C4- Chemical Changes Flashcards
The lower the pH of a solution, the more _ it is
Acidic
The higher the pH of a solution, the more _ it is
Alkaline
What pH does a neutral substance have
7
What are the 2 way to measure pH
Using an indicator or a pH probe attached to a pH meter
What do acids and bases do
Neutralise each other
Acid + base →
Salt + water
H^+(aq) + OH^-(aq) →
H2O(l)
What are the 5 steps of the titration practical
- Using a pipette and pipette filler, add a set volume of the alkali to a conical flask.Add two or three drops of indicator too
- Use a funnel to fill a burette with some acid of known concentration. Make sure you do this BELOW EYE LEVEL- you don’t want to be looking up if some acid spills over. (Wear safety goggles) Record the initial volume of the acid in the bruette
- Using the burette, add the acid to the alkali a bit at a time- giving the conical flask a regular swirl. Go especially slowly when you think the end-point (colour change) is about to be reached
- The indicator changes colour when all the alkali has been neutralised, e.g phenolphthalein is pink in alkaline conditions, but colourless in acidic conditions
- Record the final volume on acid in the burette, and use it, along with the initial reading, to calculate the volume of acid used to neutralise the alkali
You need to repeat the titration experiment until your answers are within _cm^3 of each other
0.1
What colour do alkalis go when using litmus
Blue
What colour do alkalis go when using phenolphthalein
Pink
What colour do alkalis go when using methyl orange
yellow
What colour do acids go when using litmus
Red
What colour do acids go when using phenolphthealein
Colourless
What colour do acids go when using methyl orange
Red
HCI →
H^ +CI^-
HNO3→
H^+ + NO^-3
Strong acid: HCI→
H+ + CL-
Weak acid:CH3COOH →
H+ _ CH3COO-
pH is a measure of the concentration of _ _
Hydrogen ions
Factor H+ ion concentration changes by=
10^-x
Name three bases
Metal oxides ,metal hydroxides and metal carbonates
Acid + Metal Oxide →
Salt + Water
Acid + Metal Hydroxide →
Salt + Water
What do acids and metal carbonates produce
Carbon dioxide
List the reactivity series
Potassium Sodium Lithium Calcium Magnesium Carbon Zinc Iron Hydrogen Copper
Acid + Metal →
Salt + Hydrogen
Metal +Water →
Metal hydroxide + Hydrogen
What does oxidation mean
Gain of oxygen
What does reduction mean
Loss of oxygen
What Metals would be extracted by using electrolysis
Potassium Sodium Lithium Calcium Magnesium
What Metals would be extracted by reduction using carbon
Zinc
Iron
Copper
What does OIL RIG stand for
Oxidation Is Loss Reduction Is Gain
Are displacement reactions redox reactions
Yes
Electrolysis means…
Splitting up with electricity
Why are some elements extracted using electrolysis
They are more reactive than carbon
Are metals attracted to negative or positive electrodes
Negative
Are non-metals attracted to negative or positive electrodes
Positive
What is an aqueous solution
A solution in which the solvent is water.
What is a covalent bond
Covalent bonding results in the formation of molecules or giant structures.
How many covalent bonds do hydrogen atoms make
One
What is oxidation/reduction?
Oxidation - When a substance gains oxygen
Reducation - When a substance loses oxygen
What is the reactivity series of
metals? What are the trends in
reactivities of metals in reactions
with acids/water?
The series shows the metals in order of their reactivity.
Metals above H2
in reactivity series react with acid to produce H2
. The more
reactive the metal is, the quicker and more violent reaction with acid occurs.
Metals below H2
don’t react with acids.
Not all metals above H2
react with water - mostly Group I and II metals. Aluminium
What is a displacement reaction?
A reaction where a more reactive metal displaces a less reactive metal from a
compound
How are unreactive metals found in Earth?
In their natural state (well, they are unreactive…)
How can metals less
reactive than carbon be
extracted?
Reduction with carbon. Carbon displaces the metal in a metal oxide - gets
oxidised to carbon oxides. Metal from the metal oxide gets reduced to the pure
metal.
How are metals more reactive than carbon extracted?
By electrolysis
How are oxidation and reduction defined in terms of electron
transfer?
Oxidation – loss of electrons
Reduction – gain of electrons
What is the general equation for a
reaction between metals and
acids? What type of reaction is
this?
