Section 3 - Cemical Changes Flashcards
What is the pH scale?
A measure of how alkaline or acidic a solution is.
Where are acids on the pH scale?
Below 7.
Where are alkalis on the pH scale?
Above 7.
What is a base?
A substance that reacts with an acid to make a salt.
What is an acid?
A substance that reacts with base to make a salt.
What is an alkali?
A base that is soluble in water.
How can pH be measured?
Using indicators or electronic testing devices.
How does the concentration of hydrogen change through the pH scale?
The lower the pH the higher the concentration of hydrogen.
Where is neutral on the pH scale?
7
What is an Indicator?
A dye that changes colour due to pH.
What colours does universal indicator become? At what pHs?
Reds in acidic solutions, green when neutral and purple when alkaline.
What colours does litmus become? At what pHs?
Red in acids, purple when neutral and blue when alkaline.
What colours does methyl orange become? At what pHs?
Red in acids and yellow when neutral.
What colours does phenolphthalein become? At what pHs?
Colourless and clear in acidic or neutral solutions but pink in alkalis.
What is the reaction between an acid and a base called?
Neutralisation.
Where do neutralisation reactions occur?
In aqueous solutions.
What are the products of neutralisation? What pHs are they?
Salts and water, both are a pH of 7.
What do all acids do in water?
Ionise, or dissociate, forming a hydrogen ion and another ion.
What does an acid’s strength mean?
What proportion of the acid molecules ionise in water.
If an acid is weak, what does it mean?
A small proportion of the acid molecules ionise in water.
If an acid is strong, what does it mean?
A large proportion of the acid molecules ionise in water.
What type of reaction is the ionisation of a weak acid? What does this form?
The reaction is reversible, this creates an equilibrium.
What is concentration in acids?
The amount of acid per litre.
How does an acids concentration effects its pH?
If the concentration of hydrogen ions changes by a factor of ten, the pH changes by one inversely.
What happens when a metal reacts with an acid?
It produces salt and hydrogen.
What happens when a metal carbonate reacts with an acid?
It produces salt, water and carbon dioxide.
How can carbon dioxide be tested for using limewater?
The limewater changes colour from clear to cloudy yellow when carbon dioxide is bubbled through it.
Are common chlorides soluble?
Yes, except silver chloride and lead chloride.
Are common sulfates soluble?
Yes, except lead, barium and calcium sulfate.
Are common carbonates and hydroxides soluble?
No, except those of sodium, potassium and ammonium.
Are common salts of sodium potassium and ammonium soluble.
Yes.
Are nitrates soluble?
Yes.
How are insoluble salts made?
Precipitation reactions.
What is electrolysis?
The breaking down of a substance using electricity.
What is oxidation?`
The loss of electrons in a reaction.
What is a reduction reaction?
Gaining electrons in a reaction.
How does electrolysis work?
By passing an electric current through a electrolyte, causing it to decompose.
What is an electrolyte?
A molten or dissolved ionic compound.
What makes up an electrochemical cell?
A cathode, anode, d.c power supply and an electrolyte.
In electrolysis, what happens to the ions?
They head to either electrode depending on charge.
In electrolysis, where do positive ions head?
Towards the cathode.
In electrolysis, where do negative ions head?
Towards the anode.
In electrolysis of an aqueous solution, how could hydrogen gas form?
Provided hydrogen ions are present and the metal is more reactive than hydrogen then hydrogen gas begins to form at the cathode.
In electrolysis of an aqueous solution, how could oxygen be formed?
Provided no halide ions are present then oxygen will form at the anode.
