Chapter 8/ 18 Flashcards

Question

pH scale

Answer 1

- an inverse scale - higher the conc. of H+ ions in solution, lower pH value - lower the conc. of H+ ions, higher the pH value - scale is logarithmic to base 10 (change of 1 pH unit corresponds to 10x change in Hydrogen ion conc.)

Answer 2

- higher conc. of OH- ions = higher pH value | - lower conc. of OH- = lower pH value

Answer 3

Water - [H+] = [OH-] - pH = 7 - neutral solution Acid solution: - [H+] > [OH-] - pH lower than 7 - litmus turns red Basic solution: - [OH-] > [H+] - pH higher than 7 - litmus turns blue

Answer 4

``` pH = -log [H+(aq)] [H+] = 10^-pH ```

Answer 5

pOH = -log[OH-]

Answer 6

A weak acid or a weak base in which the dissociated and undissociated forms have different colours - depending on conc. of H+/OH- ions in solution, one colour or the other is shown

Answer 7

- a common indicator (can't be used to determine a pH value for a solution) - a qualitative indicator - made from a natural source, lichens - in acidic solutions, litmus appears red - in alkaline solutions, litmus appears blue

Answer 8

Acid: red Alkali: yellow

Answer 9

Acid: colourless Alkali: pink/purple

Answer 10

A mixture of indicators that produces different colours in solutions of different pH - pH of aqueous solutions can be measured using universal indicator as either a solution or in paper form

Answer 11

May be used to measure pH of a solution | - makes use of the fact that their colour changes w/ pH

Answer 12

Produces a more accurate method of measuring pH, provided they're correctly calibrated - electrode of pH meter is placed in solution to be tested - a voltage is generated that's converted into a pH meter reading displayed on the screen - pH meter is calibrated using buffers of known pH, usually of pH 4.0, 7.0 and 10.0

Answer 13

Pure water is a v. poor conductor of electricity - means it must have a low conc. of mobile ions responsible for electrical conductivity of solutions - water molecules do dissociate (or ionise) to a v. small extent - conc. of water is constant

Answer 14

Kw = [H+][OH-] - Kw is temp. dependent - so, at a certain temp., product of [H+] and [OH-] is a constant - so, as [H+] of a solution increases, [OH-] decreases - neutral solution has a [H+] = [OH-]

Answer 15

For a strong acid or base, [H+] or [OH-] is equal to its conc. - because strong acids and bases are completely ionised in solution

Answer 16

Acids and bases can be classified as strong or weak - strength of an acid/ base refers to its degree of dissociation in aqueous solutions - strong acids and bases completely dissociate in solution - weak acids and bases only partially dissociate in solution

Answer 17

Means to break apart an ionic compound into its constituent ions

Answer 18

Have a high concentration, measured in mol/dm^3

Answer 19

When a strong acid dissolves in water, it completely dissociates into ions - all molecules of acid react w/ water to produce hydronium (H3O+) or hydrogen (H+) ions HA (g or l) --> H+ (aq) + A- (aq) Can also be written involving formation of hydronium ion (H3O+) HA (g or l) + H2O (l) --> H3O+ (aq) + A- (aq) - position of equilibrium lies to the right, means that strong acid completely dissociates into its constituent ions - solution of a strong acid contains virtually no undissociated HA molecules - conc. of H3O+ ions in solution = initial conc. of strong acid NB/ for a strong acid, conc. of H+ ions = initial conc. of strong acid

Answer 20

- weak acids - when water is added, only a small % of its molecules dissociate to form H3O+ ions - an equilibrium is established, where majority of acid molecules don't dissociate into ions - position of equilibrium lies to left

Answer 21

HA (aq) H+(aq) + A-(aq) Can also be written as: HA(aq) +H2O (l) H3O+(aq) + A-(aq)

Answer 22

One which completely dissociates into ions in aqueous solution - strong bases include metal hydroxides of group 1 General equation: MOH(aq) --> M+(aq) + OH-(aq) - position of equilibrium for dissociation of a strong base lies to the right Conc. of OH- ions = initial conc. of strong base

Answer 23

All bases, except for hydroxides of group 1 and 2, are weak - made up of molecules that react w/ water to release hydroxide ions General equation for their dissociation: B(aq) + H2O BH+(aq) + OH-(aq) - at equilibrium, most of the weak base molecules have not dissociated into ions - position of equilibrium lies to the left

Answer 24

- for weak acids and bases, equilibrium conc. of H3O+ ions or OH- ions are much lower than for strong acids and bases - these differences in conc. can be used to distinguish between solution of weak and strong acids and bases

