C4 - Chemical Changes Flashcards
What is the pH scale
A scale going from 1 - 14 which measures how acidic or alkaline a solution is.
The lower the pH of a solution, the more acidic it is
The higher the pH of a solution, the more alkaline it is
A neutral substance (e.g. pure water) is pH 7
Give some examples of these pH scales:
a) pH 1
b) pH 3
c) pH 4
d) pH 5-6
e) pH 7
f) pH 8-9
g) pH 9-10
h) pH 11
i) pH 12-13
j) pH 13-14
a) Car battery acid, stomach acid
b) vinegar, lemon juice
c) acid rain
d) normal rain
e) pure water
f) washing-up liquid
g) pancreatic juice
h) sop powder
i) bleach
j) caustic soda (drain cleaner)
Give 2 ways to measure the pH of a solution
Universal indicator
A pH probe attached to a pH meter
What is an indicator (that measures pH)?
A dye that changes colour depending on the pH. Some indicators contain a mixture of dyes that mean they can gradually change colour over a broad range of pH. These are called wide range indicators and they’re useful for estimating the pH of a solution
acid + base —->
salt + water
It is a neutralisation reaction
(for example, H+ + OH- —> H2O
What do acids and bases combine to make?
A salt + a water, it is a neutralisation reaction
Acids produce what in water?
Protons. They ionise in aqueous - so they produce hydrogen ions (H+), which is just a proton as it has lost its only electron
What is the difference between strong acids and weak acids?
Strong acids ionise completely in water. All acid particles dissociate to release protons
Weak acids do not ionise fully in a solution. Only a small proportion of acid particles dissociate to release H+ ions or protons
The ionisation of a weak acid is a reversible reaction, which sets up an equilibrium reaction.
Give the formulas for the strong acid hydrochloric acd and the weak acid carbonic acid I think ionising in water
Strong = HCl ---> H+ + Cl- Weak = CH3COOH H+ + CH3COO-
Give some examples of
a) Strong acids
b) Weak acids
a) Hydrochloric acid (stomach acid), sulfuric acid, nitric acid
b) Ethanoic acid, citric acid, carbonic acid
Reactions of acids involve H+ ions reacting with other substances. If the concentration of H+ ions is higher, what will happen to the rate of reaction?
It will be faster, so strong acids will be more reactive when ionising in water than weak acids will be when ionising in water
pH is a measure of what?
The concentration of Hydrogen ions
For every decrease of on the pH scale, the concentration of H+ ions increases by a factor 10
What factor does every decrease of 1 on the pH scale mean in terms of hydrogen ions?
For every decrease of on the pH scale, the concentration of H+ ions increases by a factor 10
Strong acids and concentrated acids are concentrated acids. True or false?
False - Acid strength tells you what proportion of acidic molecules ionise in water
Concentrated acids is to do with how much acid is within a certain volume of water. The more acid in a concentrated volume, the more concentrated it is
pH will decrease with increasing acid concentration regardless of whether it’s strong or weak. True or false?
True
Acid + metal oxide —>
Salt + water
Acid + metal hydroxide —>
Salt + water
Will bases that don’t dissolve in water still take part in the neutralisation reaction with acids?
Yes
Some metal oxide and metal hydroxides dissolve in water. These soluble compounds are what?
Alkalis
Acid + metal carbonate —>
Salt + water + carbon dioxide
Hydrochloric acid +
a) copper oxide —>
b) sodium carbonate —>
a) Copper chloride + water
(this follows acid + metal oxide –> salt + water)
b) Sodium chloride + water + carbon dioxide
(this follows acid + metal oxide —> salt + water + CO2)
How can you make soluble salts?
