Chemistry A Level OCR A; Transition elements

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Electron configurations of elements in the first row of the d-block

Why is chromium and copper not follow the expected electron configuration of electrons in their orbitals?

Increased electron stability where,

- Half filled d5 sub shell give greater stability than 4s2

- Full filled d10 sub shell give greater stability than 4s2

Which subshell will lose their electrons first to form d-block ions?

d-block elements will lose electrons from their 4s subshell first, therefore;

- When forming an atom from an ion, 4s subshell gets filled first

- When forming an ions from an atom, 4s subshell loses electrons first

What is the exact definition of a transition element?

d-block elements that for at least one ion with a partially filled d-orbital

Which d-orbtial elements are not classified as a transition element?

- Scandium

- Copper

What are the properties of the transition metals and their compounds?

- Transition elements form compounds where the transition elements have a different oxidation state

- Transition compounds form coloured compounds based on their oxidation state

- The transition elements and the compounds can act as catalysts

Can transition elements form compounds with more than one oxidation state?

Yes, i.e. Iron (II) and Iron (III)

What species is often a strong oxidising agent relative to one of its elements being a transition element?

A species with a transition element in it's highest oxidation state

When transition metals are dissolved in water, what visible change occurs?

The solutions colour forms based on the transition element and the oxidation state

Why does a transition element dissolved in water form a colour?

Partially filled d-orbitals of the transition metal ion.

What is used as a catalyst for the haber process?

Iron catalyst

What is used as a catalyst in the Contact process?

Vandium oxide

What is used as a catalyst in the manufacture of margarine?

Nickel

What is the catalyst for the decomposition of hydrogen peroxide?

Manganese (IV) oxide

What can determine the visible change that a catalyst speeds up a reaction?

An indicator

What is one of the most important property of the d-block elements?

The ability to form complex ions

Are complex ions restricted to d-block elements?

No, other elements can form complex ions

How is a complex ion formed?

When one or more molecules or negatively charged ions bond to a central metal ion

What are one (or more) molecules or negatively charged ions forming a coordinate (dative) bond known as?

A ligand

What is a coordinate covalent bond?

A covalent bond in which one atom contributes both of the electrons to form a covalent bond

What is a coordination number?

The number of coordinate bonds attached to the central metal ion

What is the coordiantion number of [Cr(H20)6]3+?

6, as there are 6 molecules of water that donate a pair of electrons forming a coordinate (dative) bond

What is the exact definition of a ligand?

- Any molecule or ion that can donate a pair of electrons to a central metal ion, forming a coordinate (dative) bond

- They can be neutrally charged or negatively charged

What is a monodentate ligand?

This term is applied to a ligand if and only if the ligand is able to donate one and only one pair of electrons to the central metal ion

What are five monodentate ligands?

- Water

- Ammonia

- Chloride

- Cyanide

- Hydroxide

What is a bidentate ligand?

A ligand that can donate two pairs of electrons to the central metal ion through the formation of two coordinate bonds

What are two most common examples of bidentate ligands (Hint; one has a neutral charge one doesn't)

- 1-2-diaminoethane (neutral charge)

- ethandioate (2- charge)

Draw the structure of 1,2-diaminoethane

Draw the structure of ethandioate

Draw the complex ion of nickel transition element with 1,2-diaminoethane as a bidentate ligand. The nickel has an oxidation number of 2+

You must give;

- The overall oxidation number

- The coordinate number

- 1,2-diaminoethane is neutral therefore the overall charge stays as 2+

- Each ligand forms two coordinations bonds therefore the coordiantion number is 6

What does the shape of a complex ion depend on?

The coordination number

What are the most common coordination numbers?

- Four

- Six

What would a coordination number of six give a shape of?

An octahedral shape

What would a coordination number of four give a shape of?

- Tetrahedral

- Square planar

What are the bond angles of an octahedral shape?

90˚

What are the bond angles in a tetrahedral shape?

109.5˚

When would a complex ions form a square planar shape?

With transition metals with eight d-electrons in the highest energy level d-sub-shell

Which three transition elements will form a square planar shape?

- Platinum (II)

- Palladium (II)

- Gold (III)

What is stereoisomerism?

Stereoisomers with the same structural formulae but a different arrangement of atoms in space

Why two types of stereoisomerism can complex ion display?

- E/Z isomerism

- Optical isomerism

What does stereoisomerism depend on in a complex ion?

Number and type of ligands that are attached to the central metal ion and shape of the complex

Which complex ions can show cis-trans stereoisomerism?

- Four-coordinate and six-coordinate complex ions with two different monodentate ligands

- Some six-coordinate complex ions with monodentate and bidentate ligands

What complex ions can show optical stereoisomerism?

