C5
Relate the products of electrolysis to the electrolyte and electrodes used, exemplified by the specific examples in the Core together with aqueous copper(II) sulfate using carbon electrodes and using copper electrodes (as used in the refining of copper).
During electrolysis the electrons move from the power supply towards the cathode. - Positive ions within the electrolyte move towards the negatively charged electrode which is the cathode. Here they accept electrons from the cathode and either a metal or hydrogen gas is produced.
Define electrolysis as the breakdown of an ionic compound when molten or in aqueous solution by the passage of electricity.
Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them. Electricity is the flow of electrons or ions. For electrolysis to work, the compound must contain ions. Electrolysis is the process of decomposing (breaking down) an ionic substance, called an electrolyte, into simpler substances using electricity. During electrolysis, positively charged ions (cations) move to the negative electrode (cathode) , and negatively charged ions (anions) move to the positive electrode (anode). Ions are discharged at the electrodes producing elements.
Describe electrolysis in terms of the ions present and the reactions at the electrodes, in terms of gain of electrons by cations and loss of electrons by anions to form atoms.
Electrolysis of water is the decomposition of water (H2O) into oxygen (O2) and hydrogen gas (H2) due to an electric current being passed through the water. Electrolysis is a process by which electric current is passed through a substance to effect a chemical change. The chemical change is one in which the substance loses or gains an electron (oxidation or reduction). Electrolysis can be used to separate a substance into its original components/elements and it was through this process that a number of elements have been discovered and are still produced in today's industry. Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them. Electricity is the flow of electrons or ions. It is also called water splitting. It requires a minimum potential difference of 1.23 volts to split water.
Predict the products of the electrolysis of a specified molten binary compound.
Of molten ionic compounds: a metal is formed at the cathode and a non-metal at the anode. It's fairly simple to predict these results. Of aqueous solutions: H and OH ions are present in aqueous solutions along with the metal/non-metal ions. The ions with the lower reactivity will be discharged at their respective electrodes.When aqueous solutions of acids are electrolysed, oxygen is formed at the anode and hydrogen is formed at the cathode.
Define and identify an oxidising agent as a substance which oxidises another substance during a redox reaction and a reducing agent as a substance which reduces another substance during a redox reaction.
The oxidizing agent is a substance that tends to bring about oxidation by being reduced and gaining electrons. It is normally a non-metal or positive ion. cause oxidation reactions to take place. gains electrons from other atoms or ions (is itself reduced). The reducing agent is a substance that tends to bring about reduction by being oxidized and losing electrons. A reducing agent is typically in one of its lower possible oxidation states, and is known as the electron donor. A reducing agent is oxidized, because it loses electrons in the redox reaction. The oxidizing agent is also known as the oxidant and the reducing agent is known as the reductant.
Deduce an order of reactivity from a given set of experimental results.
When displacement reaction equations is given, you should be able to put them in order of reactivity. Just remember that the metal that displaces the other one is the more reactive one. In a reactivity series, the most reactive element is placed at the top and the least reactive element at the bottom. More reactive metals have a greater tendency to lose electrons and form positive ions. We can use the reactions of metals with acids to tell us how reactive that metal is. The more vigorously it reacts, the more reactive the metal. The slower the reaction (sometimes there is no reaction at all), the less reactive the metal. - Reactive metals (such as potassium, sodium, lithium and calcium) will react rapidly in cold water - Less reactive metals (such as magnesium, zinc and iron) won't react with cold water but will react with water vapour (steam) - Unreactive metals (such as copper, silver and gold) won't react with either cold water or steam
Define redox in terms of electron transfer, and identify such reactions from given information, which could include simple equations.
A chemical reaction that takes place between an oxidizing substance and a reducing substance (A redox reaction is defined as a reaction in which oxidation and reduction take place simultaneously). The oxidizing substance loses electrons in the reaction, and the reducing substance gains electrons. Within the reaction, contains the oxidizing agent and reduction agent. The oxidizing agent is a substance that tends to bring about oxidation by being reduced and gaining electrons. It is normally a non-metal or positive ion. cause oxidation reactions to take place. gains electrons from other atoms or ions (is itself reduced). The reducing agent is a substance that tends to bring about reduction by being oxidized and losing electrons. A reducing agent is typically in one of its lower possible oxidation states, and is known as the electron donor. A reducing agent is oxidized, because it loses electrons in the redox reaction. The oxidizing agent is also known as the oxidant and the reducing agent is known as the reductant. Redox reactions are comprised of two parts, a reduced half and an oxidized half, that always occur together. The reduced half loses oxygen, gains electrons, oxidation number decreases and gains hydrogen, while the oxidized half gains oxygen, loses electrons, oxidation number increases and loses hydrogen. A spectator ion is an ion that does not participate in the chemical change in a reaction. To identify these spectator ions, we'll first have to write out the ionic form of all the chemical species involved in this reaction. Spectator ions help to carry out the reaction and transfer electrons, but do not take part within the reaction.