Answer 25

Solutions that have equal concentrations - Weak and strong acids and bases of the same concentration - distinguished due to their different properties eg. pH, electrical conductivity, and in case of acids, by their reactions w/ active metals

Answer 26

Weak acids and bases have a lower conc. of mobile ions in solution- as they only partially ionise in solution - hence, are a poor conductor of electricity Strong acids and bases have a higher conc. of mobile ions in solution- completely ionise in solution - good conductors of electricity NB/ when comparing electrical conductivity of weak and strong acids and bases, solutions must be of equal conc.

Answer 27

Bases do not react with metals

Answer 28

Strong acids - weak conjugate bases - a stronger acid will ionise more - position of equilibrium lies to the right - conjugate base is reactively weak Weak acids- strong conjugate bases - conjugate base is relatively strong - equilibrium lies to the left

Answer 29

Refers to all types of acid precipitation | - can be classified as dry deposition eg. acidic gases and solid particles or wet deposition e.g. acid rain

Answer 30

Natural rainwater is acidic- pH of 5.6 - acidity is due to presence of carbon dioxide in the atmosphere - carbon dioxide reacts w/ water to form carbonic acid

Answer 31

- has pH of less than 5.0 - formed when acidic gases eg. sulphur dioxide and oxides of nitrogen dissolve in water in atmosphere to produce sulphuric acid and nitric acid

Answer 32

1. During lightning storms by reaction of nitrogen and oxygen (2 predominant atmospheric gases) 2. By reactions that take place in internal combustion engines - nitrogen reacts directly w/ oxygen at high temp. to produce nitrogen monoxide (a free radical- has an unpaired electron in valence shell of nitrogen atom) - takes place in both petrol and diesel engines; level of pollution is greater from diesel engines as operating temp. is higher - use of a catalytic converter in vehicle exhaust fumes reduces level of these emissions Nitrogen oxide undergoes further oxidation in atmosphere to produce nitrogen dioxide (also a free radical) - nitrogen dioxide reacts w/ water to form nitric and nitrous acid

Answer 33

- occurs naturally in the atmosphere as it's released during volcanic eruptions - also produced when coal and oil that contain sulphur are burned in power stations - sulphur is a contaminating presence in coal and fuel oil used in power stations - sulphur (present in coal or fuel oil) is oxidised during combustion process and forms sulphur dioxide

Answer 34

- sulphur dioxide can also undergo photochemical oxidation in the atmosphere - process takes place in water droplets where sulphur dioxide is dissolved, catalysed by particulates eg. soot and fine metallic particles - reaction is complex, and isn't a direct reaction w/ atmospheric oxygen - interactions w/ hydroxyl radicals, ozone or hydrogen peroxide are involved - sulphur dioxide and sulphur trioxide react w/ water in the atmosphere to form sulphurous and sulphuric acid

Answer 35

- acidic particles and gases fall to ground via dust and smoke in absence of precipitation - this deposition can be washed into streams, lakes or rivers, causing harm to biological systems

Answer 36

- can have serious consequences for living organisms eg. fish and trees - can enter aquatic ecosystems either directly eg. rain or indirectly as run-off - pH below 5.5, fish can't survive, and prevents fish eggs from hatching - aluminium ions leached from soil by acid rain, enter rivers and streams and have harmful effects on fish gills - fish exposed to aluminium ions secrete excess mucous around gills, preventing oxygen uptake, leading to death by asphyxiation - loss of some species can cause knock-on effect through food chain- adversely affecting other organisms - biodiversity within a lake or river can be reduced by acid deposition as they become dominated by acid-tolerant species

Answer 37

- determines which species of plants grown in a certain location - aluminium is present in soil at high pH values as insoluble aluminium hydroxide - when pH falls, aluminium ions are released into soil where it can damage roots of plants, preventing uptake of water - acid deposition also has potential to leech essential plant nutrients from soil

Answer 38

Statues and other architectural structures are often made from limestone or marble- both forms of calcium carbonate - calcium carbonate can react w/ sulphuric acid forming calcium sulphate, carbon dioxide and water - structures of iron, steel or aluminium can also be damaged by acid deposition - rate of rusting, being an electrolytic process, is increased by greater conc. of ions in acidic rainwater

