Acids & Bases, Electrochemical Cells, Transition Metals, Aqueous ions Flashcards

Question

What does the Standard Electrode potential value of a half cell tell you about its redox ability?

Answer 1

- The more positive the value of the standard electrode potential, the greater the tendency for reduction, they are strong oxidising agents -The more negative the value of the standard electrode potential, the greater the ability of the elements to be oxidised, they are strong reducing agents e.g.

Answer 2

- changes in temperature, pressure or concentration will effectively change the position of the redox equilibrium and thus the electrode potential of the half-cell - If the position of equilibrium is shifted in favour of the **forwards reaction** (the reduction),the electrode potential becomes **more positive** - if instead the position of equilibrium is shifted in favour of the **backwards reaction** (the oxidation), the electrode potential becomes **more negative** - therefore the cell that is most likely to be oxidised is the one with the most negative standard electrode potential.

Answer 3

Double vertical solid line - Salt Bridge Vertical Solid Line - phase boundary, e.g between an aqueous solution and a solid - Species with eg HIGHEST oxidation state is written **closest** to the salt bridge - The half cell with the more *negative* potential goes to the **left** - platinum electrode is used when no solid electrodes are in the half cell

Answer 4

- electrons flow from the more negative electrode to the more positive electrode - causing an EMF EMF = E⦵ (reduced) – E⦵ (oxidised) or EMF = E⦵ (right electrode) – E⦵ (left electrode)

Answer 5

- The electrons flow from the more reactive element (most negative electrode potential) to the less reactive element (metal with the most positive electrode potential)

Answer 6

- A positive overall EMF indicates that a reaction is feasible - however this prediction is only correct under standard conditions - to determine whether a reaction is likely to occur reaction conditions must also be considered - i.e a reaction may be feasible in terms of EMF but have a very high activation energy.

Answer 7

ADVANTAGES Cheaper Easy to use and has a wide range of Applications Portable and easy to replace DISADVANTAGES once the reactants have been used up, the battery must be disposed of toxic chemicals can leach from landfill sites into water sources the casing of the battery can be corroded by the electrolyte, causing leakages Non-sustainable - the materials to make batteries are finite

Answer 8

ADVANTAGES - have a longer life-span than non-rechargeable batteries - Can be recharged multiple times - more energy efficient as chanting takes less energy than making new batteries DISADVANTAGES Cost more than non-rechargeable batteries Need to be regularly recharged Not all appliances are suitable to be used with rechargeable batteries

Answer 9

ADVANTAGES only reaction product is water all bond energy is converted in to electrical energy (more efficient than conventional engines) no pollutants can produce enough electricity to run vehicles which are much lighter and smaller than conventional engines and batteries DISADVANTAGES hard to store Hydrogen gas (needs to be under high pressure) highly **flammable/explosive** hydrogen is obtained via electrolysis (needs fossil fuels) hydrogen is also obtained directly from fossil fuels low energy density (for the same volume of other fuels hydrogen produced less)

Answer 10

- Rechargeable Batteries

Answer 11

- when the battery is being used it operates like your standard non-rechargeable battery where a reactive electrode releases electrons which reduce ions at another electrode - when being recharged, the reverse reactions occur and electrons flow in the opposite direction from the electricity supply to the e.g. lithium ions.

Answer 12

- a fuel cell produces electricity by using a fuel on the positive electrode and an oxidant on the negative electrode. They react in the presence of an electrolyte - as long as there is a continuous supply of fuel, the cells can operate continuously - most common in automotive industry e.g Hydrogen-Oxygen fuel cell pic 1. Hydrogen enters at the negative electrode and releases electrons (oxidised by hydroxide ions to water) 2. The electrons flow through the external circuit (electrons flow to positive electrode) 3. The electrons are accepted and released hydroxide ions (electrons are accepted by the oxygen entering at the positive electrode) 4. The hydroxide ions travel to the negative electrode (hydroxide ions travel through the semi permeable membrane to negative electrode) 5. cycle repeats

Answer 13

- an ionic compound that is melted or dissolved in water

Answer 14

- acid-base indicators act as **weak acids** where the unionised acid and its conjugate base have **different colours** - the end point of a titration is the point at which an indicator changes colour - though due to indicators working of small ranges of pH, it may not be **exactly** at the equivalence point.