Describe oxidation and reduction in chemical reaction in terms of oxygen loss/gain (Oxidation state limited to its use to name ions, e.g. iron(II), iron(III), copper(II).)
A chemical reaction that takes place when a substance comes into contact with oxygen or another oxidizing substance. Oxidation is gain of oxygen, loss of electrons, Gain in oxidation number/state or loss of hydrogen. Oxygen is gained by the substance through the reaction between the substance and oxygen. In a chemical reaction, the electrons are either gained or lost by an atom. The gain of the electrons is known as reduction, whereas the loss of electrons is known as oxidation. Generally, one atom loses the electron (s) and gets oxidized, which electron is then gained by another atom to get reduced. Oxidation state is a number assigned to an element in chemical combination which represents the number of electrons lost (or gained, if the number is negative), by an atom of that element in the compound. oxidation number, also called oxidation state, the total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom. A loss of negatively-charged electrons corresponds to an increase in oxidation number, while a gain of electrons corresponds to a decrease in oxidation number. Therefore, the element or ion that is oxidized undergoes an increase in oxidation number. Oxidation is a process where a substance: Loses one or more electrons. Gains an oxygen atom or Electronegative atoms. Loses a hydrogen atom or Electropositive atoms. Rusting is an example of oxidation. Chemistry (Single Science) Reduction is the transfer of electrons between species/substances in a chemical reaction where there is a process of gaining electrons or a decrease in the oxidation state by an element. It occurs when the noble substance undergoes a reduction in oxygen or reacts with another reducting substance. A reduction chemical reaction involves increasing electrons associated with a single atom or a group of atoms. Reduction is the loss of oxygen, gain of electrons, loss of oxidation state.number or gain or hydrogen. Reduction is the loss of oxygen atom from a molecule or the gaining of one or more electrons. A reduction reaction is seen from the point of view of the molecule being reduced, as when one molecule gets reduced another gets oxidised. The oxygen reacts with the less noble substance. Reduction involves a half-reaction in which a chemical species decreases its oxidation number, usually by gaining electrons. The other half of the reaction involves oxidation, in which electrons are lost. Electrons are gained as when the oxidising substance undergoes oxidation, it's electrons are transferred to the oxidant to have a neutral charge. Oxidation: - The gain oxygen - The loss of electrons - The gain in oxidation state - The loss of hydrogen Reduction: - The loss of oxygen - The gain of electrons - The loss in oxidation state - The gain in hydrogen
Describe the electroplating with copper.
Electroplating is basically the process of plating a metal onto the other by hydrolysis mostly to prevent corrosion of metal or for decorative purposes. The process uses an electric current to reduce dissolved metal cations to develop a lean coherent metal coating on the electrode. Copper is an excellent conductor of electricity, so you can use copper electroplating to improve the conductivity of a base material. Copper is also highly malleable, making it ideal for components that bend, and offers good protection against corrosion. The concept of copper electroplating is straightforward: Submerge the wafer to be plated into an electrolyte bath, apply a current, and copper ions will migrate and deposit onto regions with a pre-existing metal seed layer. During electroplating with copper, copper metal gets transferred from positive electrode to the negative electrode. electroplating is the alligning up of another metal upon a metal. This is done with the help of a electroplating contraption which contains a brine solution, a battery, some wires, and alligator clips which hold carbon rods attached with the metal to be electroplated and the metal which has to be layered.
Use the terms inert electrode, electrolyte, anode and cathode.
