Topic 4 Flashcards
What are Metal oxides?
Known as oxidation reactions metals gain oxygen.
Reduction= loss of oxygen & amp; oxidation= gain of oxygen.
What is the reactivity series?
When metals react with other substances, metal atoms form positive ions.
Metals can be arranged in order of their reactivity in a reactivity series.
Non-metals hydrogen and carbon are often included in the reactivity series
A more reactive metal can displace a less reactive metals from a compound (think about how this is similar as well to halogens).
What is extraction of metals and reduction?
Gold, since it is very un-reactive, it is found in the Earth as the metal itself.
But, most metals are found as compounds that require chemical reactions to extract the metal.
Metals less reactive than carbon can be extracted from their oxides by reduction with carbon.
(DON’T FORGET: reduction involves the loss of oxygen)
What is reaction of acids with metals?
These are redox reactions - this means that one substance is reduced and another substance is oxidised.
You should be able to identify which substances are which by looking at electrons gained and lost (following OIL RIG).
What is neutralisation of acids and salt production?
Acids are neutralised by alkalis (e.g soluble metal hydroxides) and bases (e.g insoluble metal hydroxides and metals oxides) to produce salts and water.
Acids are neutralised by metal carbonates to produce salts, water and carbon dioxide.
The salt produced…
1) In alkali and base reactions depends on the acid used…
• Hydrochloric acid produces chlorides(XCl).
• Nitric acid produces nitrates(XNO3).
• Sulphuric acid produces sulphates(XSO4).
2) It also depends on the positive ions in the base, alkali or carbonate i.e. the metal (which is the X in the salts above).
3) Remember: the charges on the positive ions from base/alkali/carbonate and the negative ion from the acid must add up to zero.
What are soluble salts?
They can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates:
1) Add the chosen solid insoluble substance to the acid then the solid will dissolve.
2) You know the acid has been neutralised when excess solid sinks to the bottom, so keep adding until this happens.
3) Filter out excess solid leaving the salt solution, then evaporate some water, then leave the rest to evaporate slowly.
(THIS IS CALLED CRYSTALLISATION.)
What is the pH scale and neutralisation?
Acids produce H+ ions an aqueous solutions.
Alkalis produce OH+ ions in aqueous solutions.
The pH scale (0 to 14) measures the acidity or alkalinity of a solution, and can be measured using universal indicator of a pH probe.
1) pH 7 is neutral
2) pH <7 is acidic
3) pH >7 is alkaline
H(+) + OH- -> H2O is the ionic equation of any neutralisation reaction.
What are Titrations?
The volumes of acid and alkali solutions that react with each other can be measured by titration using a suitable indicator.
How do you carry out a titration?
1) Wash burette using dilute hydrochloric acid and then water.
2) Fill burette to 100cm3 with acid with the meniscus’ base on the 100cm3 line.
3) Use 25cm3 pipette to add 25cm3 of alkali into a conical flask, drawing alkali into the pipette using a pipette filler.
4) Add a few drops of a suitable indicator to the conical flask (eg: phenolphthalein which is pink when alkaline and colourless when acidic).
5) Add acid from burette to alkali until end-point is reached (as shown by indicator).
6) The titre (volume of acid needed to exactly neutralise the acid) is the difference between the first (100cm3) and second readings on the burette.
7) Repeat the experiment to gain more precise results.
What are Titration calculations?
1dm3 = 1000cm3
One mole of a substance in grams the same as its relative atomic mass in grams.
What is the process of electrolysis?
When an ionic substance is melted or dissolved, the ions are free to move about within the liquid or solution.
Passing a current through substances that are molten or solution means that the solution can be broken into elements. This is electrolysis, and the substance being broken down is the electrolyte.
During electrolysis, positively charged ions move to the negatively electrode (cathode), and negatively charged ions move to the positive electrode (anode).
Ions are discharged at the electrodes producing elements.
What is electrolysis of molten ionic compounds?
When a simple ionic compound(e.g. lead bromine) is electrolysed in molten state using inert electrodes, the metal (lead) is produced at the cathode and the non-metal (bromine) is produced at the anode.
This is because the metal is the positive ions and the non-metals is the negative ions.
What is using electrolysis to extract metals?
Metals that are more reactive than carbon (e.g. aluminium), so too reactive to be extracted by reduction with carbon, are extracted by electrolysis of molten compounds.
Large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current.
Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite using carbon as the positive electrode (anode).
1) Aluminium oxide has a very high melting point, so it would be too expensive to melt it, which is why it is mixed with cryolite.
2) The positive electrodes need to be continually replaced because oxygen is formed, which reacts with the carbon of the positive electrodes, forming carbon dioxide, and they gradually burn away.
Metals that react with carbon cab be extracted by electrolysis as well.
What is electrolysis of aqueous solutions?
The ions discharged when an aqueous solution is electrolysed using inert electrodes depend on the relative reactivity of the elements involved.
At the negative electrode (cathode), hydrogen is produced unless the metal is less reactive than hydrogen. This is because more reactive ions want to stay within the solution.
At the positive electrode, if OH- and halide ions are present, then one of the halide ions will be produced. If no halide is present, oxygen is formed.
This happens because in the aqueous solution water molecules break down producing H+ ions and OH- ions that are discharged.
