Topic 3.1-3.21 Acids

Hydrogen ions

Hydroxide ions

A neutral solution has a pH of 7 and that acidic solutions have lower pH values and alkaline solutions higher pH values

Alkalis turn pink Acids are colourless

Alkalis turn yellow Acids are red

Alkalis turn blue Acids turn red (Same for blue/red litmus paper. Red litmus paper stays red in acid, turns blue in alkali. Blue litmus paper turns red in acid, stays blue in alkali)

The higher the concentration of hydrogen ions in an acidic solution, the lower the pH. The higher the concentration of hydroxide ions in an alkaline solution, the higher the pH.

As hydrogen ion concentration in a solution increases by a factor of 10, the pH of the solution decreases by 1 unit.

​ ​​​​​​​​​​​Concentrated​ ​=​ ​larger​ ​quantity​ ​of​ ​solute​ ​in​ ​a​ ​given​ ​volume​ ​of​ ​a​ ​solution Dilute​ ​=​ ​smaller​ ​quantity​ ​of​ ​solute​ ​in​ ​a​ ​given​ ​volume​ ​of​ ​a​ ​solution

-Add​ ​dilute​ ​HCl​ ​to​ ​the​ ​beaker​ ​and​ ​measure​ ​pH -Add​ ​weighed​ ​mass​ ​of​ ​calcium​ ​hydroxide​ ​and​ ​stir​ ​then​ ​record​ ​pH -Keep​ ​adding​ ​weighed​ ​masses​ ​of​ ​calcium​ ​hydroxide​ ​until​ ​there​ ​is​ ​no​ ​more change​ ​to​ ​the​ ​pH To analyse it: -draw​ ​a​ ​line​ ​graph​ ​with​ ​mass​ ​added​ ​on​ ​the​ ​horizontal​ ​axis​ ​and​ ​with​ ​pH​ ​on the​ ​vertical​ ​axis -draw​ ​a​ ​line​ ​of​ ​best​ ​fit​ ​(remember​ ​to​ ​ignore​ ​any​ ​anomalies)

Strong​ ​acid​ ​=​ ​fully​ ​dissociates​ ​in​ ​aqueous​ ​solution​ ​(dissociation​ ​is​ ​where​ ​an​ ​acid breaks​ ​down​ ​to​ ​release​ ​H​+​​ ​ions​ ​in​ ​solution) Weak​ ​acid​ ​=​ ​partially​ ​dissociates​ ​in​ ​aqueous​ ​solution as it has fewer H+ ions than expected Stronger​ ​an​ ​acid,​ ​greater​ ​the​ ​dissociation,​ ​the​ ​more​ ​H​+​​ ​ions​ ​released,​ ​the​ ​lower the​ ​pH​ ​(for​ ​a​ ​given​ ​conc.​ ​of​ ​aq.​ ​solutions)

A base is any substance that reacts with an acid to form a salt and water only

A soluble base

A salt + hydrogen gas (H2)

A salt + water (Metal​ ​hydroxides​ ​are​ ​bases/alkalis​ ​if​ ​insoluble/soluble)

A salt + water (Metal​ ​oxides​ ​are​ ​normally​ ​bases​ ​(because​ ​insoluble))

A salt + water + carbon dioxide

Use a burning split held at the open end of a test tube of the gas. If it contains hydrogen it creates a ‘squeaky pop’ sound

Bubble​ ​the​ ​gas​ ​through​ ​the​ ​limewater​ ​(calcium​ ​hydroxide​ ​solution)​ ​and​ ​it will​ ​turn cloudy/output a white precipitate if it contains carbon dioxide

​A reaction​ ​between​ ​an​ ​acid​ ​and​ ​a base

A reaction in which hydrogen ions (H+) from the acid react with hydroxide ions (OH–) from the alkali to form water H​+(​aq)​​+​​OH​-(​aq)​​->​​H2​O​(l)

-Add excess​ ​of​ ​the​ ​reactant * this​ ​is​ ​to​ ​ensure​ ​your​ ​volume​ ​of​ ​acid​ ​reacts​ ​completely -Remove excess​ ​reactant * this​ ​is​ ​done​ ​by​ ​filtration​ ​of​ ​the​ ​insoluble​ ​reactant​ ​and​ ​is​ ​done​ ​so​ ​that​ ​you are​ ​left​ ​with​ ​just​ ​a​ ​salt​ ​and​ ​water -The​ ​remaining​ ​solution​ ​is​ ​only​ ​salt​ ​and​ ​water * this​ ​is​ ​because​ ​all​ ​of​ ​your​ ​acid​ ​has​ ​fully​ ​reacted​ ​and​ ​you​ ​have​ ​filtered​ ​off your​ ​other​ ​reactant,​ ​so​ ​that​ ​the​ ​only​ ​products​ ​of​ ​your​ ​reaction​ ​are​ ​a​ ​salt and​ ​water * if​ ​you​ ​have​ ​used​ ​a​ ​carbonate​ ​you​ ​would​ ​still​ ​only​ ​have​ ​a​ ​salt​ ​and​ ​water remaining​ ​as​ ​carbon​ ​dioxide​ ​gas​ ​would​ ​have​ ​been​ ​given​ ​off​ ​into​ ​the atmosphere

-Titration​ ​must​ ​be​ ​used: * both​ ​reactants​ ​are​ ​liquids/soluble,​ ​so​ ​if​ ​you​ ​have​ ​an​ ​excess​ ​of​ ​one​ ​you would​ ​not​ ​be​ ​able​ ​to​ ​easily​ ​remove​ ​it​ ​from​ ​your​ ​mixture​ ​of​ ​products,​ ​this means​ ​you​ ​need​ ​to​ ​measure​ ​the​ ​exact​ ​amount​ ​of​ ​volumes​ ​that​ ​react, which​ ​is​ ​easily​ ​done​ ​using​ ​a​ ​titration. -You​ ​can​ ​then​ ​mix​ ​the​ ​exact​ ​proportions​ ​of​ ​the​ ​two​ ​reactants -The​ ​exact​ ​amount​ ​of​ ​acid​ ​has​ ​thus​ ​been​ ​added​ ​to​ ​the​ ​soluble​ ​reactant,​ ​meaning that​ ​the​ ​leftover​ ​solution​ ​is​ ​only​ ​salt​ ​and​ ​water,​ ​no​ ​acid​ ​or​ ​alkali,​ ​because​ ​they have​ ​been​ ​completely​ ​neutralised

-Add​ ​an​ ​excess​ ​of​ ​copper​ ​oxide​ ​(insoluble)​ ​to​ ​your​ ​acid​ ​(sulfuric​ ​acid — H​2S​O​4 — as​ ​you​​ are​​ making​​ copper​​ SULFATE) -use​ ​a​ ​filter​ ​and​ ​filter​ ​paper​ ​to​ ​filter​ ​off​ ​any​ ​copper​ ​oxide​ ​that​ ​hasn’t reacted​ ​(your​ ​solution​ ​should​ ​be​ ​blue​ ​as​ ​copper​ ​sulfate​ ​solution​ ​has​ ​been formed) -evaporate​ ​off​ ​the​ ​water​ ​by​ ​placing​ ​your​ ​final​ ​solution​ ​in​ ​a​ ​water​ ​bath