Answer 15

The colour change occurs at the **equivalent point** - the colour change **must** occur at the **equivalence point** The indicator has a **narrow pH range** - the indicator chosen needs to cover a narrow pH range The indicator shows a sudden distinct colour change - only a few drops needed for a distinct colour change at neutralisation point

Answer 16

Acid: STRONG Base: STRONG pH range at equivalence point - 3-11 suitable indicators - ANY Acid: WEAK Base: STRONG pH range at equivalence point - 7-11 suitable indicators - phenol red(6-8), thymol blue(9-10), phenolphthalein (8-10) Acid:STRONG Base:WEAK pH range at equivalence point - 3-7 suitable indicators - methyl orange (3-4), methyl red (4-6) Acid:WEAK Base:WEAK - no clear equivalence point - no suitable indicator

Answer 17

- oxidation state: maximum no. of electrons that can be lost without energy needed to remove electrons> energy recovered in bonding - due to the large no. of valence electrons of d-block elements it would require a lot of energy to remove them all - thus they can only give up some of their d-electrons (after removing their 4s ones)

Answer 18

- A Complex Ion is a metal cation surrounded by ligands dative-covalently bonded to it

Answer 19

- A Ligand is a species which can use its lone pair of electrons to form a dative covalent bond with a transition metal

Answer 20

- they must have high charge density, and thus be able to attract electrons from ligands - they must have empty orbitals of low energy, so that they can accept the lone pair of electrons from the ligands

Answer 21

- The number of lone pairs of electrons which a cation can accept is known as the coordination number of the metal cation

Answer 22

Monodentate - Can form only **ONE** dative covalent bond **per** ligand e.g H2O, Cl- Bidentate - Can form only **TWO** dative covalent bonds **per** ligand e.g 1,2-diaminoethane, ethandionate Multidentate - Can form **multiple** dative covalent bonds **per** ligand e.g EDTA^4-, Haem

Answer 23

- Square planar complexes show cis-trans isomerism only - ligands can either be adjacent or opposite to one another if there are two different ligands attached Octahedral - Octhaedral complexes also show cis-trans isomerism but also Optical Isomerism octahedral complexes show cis-trans isomerism when: - they contain for ligands (or two bidentate ligands) of one type and two ligands of another type octahedral complexes show optical isomerism when: - there are three bidentate ligands - two bidentate ligands and two monodentate ligands - one hexadentate ligands

Answer 24

- 6-coordinate complexes are all octahedral - most complexed involving multidentate ligands are octahedral - 4-coordinate complexes are generally tetrahedral, and are formed with **larger ligands** such as **Cl-** - Larger Ligands cannot fit around the transition metal so easily so form smaller complexes - some 4-coordinate complexes in the case of Pt and Ni form **square planar** structures - 2-coordinate complexes are generally linear (and typically form with Ag^+ ions)

Answer 25

- Larger ligands cannot fit around the transition metal so easily and hence form smaller complexes - this will typically be tetrahedral, linear or square planar (if Pt or Ni)

Answer 26

- Transition metal ions are coloured because d-electrons can absorb light and get excited into higher energy d-orbitals - the resultant light is thus missing certain frequencies and is hence coloured - the d-orbitals must be **partially filled**. If the d-orbitals are empty then there are no electrons which can be excited and if it is full then there are no empty orbitals which electrons can be excited to (making them colourless).

Answer 27

- The ligand - The coordination number - the oxidation state of the metal - the identity of the metal*

Answer 28

1. Substitution by similar size ligands -> no change in coordination number 2. Substitution by larger/smaller ligands -> may cause change in coordination number e.g H2O (octahedral) vs Cl- (tetrahedral) 3. Substitution by bidentate/multidentate ligands - multidentate ligands will almost always replace monodenate ligands at a metal centre - CHELATE EFFECT - because same number of co-ordinate bonds broken and made therefore ΔH is negligible - Large increase in entropy (greater no. of atoms as products)

Answer 29

- There are more species in the products than the reactants when multidentate ligands substitute monodentate ligands - The **entropy** of the system thus **increases**, and multidentate complexes are therefore more stable then complexes involving misidentified ligands

Answer 30

- The pH - **oxidation** is favoured by **alkaline** conditions and **reduction** is favoured by **acidic** conditions - The choice of Ligand

Answer 31

- Ligand exchange is when one ligand in a complex is replaced by another - Ligand exchange forms a new complex that is more stable than the original one - The ligands in the original complex can be partially or entirely substituted by others

Answer 32

- all 5 of the d-orbitals due to being incomplete can exist at a different energy levels - hence why electrons can be excited and excited between them - if the gaps between them correspond to visible light, they will absorb that wavelength of light, which is the colour we see of the complex

Answer 33

- Haem consists of a Fe2+ ion and a tetradentate ligand - the complex is found with a protein - globin (which forms a 5th coordinate bond) - and oxygen (6th coordinate bond) - it is responsible for carrying oxygen in the blood throughout the human body - Carbon monoxide is a similar size and shape to oxygen AND forms a much **stronger** bond with iron - thus it **displaces** oxygen from the complex - this reduces the bloods ability to carry oxygen around the body - making it poisonous

