C5-Chemical Changes Flashcards
How is the reactivity of metals decided
- When metals react they lose electrons and form positive ions
- The reactivity of a metal is decided by how easy or hard it is for that metal to lose electrons
How are unreactive metals extracted
Unreactive metals are extracted in their native state in the ground
How are more reactive metals extracted found in the ground
More reactive metals are found in the ground as metal oxides as they have reacted with oxygen in the ground
How are these more reactive metals extracted
These more reactive metals are extracted by a more reactive element dispacing it from its compound
This is usually carbon as other elements are more expensive so not used. If the metal is more reactive than carbon it is extracted by electrolysis
What is an example of a reaction for the extraction of a more reactive metal
Iron oxide + carbon —> carbon dioxide + iron
The iron is reduced
F2+ + 2e- = Fe
Carbon has been oxidised
C+ 2e-=C2+
What is oxidation in terms of electrons
Oxidation is loss of electrons
E.g if an atom turns into an ion
What is reduction in terms of electrons
Reduction is gain of electrons
For example if an ion turns into an atom
What do all acids contain
All acids contain hydrogen
How do metals react with acid
Metals higher than hydrogen in the reactivity series displace hydrogen when they react with an acid to form a salt of their metal
What is the equation for the reaction of acids and metals
Metal + acid —-> salt + hydrogen
What type of salt does hydrochloric acid form
Hydrochloric acid forms salts ending in chloride
What type of salt does sulphuric acid form
Sulphuric acid forms acids ending in sulphate
How is the speed of the reactions with the metals decided
The further away a metal is on the reactivity series from hydrogen , the more fast it reacts
What types of ions do acids produce in an aqueous solution
Acids produce hydrogen ions in aqueous solutions
What are bases
Bases are chemicals that can neutralise an acid to produce a salt and water
What are soluble bases called
Soluble bases are called alkali’s
What is the PH scale and how can it be measured
The PH scale is a scale that tells the acidity or alkalinity of acids
It can be measured using universal indicator or a PH probe
Alkalis have a PH of 8-14
Neutral solutions have a PH of 7
Acids have a PH of 0-7
What is the equation for a neutralisation reaction
H+ + OH- = H20
The OH is produced by the alkali and the hydrogen is produced by the acid.
The solution produced has a Ph of 7 and is neutral
What happens to a strong acid in an aqueous solution
A strong acid in an aqueous solution fully ionises and the reaction is not reversible
-Strong acids have a lower PH than weaker acids
What happens to weaker acids in aqueous solutions
Weaker acids only partially ionise in aqueous solutions and the reaction is reversible
What happens to the hydrogen ions in a solution as the PH decreases
For every PH decrease the amount of hydrogen ions increases 10 times
-Strong acids will have lower PH’s as the atoms are fully ionised so their are more hydrogen ions
How does the concentration of an acid affect the PH
The concentration of an acid tells us the amount of acid in a given volume of solution. A dilute acid will have less molecules of acid for a given volume of solution than a comcentrated acid .
(You can have a dilute strong acid that is not concentrated)
PH will decrease with increasing concentration
What happens when a base or alkali reacts with an acid
When a base or alkali reacts with an acid it produces a salt and water
What sort of ions does the salt from this reaction contain
The salt from this reaction contains positive ions from the base and negative ions from the acid
Hydrochloric acid —-> chlorides
Nitric acid —-> nitrates
Sulfuric acid —-> sulphates
What happens when metal carbonates react with acids
When metal carbonates react with acid they produce a salt , water and carbon dioxide
Metal carbonate + acid —> salt + water + carbon dioxide
What colours do indicators turn depending on what type of solution is being tested
If an acid is present the indicator will turn red
If an alkali is present the indicator will turn towards purple
Describe the steps in a titration reaction
- Use a pipette to transfer 25cm3 of sodium hydroxide solution into a conical flask( make sure to let all of the solution drain out of the pipette)
- Add 5 drops of indicator to the solution to the alkali in the conical flask
- Place the conical flask on a white tile so you can see the colour change more clearly
- Fill a burette with an acid and add it to the alkali until the solution is neutral. When you start to see a colour change add the acid to the solution drop by drop until the solution is neutral
- Record the final volume of acid in the burette and use the initial volume to work out the amount of acid used in the neutralisation
- Repeat the experiment until you get two readings within 0.1cm3 of each other
Describe the steps in Making a soluble salt
Start with a fixed volume of dilute sulfuric acid. This is the limiting reactant
Gently heat the acid until almost boiling
Use a spatula to add small amounts of copper oxide to the acid
The copper oxide will react and seem to disappear (solution will be blue as that is colour of copper sulphate )
Stop adding copper oxide when the copper oxide powder stays after stirring . At this point the reaction has stopped
Use filtration to filter out the excess copper oxide
Place the solution in an evaporating basin and heat gently over boiling water until roughly half the solution remains
Leave the copper sulphate for 24 hours in a cool place so copper sulphate crystals can form
Scrape the crystals onto a paper towel and leave them to dry
How can you measure the reactivity of metals
- Add all the metals to acid
- Measure the temperature change of the reaction between the acid and the metal over a set period
- The greater the temperature change the more reactive the metal
Keep the same mass and surface area of metal
