaction?
Chemical bonds are broken and the atoms rearrange themselves.
Atoms are not created or destroyed
What is an exothermic chemical reaction?
One which gives out energy - usually heat
What is an endothermic chemical reaction?
One which takes in energy - usually heat
What changes could you see during a chemical reaction which show that changes have happened?
- There may be a colour change eg blue hydrated copper sulphate becomes white anhydrous copper sulphate
- You could get a gas given off - bubbles or even smelly fumes
- You could get a solid made
- Some things would even explode!
What is oxidation?
It is the gain of oxygen
A chemical reaction between a substance and oxygen where the oxygen combines with the substance
A good example is the oxidation of iron
Iron + oxygen —-> iron oxide (rust)
What is combustion?
It is an oxidation reaction which happens when a substance is burned in oxygen (air)
eg magnesium ribbon which is a shiny metal burns to give a white powder - magnesium oxide
State the three things needed for combustion to occur
- Fuel
- Oxygen
- Heat
Carbon will burn in oxygen, identify the product and describe the flame
- Carbon dioxide
- Orange flame
Sulfur will burn in oxygen, identify the product and describe the flame
- sulfur dioxide
- pale blue flame
Iron will burn in oxygen, identify the product and describe the flame
- Iron oxide
- orange flame
Magnesium will burn in oxygen, identify the product and describe the flame
- Magnesium oxide
- bright white flame
What is a hydrocarbon?
It is a fuel consisting of atoms of carbon and hydrogen
Examples are, methane, butane and propane, coal, petrol and oil
They are used to provide energy when burned
eg
Methane + Oxygen ——-> carbon dioxide + water (+ energy)
the energy isn’t a product with atoms so it is in brackets!
Describe the test for oxygen
If oxygen is collected in a test tube it will relight a glowing splint
Describe the test for carbon dioxide
carbon dioxide will turn limewater milky/cloudy
Explain the term thermal decomposition
When a substance is heated the heat breaks down the chemical bonds and two or more new substances are formed
State the word equation for the thermal decomposition of copper (II) carbonate
Describe the colour change
Copper (II) carbonate —-> copper (II) oxide + carbon dioxide
The green carbonate becomes black oxide
State the word equation for the thermal decomposition of hydrated cobalt chloride
Describe the colour change
hydrated cobalt chloride —–> anhydrous cobalt chloride + water
Pink hydrated becomes blue anhydrous
What is reduction
the opposite of oxidation it is removal of oxygen from a compound
eg iron oxide + carbon ——-> iron + carbon dioxide
Explain how a metal can be extracted from it’s ore
An ore is a rock containing metal compounds often oxides. Carbon can be used to extract some metals from their ore using a reduction reaction
eg iron oxide + carbon ——-> iron + carbon dioxide
Explain the pH scale
Numbers from 0 to 14 which describe how alkaline or acidic a substance is.
0 being the strongest acid down to 6 the weakest. 7 is neutral so not acid or alkali
the weakest alkali is 8 and the strongest 14
What is an indicator?
Something which can show how acid or alkaline a substance is by changing colour
Describe how you would use universal indicator to test the pH of an unknown solution
- A solution is a liquid so put a few drops on to a white dimple tile
- Add a few drops of universal indicator solution
- Check the colour of the mixture against a colour chart.
Identify some indicators and their uses
- Litmus paper- acids turn red and alkalis blue
- Red cabbage water - acid red, neutral purple, alkali turquoise or yellow
- Universal indicator acid red to yellow depending on strength, neutral green, alkali blue to purple