Answer 34

- form complex ions - form coloured ions - have variable oxidation states - have catalytic activity/act as catalysts

Answer 35

- A simple Colorimeter can be used to determine the concentration of coloured ions - because complex ions form coloured ions due to the absorption of light waves causing electron excitation - the greater the absorption of light of a substance containing complex ions, the greater the concentration of those ions

Answer 36

- In the same ‘Phase’ as reactants e.g 2I- + S2O82- —> I2 + 2SO42- S2O82- + 2Fe2+ —> 2SO42- + 2Fe3+ 2Fe3+ + 2I- —> I2 + 2Fe2+ both negatively charged so require a lot of energy to overcome that electrostatic repulsion by adding an Fe2+ catalyst this provides an alternative energy pathway for the reaction to occur

Answer 37

- reactants diffuse onto surface of catalyst - reactants are ‘absorbed’ onto catalyst - reaction starts and intermediate gets formed - reaction completes and product gets formed

Answer 38

- d-subshell splits into 2 when ligands bond with the central metal ion - due to the lone pairs on the ligands repulsing some of the electrons in the orbitals more than others

Answer 39

- the central metal ion and its oxidation state - the type of ligand - the coordination number

Answer 40

- some frequencies of visible light are absorbed by transition metal complexes - dependent on delta E - any frequencies not absorbed are reflected - the combination of these reflected/transmitted frequencies create a **complimentary colour** that we observe

Answer 41

- The complex may have a full or empty 3d sub-shell - no electrons can migrate to the higher energy level - thus no electrons excited by absorbing EM waves - so all wavelengths reflected so complexes are seen as white or colourless

Answer 42

- Transition metal complexes are analysed using colorimetry - compliments of the colours absorbed by the solution - measures concentration of transition metal ions in solution

Answer 43

1. colorimeter must be set to zero - this is done by measuring the absorbance of a blank sample (i.e the solvent used to dissolve sample) 2. white light is filtered into a narrow range of frequencies. Monochromatic light is produced - the colour form the filter must be absorbed by the metal ion 3. monochromatic light passes through the sample and **some** light is absorbed, the same is held in a vessel - a **cuvette** - the cuvette must be frosted on tel sides and colourless on the other 4. light not absorbed travels to the detector, the detector measures the absorbance (via comparing it to the blank sample)

Answer 44

- by taking a range of known different concentrations of the transition metal solution - the absorption is measured for each one and the results are plotted - samples are made by diluting different concentrations of the metal ion - you must use the same metal ion as the one to be tested (a pipette is used to insure accurate volumes)

Answer 45

- A colour change occurs when ligands are substituted/exchanged in a complex -

Answer 46

- Different Ligands can form different **strength** bonds to the metal ion - If a substituted Ligand forms a stronger bond with the complex ions the reaction is not easily reversed because the complex formed is more stable - multidentate ligands form complexes that are more stable than monodentate ligands

Answer 47

- an increase in entropy during a substitution forms a more stable complex - this increase in stability is the chelate effect

Answer 48

- it occurs because when a monodentate is substituted by a bi/multidentate a solution with more particles is formed, causing an increase in entropy

Answer 49

- you must recall all of them !!

Answer 50

- Vanadium ions can be reduced using zinc in acidic solution

Answer 51

- Yellow to Blue

Answer 52

- blue to green

Answer 53

- green to yellow

Answer 54

- redox potential shows how easily an ion is reduced - The **least** stable ions have the **largest** redox potential and are more likely to be reduced - The **most** stable ions have the **smallest** redox potential and are least likely to be reduced

Answer 55

- Standard electrode potentials are always measured in **aqueous** solutions. - The metal ion is surrounded by water molecules

Answer 56

Ligands - non-water ligands can alter the redox potential depending on whether they form a stronger bond with the metal ion pH - the pH of the solution effects the size of redox potentials with some reactions - the more acidic the solution the **larger** the electrode potentials. - this means the ion is more **easily reduced**

Answer 57

- Ketones are fully oxidised, aldehydes are not - Tollen’s is a good oxidising agent so it can oxidise the Aldehyde further - it’s half equation has a large potential value which means the Ag+ ion is easily reduced to silver metal ( Ag+(aq) + e- —> Ag(s) = +0.8V ) - Tollen’s is made by reacting aqueous ammonia with aqueous silver nitrate