Inert: An inert chemical substance is one that is not generally reactive. This is a synonym for "inactive" with respect to chemical reactions. Electrode: An electrode is a metal whose surface serves as the location where oxidation-reduction equilibrium is established between the metal and what is in the solution. The electrode can either be an anode or a cathode. An anode receives current or electrons from the electrolyte mixture, thus becoming oxidized. It is a conductor used to establish electrical contact with a nonmetallic part of a circuit. It is an element in a semiconductor device (such as a transistor) that emits or collects electrons or holes or controls their movements.The electrode is the place where electron transfer occurs. An electrode is classified as either a cathode or an anode depending on the type of chemical reaction that occurs. If an oxidation reaction occurs at an electrode (oxidation being the loss of electrons), then the electrode is classified as an anode. Anode: The positively charged electrode in electrolysis is called the anode . Negatively charged ions move towards the anode. The Anode is the negative or reducing electrode that releases electrons to the external circuit and oxidizes during and electrochemical reaction. The Cathode is the positive or oxidizing electrode that acquires electrons from the external circuit and is reduced during the electrochemical reaction. The anode is the electrode where electricity moves into. The cathode is the electrode where electricity is given out or flows out. The anode is usually the positive side. A cathode is a negative side. It acts as an electron donor. Cathode: The Cathode is the positive or oxidizing electrode that acquires electrons from the external circuit and is reduced during the electrochemical reaction. The Electrolyte is the medium that provides the ion transport mechanism between the cathode and anode of a cell. The cathode is the electrode where electricity is given out or flows out. The anode is usually the positive side. A cathode is a negative side. It acts as an electron donor. A cathode is the metallic electrode through which current flows out in a polarized electrical device. Conversely, an anode is the electrode in a polarized electrical device through which current flows in from an outside circuit. Electrolyte: A substance that breaks up into ions (particles with electrical charges) when it is dissolved in water or body fluids. Some examples of ions are sodium, potassium, calcium, chloride, and phosphate. a substance (as an acid or salt) that when dissolved (as in water) conducts an electric current. 2 : a substance (as sodium or calcium) that is an ion in the body regulating the flow of nutrients into and waste products out of cells.
Describe and explain barrier methods of rust prevention, including paint and other coatings.
Iron rusts when it comes into contact with both air and water. Water reacts with the iron over time and the oxygen in the air oxidises the iron. Combined, this forms a layer of rust. 4Fe(s) + 3O2(g) + 2H2O(l) ———-> 2Fe2O2.H2O(s) There are several ways to prevent rust from forming: Coatings are designed to prevent oxidation by keeping the part from exposure to oxygen and water. - Paint the surface: By painting an iron object, iron does not come in contact with atmospheric oxygen and moisture directly. This prevents rusting. - Covering the surface in plastic: Plastic is cheap and acts as a cover for the iron, for instance, it stops water or oxygen reaching the metal surface. - Metal plating (through electroplating): Electroplating is the process of using electrodeposition to coat an object in a layer of metal(s). Engineers use controlled electrolysis to transfer the desired metal coating from an anode (a part containing the metal that will be used as the plating) to a cathode (the part to be plated). Electroplating entails the electrodeposition of a metal onto the surface of a steel or iron product. This metal coating acts as a sacrificial barrier that can slow and even prevent corrosion from forming on the underlying material, which is referred to as the substrate. - Greasing and oiling the surface from time to time: When metal is coated in oil it forms a protective barrier that stops any external elements from seeping through. This includes water. As H2O is unable to penetrate the metal, the rusting process doesn't start. As well as tangible water, oil also repels the water that's present in oxygen. - Zinc galvanising: coating the iron/steel with zinc; the zinc will react with the oxygen rather than iron because it is more reactive. Using a more reactive metals to protect a less reactive metal from corrosion is called sacrificial protection.
State the general principle that metals or hydrogen are formed at the negative electrode (cathode), and that non-metals (other than hydrogen) are formed at the positive electrode (anode).
Positive ions are attracted to the cathode, where they pick up one or more electrons and are discharged. Either the metal is deposited or you get hydrogen produced from the water. Due the polarity of the electrodes, metals and hydrogen gas will form at the cathode. This is because metal ions and hydrogen ions are positive and are attracted to the negative cathode. Non-metal ions are negative in charge and are, therefore, attracted to the positive anode of the cell. Whether hydrogen or a metal is produced at the cathode depends on the position of the metal in the metal reactivity series : the metal is produced at the cathode if it is less reactive than hydrogen. hydrogen is produced at the cathode if the metal is more reactive than hydrogen. Opposite charges attract each other while like charges repel each other. As a result during electrolysis , the negative part that is oxygen is attracted towards the positive electrode, i.e. the anode, while the positive part, that is hydrogen, is attracted towards the negative electrode, i.e. the cathode negative non-metal ions are attracted to the positive electrode, where they lose electrons and form non-metal atoms. Non-metal ions are negative in charge and are, therefore, attracted to the positive anode of the cell.
