Acids + Electrolysis Flashcards
What ions make aqueous solutions acidic?
Hydrogen ions (H+)
Which ions make aqueous solutions alkaline?
Hydroxide ions (OH-)
What is the pH scale?
The pH scale ranges from pH 0 to pH 14 and measured the acidity and alkalinity of a solution
What can be used to measure pH
Universal indicator
ph Probe
What colour is phenolphthalein in acid and alkali and neutral?
Acid - colourless
Alkali - Pink
Neutral - colourless
What colour is methyl orange in acid and an alkali and neutral?
Acid - red
Alkali - yellow
Neutral - yellow
What colour is blue litmus paper is an acid and alkali?
Acid - turns red
Alkali - stays blue
What colour is red litmus paper in acid and alkali
Acid - stays red
Alkali - turns blue
Suggest a problem with using universal indicator to test the pH of a solution
The colour of the solution is matched to a pH colour chart. This is quite subjective as people may disagree with which colour the solution matches.
It doesn’t provide an exact pH value.
If pH decreased by one unit, what happens to the concentration hydrogen ions concentration
H+ conc Increases by a factor of 10
What is a neutralisation reaction? During an acid-alkali neutralisation reaction, what happens?
A neutralisation reaction is a reaction between an acid and a base.
In an acid-alkali neutralisation, H+ ions from the acid react with OH- ions from the alkali to form water.
What is ionic equation for a neutralisation reaction?
What do the terms concentrated and dilute mean when talking about acid? Is this the same as strong/weak acids?
Concentrated acids have more moles of acid per unit volume of water than dilute acids
Strength refers to whether the acid has completely dissociates in water or not.
An acid that only partially dissociates into H+ ions in water …
Is a weak acid
A base is..
Any substances that reacts with an acid to form salt and water only
Alkalis are..
Soluble bases.
Metal + acid —>
Salt + hydrogen
Metal oxide + acid
Salt + water
Acid + metal hydroxide —>
Salt + water
Acid + metal carbonate
Salt + water + carbon dioxide
Why are metal oxides normally based rather than alkalis?
Metal oxide are normally insoluble
Alkalis are soluble
Describe chemical test for hydrogen
Insert a lit splint into a test tube gas
Hydrogen will burn and a “squeaky pop” will be heard if hydrogen is present.
Describe chemical test for carbon dioxide?
Bubble the gas through limewater (calcium hydroxide)
Limewater turns cloudy if carbon dioxide is present
When a soluble salt is prepared from an acid and an insoluble reactant, why is excess of the insoluble reactant added?
To ensure all the acid reacts
When a soluble salt is prepared from an acid an an insoluble reactant, how and why is excess reactant removed?
By filtration
It is removed to leave a pure solution of the salt
What method must be used to prepare a salt from an acid and a soluble reactant?
Titration
Describe how to carry out an acid-alkali titration
What 3 steps are required when producing a pure dry salt from an acid and alkali?
Complete a titration to find volume of acid that reacts exactly with a set volume of alkali
Use the results from titration to mix the acid and alkali in the correct proportions.
Evaporate the water from the solution,leaving pure dry salt crystals
Most common chlorides are soluble. What are two exceptions?
Silver chloride and lead chloride are insoluble.
Are nitrates soluble or insoluble?
Soluble
All common sodium, potassium and ammonium salts are..
Soluble
Most common sulfates are soluble expect ?
Lead sulfate, calcium sulfate and barium sulfate which are insoluble
Most common carbonates and hydroxide are insoluble. What are the three exceptions?
The carbonate/hydroxides of sodium, potassium and ammonium are soluble
What salt is produced when lead reacts with sulfuric acid? Will a precipitate form?
Lead sulfate
A precipitate will form because lead sulfate in insoluble
What is an electrolyte?
An ionic compound in its molten or aqueous state.
Aqueous - dissolved in water
Why can an electrolyte carry charge?
An ionic compound in is molten or aqueous state has mobile ions which can carry charge.
What is electrolysis?
A process which uses electricity (direct current) to decompose electrolytes.
What is cathode and anode?
Cathode - negative electrode anode - positive electrode
Where do charged ions in the electrolyte move to during electrolysis?
Cations move towards the cathode
Anions move towards the anode
What happens at the anode during electrolysis?
The anions (negatively charged ions) lose electrons to form their elements. Oxidation happens
What happens at the cathode during electrolysis?
Cations (positively charged ions) gain electrons to form their elements
Reduction happens
Name the processes that occur at each electrode during electrolysis?
Anode - oxidation
Cathode - reduction
What is formed at each electrode in electrolysis?
Cathode:metal or hydrogen
Anode: non metal
How can you predict whether a metal or hydrogen will form at the cathode?
If hydrogen is above the metal in the reactivity series then the metal will form.
If the metal is more reactive than hydrogen,then hydrogen will form.
What are the half equations at the cathode and anode during electrolysis of copper chloride?
What is oxidation in terms of electrons
Loss of electrons
What is reduction in terms of electrons
Gain of electrons