With an insoluble base - you need to choose the right acid and insoluble base, such as an insoluble metal oxide, hydroxide or carbonate. E.g. if you want to make copper chloride, you could mix hydrochloric acid and copper oxide
CuO + HCl —> CuCl2 + H2O
Balance the equation
CuO + 2HCl —> CuCl2 + H2O
Makes a soluble salt with an insoluble base
Rearrange the instructions for the practical of making a soluble salt from an insoluble salt:
1) Then filter out the excess solid to get the salt solution with a funnel and filter paper into a conical flask
2) You need to choose the right acid and insoluble base, such as an insoluble metal oxide, hydroxide or carbonate. E.g. if you want to make copper chloride, you could mix hydrochloric acid and copper oxide
3) To get pure, solid crystals of the salt, gently heat the solution using a water bath or an electric heater to evaporate some of the water (to make it more concentrated) and then stop heating it and leave the solution to cool. Crystals out of the salt should form, which can be filtered out of the solution then dried. This is called crystallisation
4) Gently warm the dilute acid using a Bunsen burner, then turn it off
5) Add the insoluble base a bit at a time, until no more reacts (so the base is in excess). You’ll know when all the acid has been neutralised because, even after stirring, the excess solid will just sink to the bottom without reacting
2) You need to choose the right acid and insoluble base, such as an insoluble metal oxide, hydroxide or carbonate. E.g. if you want to make copper chloride, you could mix hydrochloric acid and copper oxide
4) Gently warm the dilute acid using a Bunsen burner, then turn it off
5) Add the insoluble base a bit at a time, until no more reacts (so the base is in excess). You’ll know when all the acid has been neutralised because, even after stirring, the excess solid will just sink to the bottom without reacting
1) Then filter out the excess solid to get the salt solution with a funnel and filter paper into a conical flask
3) To get pure, solid crystals of the salt, gently heat the solution using a water bath or an electric heater to evaporate some of the water (to make it more concentrated) and then stop heating it and leave the solution to cool. Crystals out of the salt should form, which can be filtered out of the solution then dried. This is called crystallisation
Give the reactivity series from their symbols
K, Na, Li, Ca, Mg, C, Zn, Fe, H, Cu
Potassium Sodium Lithium Calcium Magnesium Carbon Zinc Iron Hydrogen Copper
Give the reactivity series from most - least reactive
Potassium Sodium Lithium Calcium Magnesium Carbon Zinc Iron Hydrogen Copper
For metals, how is their reactivity measured?
How easily they lose electrons, forming positive ions The higher up the reactivity series a metal is, the mroe easily they form positive ions Potassium Sodium Lithium Calcium Magnesium Carbon Zinc Iron Hydrogen Copper
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Potassium Sodium Lithium Calcium Magnesium Carbon Zinc Iron Hydrogen Copper
Acid + metal —>
Salt + Hydrogen
When a metal reacts with water or acid, what happens? What does this have to do with their reactivity?
They lose electrons and become positive ions.
So, the higher a metal is on the reactivity series, the more easily it reacts with water or acid
Acid +
a) metal —>
b) base —>
c) metal oxide —>
d) metal hydroxide —>
e) metal carbonate —>
f) water —>
a) Salt + hydrogen
b) Salt + water
c) Salt + water
d) Salt + water
e) Salt + water + carbon dioxide
f) Metal hydroxide + hydrogen
The speed of the reaction with acid + metal is indicated by what?
How quickly the hydrogen bubbles are given off
acid + metal —> salt + hydrogen
The more reactive a metal, the faster the reaction will go. Very reactive metals react explosively, but less reactive metals react less violently. In general, copper won’t react with cold, dilute acids
How was the reactivity series made?
By comparing the relative reactivity of different metals in either an acid or water and put them in order from most to least reactive
How else can you investigate the reactivity of metals?
By measuring the temperature change of the reaction with an acid or water over a set period of time. If you use the same mass and surface area of metal each time, then the more reactive metal, the greater the temperature change
Metal + water —>
Metal hydroxide + water
This is used to show the reactivity of metals
Which out of these metals will react with water?
a) Potassium
b) Copper
c) Iron
d) Lithium
e) Zinc
f) Sodium
g) Calcium
a) Potassium
f) Sodium
d) Lithium
g) Calcium
Which elements in the reactivity series can be extracted using electrolysis?
The first 5 - Potassium, Sodium, Lithium, Calcium, Magnesium
They are more reactive than carbon, so trying to separate it using reduction by carbon wouldn’t work, as the oxygen would stay with the most reactive element - these
ELECTROLYSIS IS EXPENSIVE
Which elements on the reactivity series can be extracted using reduction by carbon and why?
The last 3 - Zinc, iron and copper
Because carbon can only take the oxygen away (reduce) from metals which are less reactive than carbon itself
Why are some metals found as ores?
They are so unreactive, they’re just in the earth as itself. E.g. gold
What is a redox reaction?
If electrons are transferred - A loss of electrons is called oxidation. A gain of electrons is called reduction. As reduction and oxidation happen at the same time, it is a REDOX reaction
OILRIG means what?
Oxidation Is Loss (of electrons)
Reduction Is Gain (of electrons)
Give an example of a redox reaction
Displacement reactions - one metal kicking the other out of a compound
A MORE REACTIVE METAL WILL
DISPLACE A LESS REACTIVE ONE
this is a type of redox reaction
Iron + copper sulfate —> iron sulfate + copper
Fe + CuSO4 —————> FeSO4 + Cu
Which is oxidised, which is reduced?
