developing metals (DM) Flashcards
What is oxidation in terms of electron transfer?
Oxidation is the loss of electrons.
What is reduction in terms of electron transfer?
Reduction is the gain of electrons.
What role do reducing agents play in redox reactions?
Reducing agents donate electrons to reduce another substance.
What role do oxidising agents play in redox reactions?
Oxidising agents take electrons away from other substances, becoming reduced in the process.
How do you balance redox equations?
Use H+, H2O, and e- to balance the redox equations.
What is the purpose of an acid-base titration?
It is used to determine the exact amount of acid needed to neutralise a known quantity of alkali.
What indicator is typically used in acid-base titrations, and what color change does it show?
Phenolphthalein is used, and it changes from colorless to pink.
What is the goal of a redox titration?
A redox titration is used to determine how much oxidising agent is required to completely react with a known amount of reducing agent.
Why is dilute sulfuric acid added in redox titrations?
It ensures there are plenty of H+ ions to facilitate the reduction of the oxidising agent.
What are electrochemical cells, and how do they work?
Electrochemical cells consist of two different metals dipped in salt solutions of their own ions, connected by a wire and a salt bridge. Oxidation occurs at the negative electrode, and reduction happens at the positive electrode. Electrons flow through the wire from the more reactive metal to the less reactive one.
In a zinc/copper electrochemical cell, what happens at each electrode?
Zinc is oxidized to Zn2+ (s) –> Zn2+ (aq) + 2e- at the negative electrode, and copper ions (Cu2+) are reduced to solid copper (Cu) at the positive electrode: Cu2+(aq) + 2e- –> Cu(s).
How do you set up an electrochemical cell?
Clean electrodes with emery paper, remove grease using propanone, then connect them with a salt bridge made of filter paper soaked in salt solution, such as KCl.
What is electrode potential?
Electrode potential is the potential difference between two half-cells that drives electron movement. A more negative electrode potential means the substance is more easily oxidized (acts as a reducing agent).
What is the standard hydrogen electrode (SHE)?
The SHE is the reference electrode used in electrochemical cells, assigned a value of 0.00V. It has 1 mol/dm³ solutions, 298K (25°C) temperature, and 100 kPa pressure.
How do you calculate the electrode potential of a cell?
The electrode potential of a cell is calculated as (E more +ve) - (E more -ve), and the value is always positive.
What does a more reactive metal indicate about its electrode potential?
A more reactive metal has a more negative electrode potential, meaning it loses electrons more easily.
What does a more reactive non-metal indicate about its electrode potential?
A more reactive non-metal has a more positive electrode potential, meaning it gains electrons more easily.
How can the electrochemical series be used?
The electrochemical series predicts whether a reaction is feasible by comparing the electrode potentials of the substances involved.
What is rusting, and what are the products formed?
Rusting is the corrosion of iron when exposed to oxygen and water, leading to the formation of iron (II) hydroxide, which is further oxidized to iron (III) hydroxide.
How can rusting be prevented?
Rusting can be prevented by painting, greasing, or using the sacrificial method (zinc), which has a more negative electrode potential than iron.
What is a transition metal?
A transition metal is a d-block element that can form at least one stable ion with an incomplete d sub-shell.
What is the electron configuration rule for transition metals when ionizing?
Transition metals fill the 4s subshell before the 3d subshell and lose 4s electrons first when ionizing.
What is the exception for chromium’s electron configuration?
Chromium has one electron in each orbital of the 3d subshell and one electron in the 4s subshell, which makes it more stable.
What is the exception for copper’s electron configuration?
Copper prefers a full 3d subshell and just one electron in 4s, which is more stable.
Why is scandium not considered a transition metal?
Scandium only forms Sc3+, which has an empty d subshell.
Why is zinc not considered a transition metal?
Zinc only forms Zn2+, which has a full d subshell.
What are the key properties of transition metals?
Transition metals have variable oxidation states, form colored ions in solution, and have closely spaced energy levels in the 4s and 3d orbitals, allowing them to gain or lose electrons in various oxidation states.
What is a complex ion?
A complex ion is a central metal ion bonded to ligands via coordinate bonds.
What is a coordinate (dative) bond?
A coordinate bond is formed when a ligand donates a pair of electrons to the central metal ion.
What is a ligand?
A ligand is an atom, ion, or molecule that donates a pair of electrons to form a coordinate bond with a central metal ion. Monodentate ligands donate one lone pair, while bidentate ligands donate two lone pairs.
What is the coordination number?
The coordination number is the number of coordinate bonds formed between a central metal ion and its surrounding ligands.
What shapes can complex ions with 4 coordinate bonds take?
Complex ions with 4 coordinate bonds usually have a tetrahedral shape, but can sometimes be square planar (e.g., cisplatin).
How do ligands affect the 3d subshell of the central metal ion?
Ligands split the 3d subshell into two energy levels. Electrons can absorb energy to jump to higher orbitals, and the size of the energy gap depends on factors like the central metal ion, oxidation state, ligands, and coordination number.
Why do transition metal compounds have color?
Transition metal compounds have color because the 3d electrons absorb specific wavelengths of light as they jump between energy levels in the presence of ligands.
What are the colors of some transition metal hydroxides when reacted with NaOH?
Copper: Pale blue to dark blue precipitate; Iron (II): Pale green to dark green; Iron (III): Yellow to orange.
What is ligand substitution, and what is its effect on transition metal complexes?
Ligand substitution involves replacing one ligand with another, often resulting in a color change.
How do transition metal catalysts work?
Transition metals act as catalysts by changing their oxidation states, transferring electrons, and speeding up reactions at lower temperatures and pressures.
What is the process of heterogeneous catalysis?
In heterogeneous catalysis, molecules are adsorbed onto the catalyst surface, bonds are weakened, reactions occur, and products desorb from the catalyst.
What makes a good heterogeneous catalyst?
A good heterogeneous catalyst has a strong enough attraction to hold molecules long enough to react but not so strong that it prevents desorption and blocks new reactants.
How do transition metals work as homogeneous catalysts?
In homogeneous catalysis, the catalyst forms an intermediate, and the activation energy for the reaction with the intermediate is lower than that for direct reactant-to-product conversion.
What is colorimetry, and how is it used?
Colorimetry measures the absorbance of light by a solution. The absorbance is used to determine the concentration of a substance, especially transition metal ions, by using a color filter and comparing absorbances to a calibration graph.
How is a calibration graph used in colorimetry?
A calibration graph plots absorbance versus known concentrations. It allows you to find the concentration of an unknown substance by comparing its absorbance to the graph.
What is visible spectroscopy, and how does it relate to transition metal complexes?
Visible spectroscopy measures light absorption by a solution and can be used to identify transition metal complexes based on their unique absorption spectra, which result from transitions between 3d orbitals.