Place in order of reactivity: potassium, sodium, calcium, magnesium, aluminium, (carbon), zinc, iron, (hydrogen) and copper, by reference to the reactions, if any, of the elements with: ㄧ water or steam ㄧ dilute hydrochloric acid ㄧ reduction of their oxides with carbon.
Potassium Sodium Lithium Calcium Magnesium Aluminium Carbon Zinc Iron Lead Hydrogen Copper Silver Gold Perhaps Some Lively Cows May All Come Zooming In Large Herds Chewing Some Grass
Describe the reactivity series in terms of the tendency of a metal to form its positive ion, illustrated by its reaction, if any, with: ㄧ aqueous ions of other listed metals ㄧ the oxides of the other listed metals.
Previosuly, we saw that a more reactive halogen will replace a less reactive halogen in a metal halide. We can see this is a competition to see which halogen combines best with the metal. We call this type of a reaction a displacement reaction. Metals can also 'compete' in a similar way. Iron(III) oxide + aluminium ———-> iron + aluminium oxide In the above, reaction the aluminium displaced the iron (think of it as 'the aluminium stole the oxide and the iron was left alone'). This happened because aluminium is higher in the reactivity series than iron i.e. aluminium is more reactive than iron. Let's take another example, with an aqueous solution, and see how the metal ions form: zinc + Copper(II)sulfate ———-> zinc sulfate + copper Zn(s) + CoSO4(aq) ———————> ZnSO4(aq) + Cu(s) Here, the zinc, being the more reactive metal, has clearly displaced copper to form zinc sulfate Let's break it up into half equations: Zn(s) - 2e- ———-> Zn2+(aq) the zinc oxidised (lost electrons) Cu2+(aq) + 2e- ———-> Cu(s) the copper reduced (gained electrons) We can see that the more reactive metal, zinc, has lost electrons and the less reactive metal, copper, has gained electrons. The more reactive a metal is, the more easily it loses its valence electrons. It is easier to lose valence electrons and thus be more reactive, if: the valence electrons are further away from the nucleus. When they are farther away, the attraction of these electrons (negative charge) to the protons (positive charge)in the nucleus will be reduced. So it is easier to 'let go' of the electrons. there are more electron shells between the nucleus and the valence electrons. These shells shield the valence electrons from the charge of the nucleus (protons). there are fewer protons in the nucleus (less charge) to pull the electrons towards them Zinc is more reactive than copper because its valence electrons are farther away from the nucleus and it has more shells. Zinc has more protons than copper but the other two conditions outweigh this one. So overall, zinc finds it easier to lose its valence electrons than copper, and so is more reactive, and thus can displace copper.
State the conditions required for the rusting of iron (presence of oxygen and water).
Rust is the term we use to describe red iron oxides produced when ferrous metals corrode. Rust is also known as iron oxide and corrosion. This chemical compound comes in many different combinations of iron and oxygen. Rust is the common name for a very common compound, iron oxide. Iron oxide, the chemical Fe2O3, is common because iron combines very readily with oxygen -- so readily, in fact, that pure iron is only rarely found in nature. Rusting is an oxidation reaction. The iron reacts with water and oxygen to form hydrated iron(III) oxide, which we see as rust. The word equation for the reaction: iron + water + oxygen → hydrated iron(III) oxide. Iron rusts when it comes into contact with both air and water. Water reacts with the iron over time and the oxygen in the air oxidises the iron. Combined, this forms a layer of rust. The iron reacts with water and oxygen to form hydrated iron(III) oxide, which we see as rust. Iron and steel rust when they come into contact with water and oxygen - both are needed for rusting to occur. Iron when reacts with moist air forms a reddish brown layer of iron oxide which is known as rust. Iron when reacts with moist air forms a reddish brown layer of iron oxide which is known as rust.
Describe and explain sacrificial protection in terms of the reactivity series of metals and galvanising as a method of rust prevention.