Answer 58

- The contact process uses vanadium(V) as a catalyst in the formation of sulfur trioxide to later form sulfuric acid - Vanadium acts as a heterogenous catalyst - roast sulfur in air S (s) + O2 (g) → SO2 (g) SO2 (g) + V2O5 (s) → V2O4 + SO3 (g) O2 (g) + 2V2O4 (s) → 2V2O5 (s) 2SO2 (g) + O2 (g) ⇌ 2SO3(g) - The SO3 is then bubbled through water to form H2SO4

Answer 59

N2 (g) + 3H2 (g) ⇌ 2NH3 (g) (Iron pellets are used as the catalyst to provide a large surface area) - the surface of the iron attracts electrons in the hydrogen and nitrogen - The reactants bind to the active sites of the catalyst, adsorption (temporary bond with one reactant on surface) -This leads to an increase in concentration of reactant particles at the catalyst surface, increasing the frequency of collisions - Adsorption causes bonds within the reactant molecules to weaken and break. - New bonds form between the reactants on catalyst surface. - The product leaves the active site, and frees it up for new reactants molecules to adsorb. (desorption)

Answer 60

- Heterogenous catalysts can be poisoned by impurities - Impurities can bind to the surface of a catalyst and block the active sites for the reactants to adsorb - catalytic poisoning reduces the surface area of the catalyst for the reactant to add to, this slows the reaction

Answer 61

- capability of all solid substances to attract to their surfaces molecules of gases or solutions with which they are in contact.

Answer 62

- Less product is made - The Catalyst needs to be replaced often - increased cost of the chemical process

Answer 63

If the the adsorption is too strong, the products will not be released from the catalyst surface. This can happen with metals like tungsten. If the adsorption is too weak the reactants do not adsorb in a high enough concentration to react. Ni and Pt have the right strength for adsorption, and are most useful as heterogeneous catalysts.

Answer 64

- Catalysts can be poisoned - thin layers of Heterogenous Catalysts so wears away easily - Catalysts do not work at low temperature

Answer 65

- Increase Surface Area - Use powder or Pellets - Coat the surface of a hollow matrix

Answer 66

- Transition Metals are good catalysts because they have variable oxidation states - e.g can work as both a reducing agent and oxidising agent in the same reaction aka REDOX like Fe ions

Answer 67

- Autocatalysts are catalysts produced from a reaction that increase the rate of the reaction after their production.

Answer 68

- The reaction between KMnO4 and ethanedioate - the Mn2+ produced behaves as a catalyst - thus the reaction is **slow** at first but is **much faster** after a **little** of the products are formed.

Answer 69

- They have **empty d-orbitals** of low energy which can accept **electron pairs**

Answer 70

- The presence of **Ligands** causes the **d-orbitals to split.** - In the presence of visible light, electrons are excited from **low energy d-orbitals** to **high energy d-orbitals**, absorbing the light in the process. - resulting in coloured light

Answer 71

- They do **not** form any **stable ions** with **partially filled** d-orbitals

Answer 72

- Due to the low effective nuclear charge on scandium enables all three valence electrons to be removed easily

Answer 73

- Due to the high effective nuclear charge on zinc prevents any 3d electrons from being removed

Answer 74

- It has four different ligands (or two bidentate Ligands ) of one type, and two ligands of another type

Answer 75

- In this reaction water acts as a weak base, a lone pair donor - The (hexa) aqua ions donate a proton from one of the water ligands to the water - this deprotonates the aqua ion, changing its overall charge

Answer 76

- Three Bidentate ligands - Two Bidentate Ligands and two monodentate ligands ( **cis** isomer only) - One hexadentate ligand

Answer 77

- Hydroxide ions are a strong base - it pulls a proton away from the water ligands - it removes more than one due to its base strength - in all cases a hydrated hydroxide will form - the hydroxide are all insoluble - so a precipitate forms when another hydroxide (i.e NaOH/KOH) is added

Answer 78

- transition metal hydroxides convert back to their hexaaqua complex by the addition of acids - Metal hydroxides that dissolve in acid but not excess alkali are **basic** (e.g [Fe(OH)2(H2O)4] ) - Meral Hydroxides which dissolve in acid and in excess alkali are **amphoteric**

Answer 79

- Ammonia is a stronger base than water so can also cause deprotonation of hexaaqua complex’s to form hydroxide precipitates - Though ammonia is not sufficiently strong enough to cause further deprotonation

Answer 80

- Carbonate ions are bases and can deprotonate the +3 transiton metal aqua ions to form a hydroxide precipitate - The carbonate ions are converted into carbon dioxide gas - for +2 ions they do not deprotonate readily so do not behave as acids in the presence of carbonate ions - instead they form carbonate precipitates

