Reactions in Water Flashcards
hydrochloric acid
HCl
Sulfuric acid
H2SO4
nitric acid
HNO3
ethnic acid
CH3COOH
Carbonic acid
H2CO3
phosphoric acid
H3PO4
citric acid
C6H8O7
sodium hydroxide
NaOH
ammonia
NH3
calcium hydroxide
Ca(OH)2
magnesium hydroxide
Mg(OH)2
sodium carbonate
Na2CO3
what is an alkali?
base that is soluble in water. A hydroxide with a group 1 metal.
what are properties of acids?
Sour
Less than 7 pH
Litmus goes red
Corrosive
what are properties of bases?
Bitter pH greater than 7 Litmus goes blue Corrosive Slippery, soapy
what happens when acids and bases react?
neutralise each other (properties disappear).
what are the indicators and what colours do they go?
Litmus
Red with acid
Blue with base
Methyl Orange
Red with acid
Yellow with base
Phenolphthalein
Colourless with acid
Pink with base
what is the bronsted-lowry acids and bases theory? what do acids and bases do?
Acids donate protons.
Bases accept protons.
An acid-reaction involves the transfer of hydrogen from an acid to a base.
what are conjugate acid/base pairs? what is written first? what is an example with water?
Molecules (on different sides of an equation) differ by one proton.
Acid is always written first.
H3O+/H2O
what happens when acid reacts with water?
hydronium ions are produced.
what happens when bases react with water?
hydroxide ions are produced.
what are amphiprotic substances? what is an example?
Capable of both accepting and donating protons.
Water
Can act as an acid or a base.
what defines a strong acid? what are examples? what defines a weak acid? what is used and what are examples?
Strength of an acid is its ability to donate hydrogen ions- ionisation is virtually complete (all acid molecules ionise in water)
Strong acids: HCl, NHO3, H2SO4
A weak acid is an acid for which ionisation is incomplete- formation of ions is limited. Reversible arrows.
Weak acids: ethanoic or acetic acid, carbonic acid and hydrogen carbonate ions.
what defines a strong base? what are examples?
Strong: accept readily
Strong base: oxide, hydroxide.
More soluble metal hydroxides (NaOH and KOH) provide more OH- so are stronger. Alkali bases.
what are mono, di and triprotic acids? how do they react with water?
Monoprotic: have one hydrogen per molecule.
Driprotic: have 2 hydrogens per molecule.
Triprotic: react in 3 stages with water.
what is the difference between strong and weak and concentrated and dilute?
Strong and weak: whether or not the solution completely ionises or dissociates in solution.
Concentrated and dilute: the amount of solute dissolved in a given volume of solution.
what is acidity? how is this measured?
Acidity: concentration of hydrogen ions.
Higher = more acidic
Concentration of acid is measured using pH.
pH scale: less than 7? more than 7? negative? 7?
Less that 7- acidic or more hydronium to hydroxide ions.
More than 7- basic or lower hydronium to hydroxide ions.
Negative- very acidic
7- neutral or equal hydronium to hydroxide ions.
how many decimal places is pH?
1
can hydronium be considered the same as H+?
yes
what happens every time pH changes by one?
concentration changes by factor 10.
Eg. pH 2 is ten times more acidic than pH 3.
how is pH calculated? what is the H3O+ is the equation?
pH = -log [H3O+]
H3O+: represents concentration of the hydronium ion measured in mole per litre
Acid = H3O+ so long as the ionisation is complete. That is, the acid is a strong monoprotic aid.
what formula can be used to find either hydronium or hydroxide, given you have the other?
Kw = [H3O+] x [OH-] = 10^-14
what is used to calculate the hydronium ion concentration in a solution of a given pH? eg?
[H3O+] = 10^-pH
Eg. pH 3.0 means H3O+ = 10^-3 M
what are the concentration formulae?
n = c x V
C1V1 = C2V2
what is a salt?
ionic compound derived from an acid. Usually made of a metal cation and a non-metal anion.
reactions between acids and reactive metals
Reactions between acids and reactive metals
Metals such as Ca, Mg, Zn and group 1
Acid + metal = salt and hydrogen
reactions between acids and metal hydroxides
Example of an acid base reaction
Metal hydroxides: NaOH, Ca(OH)2 and Mg(OH)2
Neutralisation reaction
Acid + hydroxide base = salt + water
reactions between acids and metal oxides
Acid-base
Metal oxides are usually basic
Metal oxides: Na2O, CaO, MgO and ZnO
Oxide base + acid = salt + water
reactions between acids and metal carbonates
Metal carbonates: Na2CO3, CaCO3, MgCO3
Acid + carbonate = salt + water + carbon dioxide
If lime water is added, it will go cloudy with CO2
reactions between acids and metal hydrogen carbonates (bicarbonates)
acid-base, therefore a salt and water
Hydrogen carbonates: NaHCO3, KHOC3 and Ca(HCO3)2
acid + hydrogen carbonate = salt + water + carbon dioxide
what are ionic equations?
what are not separated?
Only involve things that change in states and ionic status etc.
Solids and molecules cannot be separated for these equations.
what are redox equations (reduction and oxidation) in terms of corrosion? equation?
During corrosion, metal combines with oxygen to form metal oxide in a process called oxidation.
When metal is extracted from metal oxide this process is called reduction.
Iron (III) oxide has lost oxygen so it has been reduced.