Metal + acid → salt + hydrogen
Redox reaction, also a displacement reaction
Which metals in the reactivity series will react with acid?
Those above hydrogen
What is the general equation for a
neutralisation reaction?
Base + acid → salt + water
What is the general equation for
the reaction between metal
carbonate and acid?
Metal carbonate + acid → salt + water + carbon dioxide
What is the general equation for the reaction between metal
carbonates and acids?
Metal carbonate + acid → salt + water + carbon dioxide
What is a redox reaction?
A reaction where both oxidation and reduction occurs
Explain in terms of gain or loss of electrons which species has been oxidised and which species has been reduced when magnesium reacts with hydrochloric acid
Magnesium has lost electrons and thus has been oxidised (Mg to Mg2+)
The hydrogen in HCl has gained electrons and thus has been reduced (H+ to H2)
How is a soluble salt formed?
a) React the excess acid with some insoluble chemical (e.g. metal oxide)
b) Filter off the leftovers
c) Crystallise the product
What do acids and alkalis produce in aqueous solutions?
Acids produce hydrogen ions, alkalis produce hydroxide ions
What are bases, acids and
alkalis?
Bases are compounds that neutralise acids, acids produce hydrogen ions in
aqueous solutions, alkalis are soluble bases - produce hydroxide ions in aqueous
solutions
What is the pH scale and what
does a pH of 7 show
The measure of acidity/alkalinity of a solution; neutral solution
State the general equation for a neutralisation
reaction in a short, ionic form.
H+ + OH− → H2O
What is a strong acid? What is
a weak acid?
Strong acid is completely ionised in aqueous solution; weak acid is only partially
ionised in aqueous solution
What happens to pH as
concentration of H+
increases?
The pH decreases
What is a concentrated acid and
what is a dilute acid? Is this the
same as a strong and weak acid?
- Concentrated acid has more moles of acid per unit volume than dilute (dilute
refers to solutions of low concentrations) - It is not the same - concentration is not the same thing as strength of an acid.
- Strength refers to whether the acid is completely ionised in water (strong) or
only partially (weak)
As the pH is decreased by one
unit, what change is seen in the
hydrogen ion concentration?
Increases by a factor of 10
Name the following salts: LiNO3 , K2CO3 , MgBr2 , BaSO4
Lithium nitrate
Potassium carbonate
Magnesium bromide
Barium sulfate
What is electrolysis
The passing of an electric current through ionic substances that are molten or in
solution to break them down into elements; ions are discharged (they lose/gain
electrons) at electrodes to produce these
What is an electrolyte?
The liquid/solution which conducts electricity
What is a cathode and what is
an anode
Cathode is the negative electrode, anode is the positive electrode
What occurs at the cathode
and what occurs at the anode
during electrolysis?
Reduction occurs at the cathode
Oxidation occurs at the anode
In aqueous electrolysis, which
element is discharged at the
cathode? Oxygen is produced at
the anode unless what?
The less reactive element discharges at the cathode. Hydrogen is produced unless
there is a less reactive metal, in which case the said metal is produced. Oxygen is
produced at the anode unless the solution contains halide ions, in which case
halogen molecules are produced.
How is aluminium manufactured?
Why is it expensive?
Aluminium is made through the electrolysis of aluminium oxide and cryolite.
Lots of energy is needed to produce the current in electrolysis which makes this
process expensive.
What are the half equations in
the extraction of aluminium?
Al3+ + 3 e− → Al (cathode)
2 O2− → O2 + 4 e− (anode)
Oxygen reacts with C of the anode producing CO2
.
Why is cryolite used in this
process?
It lowers the melting point of aluminium oxide, reducing energy costs
What are the half equations in electrolysis of the aqueous
Na2SO4?
2 H+ + 2 e−→ H2 (cathode) 4 OH− → 2 H2O + O2 + 4 e-(anode)
What are the half equations in
electrolysis of the molten and
aqueous KCl?
K+ + e− → K (cathode) 2 Cl−→ Cl2 + 2 e− (anode) 2 H+ + 2 e− → H2 (cathode) 2 O2− → O2+ 4 e− (anode), respectively
What are the half equations in
electrolysis of the aqueous
CuBr2?
Cu2+ + 2 e− → Cu (cathode)
2 Br−→ Br2 + 2 e− (anode)