Some six-coordinate and four-coordinate complex ions with mondentate and/or bidentate ligands

Draw the cis and trans isomers of [Pd(NH₃)₂Cl₂], include;

- All angles, if any

- Arrangement in space, if any

- Charges, if any

Draw the cis trans structures of [Co(NH₃)₄Cl₂]⁺ include;

- All angles, if any

- Arrangement in space, if any

- Charges, if any. Cobalt is 3+ here

Draw the cis trans structures of [Co(NH₂CH₂CH₂NH₂)₂Cl₂]⁺ , include;

- Charges

- Arrangment in space

- Bond angles are not necessary

- Remember, the positioning of the chloride ligands determine the arrangement of space of the atoms and therefore the name

Draw the optical isomers of [Co(NH₂CH₂CH₂NH₂)₂Cl₂]⁺

Remember to think optical isomers as your hands, they are mirror structures

What is the definition of an optical isomer?

The optical isomers (enantiomers) are two non-superimposable mirror images of each other

Show the optical stereoisomerism of [Ru(NH₂CH₂CH₂NH₂)₃]²⁺, include

- The charges

- The arrangement of ligands in space

Give the definition of a ligand (repeated question)

A molecule or ion that donates a pair of electrons to form a dative (coordinate) bond to a central metal ion

What occurs in a ligand substitution reaction? (general definition)

One ligand is replaced by another ligand in a complex ion

Make sure to do Lots and Lots of paper questions on complex ion naming.

Nearly there, keep pushing

What occurs when copper(II) sulphate dissolves in water?

A pale blue complex ion if formed in aqueous solution

What colour change occurs when aqueous [Cu(H2O)6]2+ is added with an excess of aqueous ammonia?

Pale blue complex forms a dark blue solution

Draw the equation that occurs when aqueous [Cu(H2O)6]2+ is added with an excess of aqueous ammonia

[Cu(H₂O)₆]²⁺ (aq) + 4NH₃ (aq) --> [Cu(NH₃)₄(H₂O)₂]²⁺ (aq) + 4H₂O (l)

- Remember that [Cu(H₂O)₆]²⁺ is a pale blue complex of solution and is an octahedral complex ion

- [Cu(NH₃)₄(H₂O)₂]²⁺ is a dark blue complex solution and is an octahedral complex ion

How should you add excess aqueous ammonia to your aqueous complex copper ion? Why?

Dropwise, to record any observations present

Draw the structures of both [Cu(H₂O)₆]²⁺ and [Cu(NH₃)₄(H₂O)₂]²⁺, include;

- Arrangement in space, if any

- Charges present, if any

- Bond angles are not needed

What are the two observations that occur during the ligand substitution of copper (II) sulphate to [Cu(H₂O)₆]²⁺ and [Cu(NH₃)₄(H₂O)₂]²⁺?

- Firstly, a precipitate of Cu(OH)₂ will form first

- The precipitate will then dissolve in the excess of ammonia to form the dark blue solution

What colour change occurs when an excess of hydrochloric acid is added to a solution containing [Cu(H₂O)₆]²⁺?

The pale blue complex ion solution turns to a green solution (no other product has formed) then a yellow solution

What occurs when an excess of hydrochloric acid is added to a solution containing [Cu(H₂O)₆]²⁺? (substitution), Also draw the structure of the product giving the arrangement of chloride ions, if any and charges, if any

- Six of the water ligands have been replaced by chloride ligands

- The change has changed as each chloride ligand provides -1 to the 2+ giving an overall change of 4- as [Cu(Cl)₄]² ⁻

Why is there a coordination number change from six water ligands to four chloride ligands?

- Chloride ligands are much large in size than water ligands, fewer chloride ligands can fit around the central metal ion

Draw the equation of the reaction of [Cu(H₂O)₆]²⁺ with excess hydrochloric acid to form [Cu(Cl)₄]² ⁻

[Cu(H₂O)₆]²⁺ (aq) + 4Cl⁻ (aq) <--> [Cu(Cl)₄]² ⁻ (aq) + 6H₂O (l)

Why has the charge number in [Cu(Cl)₄]² ⁻ changed from 2+?

As each chloride ion represents a ⁻ charge

What products forms when chromium (III) Potassium Sulphate, KCr(SO₄)₂.12H₂O is dissolved in water?

- The complex [Cr(H₂O)₆]³⁺ is formed

- The complex [Cr(H₂O)₅SO₄]⁺ is formed

What colour is the [Cr(H₂O)₆]³⁺ complex?

A pale purple solution

What colour is the [Cr(H₂O)₅SO₄]⁺ complex?

A green solution

What if formed when [Cr(H₂O)₆]³⁺ reacts with excess aqueous ammonia?

[Cr(NH₃)₆]³⁺ complex ion is formed

Show the equation for the ligand substitution equation of [Cr(H₂O)₆]³⁺ with excess aqueous NH₃

[Cr(H₂O)₆]³⁺ (aq) + 6NH₃ (aq) --> [Cr(NH₃)₆]³⁺ (aq) + 6H₂O (l)

What toxic molecule can bind to haemoglobin to the haem group?

