Chemical Changes Flashcards
What are acids
Substances that form hydrogen (H+) ions when they dissolve in aqueous solutions
What are alkalis
Substances that form hydroxide (OH-) ions when they dissolve in aqueous solutions
What is oxidation
Involves gaining oxygen but losing electrons
What is reduction
Involves losing oxygen but gaining electrons
What are examples of the most reactive metals
Potassium,Sodium, lithium, calcium,magnesium,aluminium and carbon
What are examples of the least reactive metals
Zinc, iron, hydrogen, copper, silver, gold and platinum
When can a metal displace another metal
It can only displace another metal from a compound if it’s located above the reactivity series
What is an example of a displacement reaction
Magnesium+iron oxide——> magnesium oxide+ iron
Since magnesium is higher in the reactivity series magnesium atoms have oxidised and the iron atoms have been reduced
How does potassium react against water
Ignites instantly and the metal sets alight
How does sodium react against water
Fizzes rapidly and melts to form a ball that moves around on the water surface
How does lithium react against water
Fizzes steadily and floats
What metals can be extracted from their oxides
Metals that are less reactive than carbon
Why is carbon mainly used for extracting
It’s cheap and abundant
What is the equation of a reaction of a metal with acids
Metal+acid——>salt+hydrogen
What are examples of a reaction of metals with acids
Iron+sulfuric acid—>iron Sulfate+hydrogen
Magnesium+hydrochloric acid—>magnesium chloride+hydrogen
What does a redox reaction involve
Involves a reduction reaction (one reactant gains electrons) and an oxidation reaction (one reactant loses electrons
What is an example of an ionic equation
Magnesium-» Mg2+ + 2e-
Magnesium atom has been oxidised as it has lost electrons
S+2e- —». S2-
The sulfuric atom has been reduced as it has gained electrons
What are acid neutralised by
Acids are neutralised by alkalis and bases to produce salts and water
Acid+ alkali—> salt + water
Acid + bases—> salt + water
Also neutralised by metal carbonates to produce salts, water and carbon dioxide
Acid+ metal carbonate—> salt + water + carbon dioxide
For example
Hydrochloric acid+ copper carbonate makes copper chloride+ water+ carbon dioxide
What do salts contain as a product from the reaction
Contain a positive ion which comes from the base or alkali
Contains a negative ion which comes from the acid
Hydrochloric acid——-» _____ chloride
Sulfuric acid——-» ______ sulfates
Nitric acid ——-»> ______ nitrates
What is the required practical to create blue copper Sulfate crystals
1) start with a fixed volume of dilute sulfuric acid. This is our limiting reactant
2) gently heat the acid with a Bunsen burner until almost boiling
3)Using a spatula add small amounts of copper oxide to the acid
4)stir with a glass rod until the reaction stops (some powder will remain)
Required practical to create blue copper sulphate crystals (2)
5)use filtration to remove the excess insoluble solid
6)Place the solution in an evaporating basin to heat above a beaker of water
7)leave the solution for 24 hours in a cool place for crystallisation to occur
8) scrape the crystals onto a paper towel and gently pat them dry
How can you measure pH
Universal indicator-the indicator changes to a particular colour depending on colour
pH probe-the probe returns a numerical value for a pH of a substance
What happens by every increase of 1 in pH
pH 1 has a 10 x greater concentration of H+ ions than pH 2 so it is in one order of magnitude
pH 1 has an 100x greater concentration of H+ ions that pH 3 so it is in two orders of magnitude
What happens with weak acids
Only partially ionise in aqueous solutions meaning that not all of the acid molecules break up to form H+ ions
You can tell that weak acids are weak from the reversible reaction sign shoeing that some of the molecules ionise but not all
Carbonic acid
Ethanoic acid
Citric acid
What happens with strong acids
Fully ionise in aqueous solutions meaning that all of the acid molecules break up to form a greater concentration of H+ ions
Hydrochloric, sulfuric and nitric acid are strong
What is electrolysis
A process that splits ionic compounds into their different elements
What happens when a voltage is applied on an electrolyte
The charged ions are attracted to the electrode with the opposite charge to the ion
Positive charged ions move to negative electrode (cathode)
Negative charged ions move to the positive electrode (anode)
Ions are discharged at the electrodes producing elements
What is the process of electrolysis in molton compounds
When simple ionic compounds the is electrolysed in the molton state using inert electrodes the metal is produced at the cathode and the non metal is produced at the anode
This is because the metal is the positive ion and the non metal is the negative ion
Why is carbon normally used for extracting metals with electrolysis
It’s a good conductor and it’s cheap
What are the disadvantages to suing electrolysis to extract metal
Lots of energy is needed to melt the solid ionic compounds to allow the ions to flow and produce the current
Energy costs a lot of money
What happens at the anode with electrolysis of aqueous solutions
It depends if halide ions are present. If they are present the halogen forms (bromine fluorine chlorine)!
