C.5 Flashcards
What is the equation for a metal and oxygen reaction?
metal + oxygen –> metal oxide
e.g. - magnesium + oxygen –> magnesium oxide
What type of reaction is a metal + oxygen reaction?
An oxidation reaction as the metal has gained oxidation and become oxidised.
What is the equation for a metal and water reaction?
metal + water –> metal hydroxide + hydrogen
e.g. potassium + water –> potassium hydroxide + hydrogen
What metals react with water?
Potassium, sodium and lithium react vigorously and rapidly in water, calcium reacts fairly rapidly in water.
What metals do not react in water?
Magnesium, zinc, iron and copper. A reactivity series can be constructed based off of these reactions but a reaction with dilute acid is needed to order these 4 metals.
How do metals react with dilute acid?
- Potassium, sodium and lithium react dangerously fast
- Calcium reacts extremely vigourously
- Magnesium - rapidly
- Zinc - quite rapidly
- Iron - quite slowly
- Copper - no reaction
What two elements are added to the reactivity series and where are they?
Carbon and hydrogen. Carbon is considered more reactive than zinc but less than magnesium. Hydrogen is more reactive than copper only.
What happens to metals when they react in acid?
They lose electrons and form a positive ion. A metal’s reactivity is dependant on it’s ability to do this, therefore, group 1 and 2 elements are the most reactive as they have the fewest electrons to lose.
How are metals extracted from the earth?
Unreactive elements such as gold are found naturally in the Earth.
Metals such as iron and copper react with oxygen to form metal oxides, meaning displacement reactions are used to seperate them.
What element is usually used to displace metal oxides?
Carbon - as it is cheaper than most metals and more reactive than metals such as iron.
Give an example of using a displacement reaction to extract metals.
Carbon + iron oxide –> carbon dioxide + iron
- The carbon has been oxidised and the iron has been reduced
What is the difference between oxidation and reduction reactions?
Gaining oxygen = oxidation
Losing oxygen = reduction
What does oxidation and reduction mean in terms of electrons?
Oxidation means the LOSS of electrons (OIL)
Reduction means the GAIN of electrons (RIG)
What happens to acids in an aqueous solution?
They release positive hydrogen ions.
- e.g. HCl –> H+ + Cl-
H2SO4 –> 2H+ + SO4 2-
HNO3 –> H+ + NO3 -
What is a base?
A chemical (usually a metal oxide or hydroxide) which neutralises an acid, producing a salt and water.
What is an alkali?
An alkali is a base which is soluble in water. This means that all alkalis are bases, but not all bases are necessarily alkaline.
What happens to alkalis in an aqueous solution?
They release hydroxide ions (OH-)
Why do acids and alkalis neutralise each other?
The acid’s H+ ion and the alkalis OH- ion react to form water
What is the equation for a metal and acid reaction?
Metal + acid –> salt + hydrogen
Why do metals and acids react to form hydrogen and a salt?
All acids contain hydrogen, and as most metals are more reactive than hydrogen, they displace the hydrogen from it’s acid and become part of the salt.
What do different acids make when reacted with metal?
Hydrochloric acid –> metal chlorides
Sulfuric acid –> metal sulfates
Nitric acid –> metal nitrates
What metals are usually asked about in acid reactions and how do they react?
- Iron - reacts slowly as it is slightly more reactive than hydrogen
- Zinc - reacts faster than iron as it is further above hydrogen in the reactivity series
- Magnesium - reacts EVEN FASTER as it is EVEN FURTHER above hydrogen
What determines the rate of reactions between metals and acids?
How easily metal ions are produced.
What is the equation for the reaction between an acid and base/alkali?
Acid + base –> salt + water
- e.g. Hydrochloric acid + Copper oxide –> copper chloride + water
What do salts contain?
They contain a positive ion from the base or alkali and a negative ion from the acid.
What is the equation for a reaction between an acid and a metal carbonate?
Metal carbonate + acid –> a salt + water + carbon dioxide
What are the 3 main metal carbonates?
Sodium carbonate - Na2CO3
Calcium carbonate - CaCO3
Potassium carbonate - K2CO3
What can produce metal ions?
- Metals
- Metal oxides
- Metal hydroxides
- Metal carbonates
Draw a labelled diagram showing the equipment needed to produce a crystallised salt from a solution.
Learn the diagram 🙏
Describe the process to produce a crystallised salt from a solution. (Part 1)
- Set up the apparatus as shown
- Add a fixed volume of dilute sulfuric acid to the beaker which is the limting reactant
- Gently heat the acid until it is almost boiling
- Use a spatula to add a small amount of copper oxide powder to the acid. Stir using a glass rod
- The Copper Oxide will react in the solution, dissolve, and the solution will turn blue
Describe the process to form a crystallised salt from a solution. (Part 2)
- Stop adding Copper Oxide if powder remains after stirring as all the acid has now reacted.
- Use filtration to remove any unreacted copper oxide powder
- Add the solution to an evaporating basin and gently heat over a beaker of boiling water until 1/2 of the solution remains
- Leave for at least 24 hours in a cool place for crystals to form
- Scrape the crystals onto a paper towel and gently dry.
Bosh.
What do acid molecules do in an aqueous solution?
They ionise (split) and release H+ ions.
What is a strong acid?
An acid which fully ionises in an aqueous solution - meaning all of the molecules ionise.
What are 3 examples of strong acids?
Hydrochloric acid
Sulfuric acid
Nitric acid
How do we know an acid is strong?
If the arrow in the reaction equation is going in one direction, the acid is strong.
This shows no particulate is left behind as the strong acid fully ionises in an aqueous solution.
What is a weak acid?
An acid which only partially ionises in an aqueous solution.
Give three examples of weak acids.
Carbonic acid
Ethanoic acid
Citric acid
How do we know an acid is weak?
If the arrow in the reaction equation is a reversible reaction arrow, the acid is weak.
This is because some particulate still remains as the acid only partially ionises.
Why do strong acids have a lower pH than weak acids?
As all of the molecules of acid ionise, more hydrogen ions are formed, meaning the concentration of ionised acid is greater.
What is “order of magnitude”?
As the pH decreases by one unit, the concentration of hydrogen ions increases 10 times.