Carbon monoxide can bind to the Fe²⁺ to form carboxyhaemoglobin

What type of reaction is occurring when carbon monoxide binds to the Fe²⁺ haem group?

A ligand substitution reaction

Is the process of carbon monoxide binding with haemoglobin reversible? Why or Why not?

No, as the ligand bonding from carbon monoxide to haemoglobin is very strong

What can increased carbon monoxide concentrations in the blood lead to in a human?

Death

What is a precipitation reaction?

When two aqueous solutions react together containing ions to form a insoluble ionic solid known as a precipitate

What two common solutions will transition metals react with to form precipitates?

- Aqueous sodium hydroxide

- Aqueous ammonia

Which four ions can react with aqueous sodium hydroxide to form an insoluble precipitate?

- Cu²⁺ (aq)

- Fe²⁺ (aq)

- Fe³⁺ (aq)

- Mn²⁺ (aq)

What are the reaction observations of OH⁻ (aq) with Cu²⁺ (aq)?

Draw the equation

- Blue solution reacts to form a blue precipitate of copper (II) hydroxide

- Precipitate is insoluble in excess sodium hydroxide

What are the reaction observations of OH⁻ (aq) with Fe²⁺ (aq)?

Draw the equation

- Pale green solution reacts to form a green precipitate of iron (II) hydroxide, insoluble in excess sodium hydroxide

- Surface of the solution turns brown as Fe (II) is oxidised to Fe (III)

What are the reaction observations of OH⁻ (aq) with Fe³⁺ (aq)?

Draw the equation

- A pale solution reacts to form an orange brown precipitate of Iron (III) hydroxide

- Precipitate is insoluble in excess sodium hydroxide

What are the reaction observations of OH⁻ (aq) with Mn²⁺ (aq)?

Draw the equation

- Pale pink solution reacts to from a light brown precipitate of Manganese (II) hydroxide, darkens on standing in air

- Precipitate is insoluble in excess sodium hydroxide

What are the reaction observations of OH⁻ (aq) with Cr³⁺ (aq)?

Draw the equations

- Violet solution reacts to form a grey-green precipitate of chromium (III) hydroxide

- Precipitate IS soluble in excess sodium hydroxide

In excess ammonia, can precipitate Cu(OH)₂ dissolve? (repeated question)?

Yes

What colour does the Cu(OH)₂ precipitate dissolved in excess ammonia form?

Deep dark blue with the formula [Cu(NH₃)₄(H₂O)₂]²⁺

Show the equation of chromium with hydroxide to form a precipitate

Cr³⁺(aq) + 3OH⁻ (aq) --> Cr(OH)₃ (s)

What colour is the Cr(OH)₃ precipitate?

Green precipitate

What does Cr(OH)₃ precipitate dissolving in excess ammonia form?

[Cr(NH₃)₆]³⁺

What colour is [Cr(NH₃)₆]³⁺ in solution?

Purple

Can Fe²⁺ (aq), Fe³⁺ (aq), Mn²⁺ (aq) also react with aqueous ammonia?

Yes

Are the precipitates of Fe²⁺ (aq), Fe³⁺ (aq), Mn²⁺ (aq) and ammonia able to dissolve in excess ammonia ?

No

What are the two ions used in a redox titration?

- Fe²⁺ (aq)

- MnO₄⁻

What occurs to Fe²⁺ (aq) in the redox titration?

Fe²⁺ (aq) is oxidised to Fe³⁺ (aq)

MnO₄⁻ (aq) is reduced to Mn²⁺ (aq)

Show the full equation in the redox titration

Wha colour change occurs of the solution of MnO₄⁻ (aq) ions?

Purple colour to colourless

Why is Fe²⁺ (aq) oxidised and MnO₄⁻ reduced?

As E⦵ is more positive for for MnO₄⁻ (aq) than for Fe²⁺ (aq)

What occurs when Fe³⁺ (aq) ions reacts with I⁻ (aq)? Show the full equation and the colour changes

Why is Fe³⁺ (aq) or Fe²⁺ (aq) reduced in the reaction with I⁻ (aq)?

- As both Fe³⁺ (aq) and Fe²⁺ (aq) has less negative E⦵ value than I (aq)

- Both Fe³⁺ (aq) and Fe²⁺ (aq) therefore have a less reactivity to undergo oxidation and lose electrons

As the E⦵ value becomes more positive, what occurs with the probability of oxidation

As E⦵ values become less negative, the reactivity to undergo oxidation (lose electrons) becomes less

What colour does Cr₂O₇²⁻ (aq) form?

Orange colour

What colour does Cr³⁺ (aq) have?

Green colour

Show the full equation of the reduction of Cr₂O₇²⁻ with zinc and a second equation when excess zinc is used. What colour change occurs?

Cr₂O₇²⁻ is orange

Cr³⁺ has a green colour

However Cr²⁺ has a pale blue colour

What can be used to oxidise Cr³⁺ to CrO₄²⁻?

Hydrogen peroxide