If halide ions are absent oxygen will form
What happens with the cathode with electrolysis of aqueous solutions
At the cathode it depends on the reactivity of the metal
If the metals more reactive than hydrogen, hydrogen is produced
If the metals less reactive than hydrogen the metal is produces
How do you write half equations
Negative electrode: X+ —> X so ionic equation must be X+ + e- —> X electrons gained so positive ions are reduced
Positive electrode: X- —> X so ionic equation must be X- —> e- + X electrons are lost so negative ions are oxidised
For example 2Br- —> Br2 + 2e-
What is the required practical for electrolysis
1) add about 50cm2 of copper chloride solution to a beaker
2)add the lid and insert electrodes Theo if I the holes making sure the electrodes don’t touch
3)attach crocodile leads to the electrode and connect the rods to the DC terminals of a low voltage power supply
4)Set the power supply ti 4V and switch the power supply on
Required practical for electrolysis
5)using the forceps hold the litmus paper near the positive electrode
6)after a few minutes turn the power supply off and observe the negative electrode
7)record observations at the electrodes
What safety precautions do you need to take
Safety goggles need to be worn
Room should be well ventilated because large quantities of chlorine gas is toxic
What are metal oxides
Metals + oxygen—> metal oxides
This is known as oxidation reactions because the metals gain oxygen
Reduction=loss of oxygen and oxidation =gain of oxygen
In calcium+coppe oxide—> calcium oxide+ copper what has been oxidised and reduced?
Calcium has been oxidised as it has gained oxygen and copper has been reduced as it has lost oxygen
What happens when you react a metal with water
Metal+water-»> metals hydroxide + hydrogen
What can happen when some metals react
They can lose electrons and form a positive ion
The reactivity of a metal depends on ur ability to lose electrons and form a positive ion
The more reactive an element is the higher the ability it has to form a positive ion
How do you write ionic equation
If sodium is oxidised it has lost an electron leaving it with a +1 charge
So Na—» Na+ + e-
If à sodium +1 ion is reduced it has gained an electron leaving it with a charge of 0 so it’ll be
Na+ + e- —> Na
What are examples of redox reactions
2HCl + Mg —> MgCl2 + H2
Mg—> Mg2+ + 2e-
This is oxidation reaction as it loses electrons
2H+ + 2e- —> H2
This is a reduction reaction as it gains electrons
What are the rate of reactions with dilute acids
Magnesium- very rapid reaction so it easily forms Mg2+
Zinc- quite rapid reaction so it quite easily forms Zn2+
Iron- slow reaction so it less easily forms Fe 2+
What is the ionic equation for any neutralisation reaction
H+ + OH- —-> H2O (l)
How does the concentration of acids affect the pH
The concentration of an acid tells us the amount of acid molecules in a given volume of solution
A dilute acid will have fewer acid molecules in a given volume than a concentration acid even if the strength of the acid is the same
How do you extract metals using electrolysis
Metals that are more reactive than Carbon (like aluminium) are too reactive to be extracted by reduction with carbon so they are extracted by electrolysis of molton compounds
Large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current
How is aluminium extracted
Manufactured by the electrolysis of molton mixture of aluminium oxide and cryolite using carbon as the anode
Aluminium oxide has a high melting point so it would be too expensive to melt it which is why it’s mixed with cryolite
The positive electrodes need to be continually replaced because oxygen is formed which reacts with the carbon of positive electrode forming carbon dioxide and they gradually burn away