Answer 81

MnO4- (+4) -> Purple Mn2+ (+2) -> **Pale** Pink MnO4- + 8H^+ + 5e -> Mn2+ + 4H2O

Answer 82

- The end point is detected by the failure of the purple colour to disappear, leaving a pink colour, showing there are no longer MnO4- ions being reduced - The gradual disappearance of the pink colour is much harder to detect than the sudden appearance of the pink colour due to KMnO4 being in the burette rather than a conical flask

Answer 83

- Diammine silver [Ag(NH3)2]+ is the active ion in **tollen’s reagent** - It is reduced to silver by reducing sugars and aldehydes and produces a silver mirror

Answer 84

- Oxidising agents in aqueous solution can be determined by titrating against standard solutions of reducing agents - Reducing agents in aqueous solution can be determined by titrating against standard solutions of oxidising agents

Answer 85

- It is only an effective oxidising agent in acidic medium

Answer 86

- HCl : Cl- is a reducing agent and will react with the MnO4- before it can react with the reducing agent being investigated - HNO3 : NO3- is an oxidising agent and will react with the reducing agent before the MnO4- can - CH3COOH : weak acid so will not release enough H+ ions this Sulfuric Acid is typically used

Answer 87

- The ability of transition metals to form more than one stable oxidation state means they can accept and lose electrons easily - this enables them to catalyse certain redox reactions - because they can be easily oxidised or reduced due to their no. of different oxidation states of similar stability

Answer 88

normal/base colour: **Pale** Green OH- little: **Dark** Green precipitate OH- excess: **Dark** Green precipitate NH₃ little: **Dark** Green precipitate NH₃ excess: **Dark** Green Gelatinous precipitate CO₃²⁻/base : **Dark** Green precipitate + effervescence

Answer 89

normal/base colour: Orange OH- little: Red Brown Gelatinous OH- excess: Red Brown precipitate NH₃ little: Red Brown precipitate NH₃ excess: Red Brown precipitate CO₃²⁻/base : Red Brown precipitate + effervescence

Answer 90

normal/base colour: Blue OH- little: **Light** Blue precipitate OH- excess: **Light** Blue precipitate NH₃ little: **Dark** Blue precipitate NH₃ excess: **Dark** Blue solution CO₃²⁻ /base : **Light** Blue precipitate (no effervescence)

Answer 91

normal/base colour: **Colourless** OH- little: White precipitate OH- excess: Colourless solution NH₃ little: White precipitate NH₃ excess: White precipitate CO₃²⁻ /base : White precipitate + effervescence

Answer 92

- The end point is simply when a colour change occurs as the solution in a titration gets to a particular pH. whereas - The equivalence point refers to the point at which chemically equivalent amounts of acid and base have been mixed in the solution, not the pH of the solution.

Answer 93

The equivalence point of a titration is the point at which 'chemically equivalent' amounts of acid and base have been mixed.

Answer 94

- the end point of a titration is when enough ‘titrant’ has been added to make the indicator change colour (due to getting to a particular pH) - Different indicators can change colour at different pH values, this is why the same indicators aren’t always used for different titrations.

Answer 95

At the equivalence point, the solution should only contain a salt and water.

Answer 96

- To get the end point as close to the equivalence point as possible - This can be done by using Indicators which change colour within the pH range for which equivalence occurs

Answer 97

- In a titration, we want the end point to be as close to the equivalence point as possible. - If a strong acid is titrated with a strong base, the resulting solution has a pH of 7. - If the indicator changes colour at pH 7, the end point = the equivalence point of the solution.

Answer 98

The neutralisation point of a titration is the point at which just the right amount of titre has been added to make the pH of the solution 7 (neutral).

Answer 99

if a Strong Acid is titrated with a Weak Base, at the equivalence point, the solution produced doesn’t have a pH of 7. (solution can still be slightly acidic or alkaline depending on further reactions of ions) - The solution is not neutral, even though the moles of acid and base have been perfectly mixed. - ∴ If an indicator that changes colour at pH 7 was used, the end point of the titration would not be the same as the equivalence point.

Answer 100

- Strong Acid, Strong Alkali

Answer 101

- Strong Acid, Weak Base

Answer 102

- Weak Acid, Strong Base - Buffer region is as a result of the temporary formation of a buffer during the titration - Buffers resist changes in pH thus the change in pH is slow

Answer 103

- Weak Acid, Weak Base - no clear end point

Answer 104

A solution which is able to resist changes in pH when small volumes of acid or base are added.

Acids & Bases, Electrochemical Cells, Transition Metals, Aqueous ions Flashcards

(130 cards)