Carbon monoxide has gained oxygen so it has oxidised.
Fe2O3 (s) + 3CO (g) —-> 2Fe (s) + 3CO2 (g)
what is a redox reaction?
a reaction that involves the transfer of electrons from one chemical to another.
what is oxidation and reduction?
Oxidation: loss of electrons.
Reduction: gain of electrons.
what does oxidation and reduction look like in half equations?
oxidation: has electrons balanced on the right.
Reduction: has electrons balanced on the left.
how are overall redox equations written?
Write two half equations first.
Add them together.
Should not have electrons because electrons produced in oxidation are used in reduction.
what is an oxidant?
Oxidant (oxidising agent): causes another substance to undergo oxidation whilst undergoing reduction itself. Therefore it gains electrons and is reduced.
what is a reductant?
Reductant (reducing agent): causes another substance to undergo reduction while undergoing oxidation itself. Therefore it loses electrons and therefore is oxidised.
what are oxidation numbers?
Determines whether a reaction is redox and identifies the oxidants and reductants.
No physical meaning but keep track of moving electrons.
oxidation numbers: pure elements
Pure element is 0. Eg. Al or O2
oxidation numbers: monatomic ions
charge of ion
oxidation numbers: oxygen- exceptions
Each oxygen in a compound is -2 but not in peroxides and compounds with F.
oxidation numbers: hydrogen in a compound
Hydrogen atoms in compounds is +1 but not in metal hydrides.
oxidation numbers: uncharged molecule
Total oxidation numbers in an uncharged molecule is 0.
oxidation numbers: polyatomic ion
Sum of numbers in a polyatomic ion is the change of the ion.
how are oxidation numbers used?
An increase is called oxidation and species is a reductant.
A decrease is called reduction and species is an oxidant.
how are half equations for complex redox reactions written?
K: balance key elements (not O or H) O: balance oxygen by adding H2O H: balance hydrogen by adding H+ E: balance charges by adding electrons S: states
what are conjugate redox pairs? how are they written? what is an example?
The reductant loses electrons to the oxidant.
Written oxidant/reductant.
Eg. Zn2+/Zn
what is the reactivity series? how are metals ranked? what metals are reactive and not reactive? what are metal cations? what do stronger cations do?
Series ranks metals on their ability to act as reducing agents and oxidise.
Most reactive metals are at the bottom and least reactive are at the top.
A reactive metal wants to lose electrons to become a cation more than a less reactive one.
Group 1 and 2 are most reactive.
Transition metals are less reactive.
Metal cations act as oxidising agents.
Cations higher have greater oxidising strength and undergo reduction.
what does the reactivity series allow you to do? how does this reaction happen?
Order on series allows you to predict which metals will displace metals from solutions of their ions.
More reactive metals will be oxidised by, and donate electrons to, the cation of a less reactive metal.
Cation receives electrons and is reduced.
Oxidant or ion must be higher than the reductant or metal (negative gradient).
what is corrosion?
A redox reaction.
Weakens metal.
what is dry corrosion? what forms? how is this sped up?
Reaction between metal and oxygen.
Makes metal oxide.
Aluminium reacts to form a tough, protective layer that prevents further corrosion.
Moisture makes reaction faster.
what is wet corrosion? what is formed? what conditions are needed? how does it occur?
Rust.
Formation of hydrated oxide of iron (Fe2O3.xH2O).
No protective layer forms but rust that flakes off and allows more water to seep in, causing more corrosion.
Conditions: water, oxygen and impurities.
Presence of water containing an electrolyte (solution can conduct electricity) allows a current.
Iron is one electrode and the impurity (crack etc.) another.
what are the oxidation and reduction equations for wet corrosion?
Fe (s) ——> Fe 2+ (aq) + 2e- (oxidation)
2H2O (l) + O2 (aq) + 4e- ——> 4OH- (aq) (reduction)
how does wet corrosion happen on iron?
Oxidation of iron is due to transfer of electrons through the metal to areas of impurity.
what is the process that follows in wet corrosion?
Iron (II) precipitate with OH- ions to form iron (II) hydroxide, which is oxidised to iron (III) hydroxide.
Fe2+ (aq) + 2OH-(aq) ——> Fe(OH)2 (s)
4Fe(OH)2 (s) + 2H2O (l) + O(aq) ——> 4Fe(OH)3 (s)
how is rust formed?
In air iron (III) hydroxide loses water to form hydrated iron (III) oxide, Fe2O3.xH2O, known as rust.
how do alloys prevent corrosion?
Alloying iron with another metal or carbon increases resistance.
how do protective coatings prevent corrosion?
Most effective.
Completely coat with an impervious substance such as plastic, enamel, paint or grease.
how does impressed current prevent corrosion?
Cathodic protection.
Attach metal to a source of negative change.
Metal receives electrons so oxidation cannot occur.
Metal becomes a site of reduction.
how does sacrificial protection prevent corrosion and what is the equation?
Connect a metal that is lower on the electrochemical series (more reactive).
Metal will react in preference because it oxidises easier.
Complete coating is not needed.
Electrons from metal reaction are used by oxygen and water.
2H2O (l) + O2 (aq) + 4e- ——> 4OH- (aq)
how do unreactive metallic coatings prevent rust?
Less reactive metal coats.
Electroplating.
A break in the coat causes corrosion.
Complete coat is necessary.