Fe —> Fe2+ + 2e-
Cu2+ + 2e- —> Cu
In this reaction, the iron loses 2 electrons to become a 2+ ion - it’s oxidised
The copper ion gains these 2 electrons to become a copper atom - it’s reduced
In displacement reaction, it’s always the metal ion that gains electrons and is reduced. The metal atom always loses electrons and is oxidised. True or false?
True
What do ionic equations show?
Equations only concentrating on the parts of the reaction that are reduced or oxidised
What is the definition of electrolysis?
Splitting up with electricity
What is an electrolyte?
A liquid or solution that can conduct electricity.
What is an electrode?
A solid that conducts electricity and is submerged in the electrolyte
During electrolyisis, what happens?
An electric current is passed through an electrolyte (a molten or dissolved ionic compound). The ions move towards the electrodes, where they react, and the compound decomposes
Where will these different ions go to in electrolysis?
a) The positive ions
b) The negative ions
a) The cathode (-ve electrode) and gain electrons. THEY ARE REDUCED
b) The anode ( +ve electrode) and lose electrons. THEY ARE OXIDISED
The positive ions go to the cathode, gain electrons so oxidised. True or false?
False - they are REDUCED
The movement of ions to where they go creates what?
A flow of charge through the electrolyte as ions travel to the electrodes
As ions gain or lose electrons, they form uncharged elements and are discharged from the electrolyte
Electrolysis of molten ionic solids forms what?
Elements
Why can’t an ionic solid be electrolysed? How do you solve this?
Because the ions are in fixed position an cannot move.
So, they are molten as then their ions can move freely and conduct electricity
Positive metal ions are what at the cathode?
They are reduced - they gain electrons
Negative non-metal ions are what at the anode?
They are oxidised - they lose electrons
With lead:
Pb 2+ + 2e- —> Pb
Which electrode does this half equation belong to?
The cathode, because lead is a metal, so will form a positive ion as they are reduced and gain electrons at the cathode
Also because the cathode/ negative electrode half equations are always structured that way, + = normal
With Bromine:
2Br- —> Br2 + 2e-
Which electrode does this half equation belong to?
The anode, because bromin is a non-metal, so will form a negative ion as they oxidised and lose electrons at the anode
Also because the anode/ positive electrode half equations are always structured normal = _ + _
Metals can be extracted from their ores using what?
Electrolysis
If a metal is too reactive to be reduced with carbon or it does react with carbon, then electrolysis can be used to extract it. IT’S EXPENSIVE WITH ENERGY COSTS
Aluminium is extracted from what ore and how?
The ore bauxite by electrolysis. Bauxite contains aluminium oxide
2Al2O3 —> 4Al + 3O2
Write the half equations at each electrode for the breakdown of aluminium oxide from the ore bauxite
Negative electrode, there’s reduction - gain of electrons:
Al3+ + 3e- —> Al
Positive electrde, there’s oxidation - loss of electrons
2O2- —> O2 + 4e-
It may be easier to discharge ions from water than from what?
The solute
If H+ ions and metal ions are present , hydrogen gas will be produced at which electrode?
The cathode (negative electrode)
If OH- and halide ions are present, molecules of chlorine, bromine or iodine will be formed. If no halide ions are present, what happens?
The OH- ions are discharged and oxygen is formed
Fill the blanks:
At the _______, if H+ and _____ ion are present, hydrogen gas will be produced if the metal ions form an elemental metal ____ reactive than hydrogen. If those ions form an elemental that is ___ reactive than hydrogen, then a solid layer of pure metal will be produced instead.
Cathode
Metal
More (e.g. sodium ions)
Less (e.g. copper ions)
Fill the blanks:
At the _____, if OH- and ______ ions are present, molecules of chloring, bromine or iodine will be formed. If none of those ions are present, then the OH- ions will be __________ and oxygen will be formed
Anode
Halide (group 7)
Discharged
What is the test for:
a) Oxygen
b) Hydrogen
c) Chlorine
d) Carbon dioxide
a) Relights a glowing splint
b) Makes a “squeaky pop” with a glowing splint
c) Bleaches damp litmus paper, turning it white
d) Turns lime water cloudy
When a halide isn’t present in the aqueous solution, the half equation for the anode is what?
4 OH- –> O2 + 2 H2O + 4 e-
or
4 OH- -4e- —> O2 + 2 H2O