Answer 39

- acid rainwater and moisture in air can adversely affect mucous membranes and lungs - causes irritation and possibly exacerbating symptoms for people w/ asthma and other respiratory conditions

Answer 40

A method of reducing amount of acid deposition | - involves removing sulphur oxides from exhaust gases once they have been formed by reacting w/ a base

Answer 41

A method of reducing amount of acid deposition | - involves removing sulphur before coal is combusted

Answer 42

A pre-combustion method by which sulphur is removed from refined petroleum products eg. gasoline, jet fuel, kerosene and diesel fuel before combustion - takes place at high temp. and pressures in presence of a catalyst - sulphur is removed from product in form of hydrogen sulphide

Answer 43

- a post-combustion method used in power stations - levels of sulphur dioxide emissions in flue gases can be reduced by passing them into a flue gas desulphurisation tower - in this tower, gases are passed through a sprayed aqueous suspension of calcium carbonate and calcium oxide - product is calcium sulphite, which is further oxidised to produce calcium sulphate

Answer 44

Soils and lakes whose pH has been significantly lowered by acid deposition can be treated w/ calcium hydroxide or limestone - neutralises acidity and raises pH

Answer 45

A reaction that involves both oxidation and reduction - The two processes always take place together - if one reactant is oxidised during a reaction, another must be reduced

Answer 46

- gain of oxygen - loss of hydrogen - loss of electrons - results in an increase in oxidation state

Answer 47

- loss of oxygen - gain of hydrogen - gain of electrons - results in a decrease in oxidation state

Answer 48

A species that oxidises other species - readily accept electrons - reduced in the course of the reaction NB/ an oxidising agent is reduced

Answer 49

A species that reduces other species - readily donate electrons - oxidised in the course of the reaction NB/ a reducing agent is oxidised

Answer 50

Oxidation states that are assigned to atoms in a compound give a measure of control that an atom has over electrons in the compound - concept of oxidation states assumes that atoms lose or gain electrons according to their electronegativity values, regardless of whether they actually form ions or not - if an atom loses control over electrons- oxidised - if an atom gains control over electrons- reduced Written with a sign (+/-) and a numerical value + = atom has lost electron control - = atom has gained electron control Numerical value= takes into account no. of electrons that atom has lost or gained control over

Answer 51

A number which, together with its sign, indicates the gain or loss of electron control of an atom during a reaction - oxidation NUMBER is a numerical part of that value - it is used as a Roman numeral in the chemical formula of a compound

Answer 52

1. Free elements (O2, Cl2, N2) have oxidation state = 0 2. Sum of oxidation states of all atoms in a compound = net charge on compound 3. Alkali metals (Li, Na, K, Rb and Cs) in compounds = +1 4. Fluorine in compounds is always -1 5. Alkaline earth metals (Be, Mg, Ca, Sr, Ba and Ra) and Zn = +2 6. Hydrogen in compounds = +1, except in certain metal hydrides = -1 7. Oxygen in compounds = -2, except in peroxides = -1 8. Halogens in compounds = -1 9. Charge on a metal ion = same as its oxidation state 10. Sum of oxidation states in a polyatomic ion must add up to charge on ion

Answer 53

Some atoms can show variable oxidation states | - includes transition elements and non-metal elements

Answer 54

Occurs when same species is oxidised and reduced simultaneously during a reaction to form 2 different products - eg. catalytic decomposition of hydrogen peroxide

Answer 55

the transfer of an electron pair, with the subsequent formation of a coordinate bond

Answer 56

acids and bases are defined in terms of the transfer of protons (H+ ions)

Answer 57

According to the Lewis theory, an acid is an electron pair acceptor and a base is an electron pair donor

Answer 58

an electron pair acceptor | - electrophiles

Answer 59

an electron pair donor | - nucleophiles

Answer 60

Complex ions are formed when a ligand uses a lone pair of electrons to form a coordinate covalent bond w/ a central metal ion - in this complex ion, the ligands act as Lewis bases, and the central metal ion acts as a Lewis acid

Answer 61

a compound formed by the reaction of 2 similar monomers

Chapter 8/ 18 Flashcards

Acids and bases (85 cards)