Sacrificial protection: Sacrificial protection is a corrosion protection method in which a more electrochemically active metal is electrically attached to a less active metal. The highly active metal donates electrons to replace those which may have been lost during oxidation of the protected metal. The protection of iron or steel against corrosion by using a more reactive metal. A common form is galvanizing, in which the iron surface is coated with a layer of zinc. A sacrificial metal is a metal used as a sacrificial anode in cathodic protection that corrodes to prevent a primary metal from corrosion or rusting. It may also be used for galvanization. Sacrificial protection is the protection of iron or steel against corrosion by using a more reactive metal. Pieces of zinc or magnesium alloy are attached to pump bodies and pipes. The protected metal becomes the cathode and does not corrode. The anode corrodes, thereby providing the desired sacrificial protection. Galvanising: Galvanized coatings are formed by a chemical process during which steel and zinc metallurgically bond, forming a series of corrosion-inhibiting, highly abrasion-resistant zinc/iron alloy layers. Galvanizing is the process of applying zinc coating to a more noble metal (popularly steel or iron) to prevent corrosion (rusting). Hot-dip galvanization is the most well-known method in which the steel part is submerged in a bath of molten zinc. The process of galvanization is performed via hot-dipping and instantaneous annealing, which produces a matte gray finish. Galvannealed steel is a zinc-iron alloy product, where the base metal is coated by the hot-dip process, then heated to induce alloying between the molten zinc coating and the steel. The hot dip galvanizing process is relatively simple. It involves cleaning steel and immersing it in molten zinc to obtain a coating. Hot dip galvanizing is the process of coating iron or steel with a layer of zinc by immersing the metal in a bath of molten zinc at a temperature of around 450 °C (842 °F). How does it prevent rusting? Sacrificial protection: Iron can be protected from rusting if it is in contact with a more reactive metal, such as zinc. The more reactive metal oxidises more readily than iron, so it 'sacrifices' itself while the iron does not rust. Once the sacrificial metal has corroded away, it can simply be replaced. Sacrificial anodes are used to protect metal structures from corroding. Sacrificial anodes work by oxidizing more quickly than the metal it is protecting, being consumed completely before the other metal reacts with the electrolytes. Galvanising: Galvanizing protects from rust in a number of ways: It forms a barrier that prevents corrosive substances from reaching the underlying steel or iron. The zinc serves as a sacrificial anode so that even if the coating is scratched, the exposed steel will still be protected by the remaining zinc. Galvanising is a method of rust prevention. The iron or steel object is coated in a thin layer of zinc. This stops oxygen and water reaching the metal underneath - but the zinc also acts as a sacrificial metal . Zinc is more reactive than iron, so it oxidises in preference to the iron object.
Describe, in outline, the chemistry of the manufacture of: ー aluminium from pure aluminium oxide in molten cryolite, ー chlorine, hydrogen and sodium hydroxide from concentrated aqueous sodium chloride. (Starting materials and essential conditions should be given but not technical details or diagrams)
pure alluvium oxide is a white powder Aluminium from aluminium oxide in molten cryolite: Aluminum is extracted from aluminum oxide by a process called electrolysis. First of all, aluminum oxide needs to be in molten form to extract the aluminum ions. Aluminum oxide, however, has a high melting point. Therefore, aluminum oxide is dissolved in molten cryolite. Aluminium oxide is found in the mineral ore called bauxite. Bauxite is first crushed and mixed with sodium hydroxide. The aluminium oxide reacts with the sodium hydroxide and dissolves. Al2O3(s) + 2NaOH(aq) ———-> 2NaAlO2(aq) + H2O Sodium aluminate is formed (2NaAlO2). This is then heated to extract the aluminium oxide. Aluminium is extracted from aluminium oxide through electrolysis. The aluminium oxide needs to be molten first but it's melting point is too high (2040°C). So, the aluminium oxide is dissolved in molten cryolite (cryolite is the term for sodium aluminium flouride- Na3AlF6). Now, electrolysis can be carried out.Electrolysis is carried out using graphite (a form of carbon) electrodes. The cathode is the carbon lining on the steel tank. The anodes are all dipped into the cryolite from above. At the cathode, aluminium ions gain electrons (reduction) and are reduced to aluminium metal. Al3+ + 3e- ————> Al The liquid aluminium falls into the bottom of the cell. At the anode, the oxide ions lose electrons (oxidisation) and become oxygen. 2O2- - 4e- ————> O2 This oxygen react with the carbon anodes to form carbon-dioxide gas. Because the carbon anodes burn away due to this reaction, they need to be replaced from time to time. chlorine, hydrogen and sodium hydroxide from concentrated aqueous sodium chloride: When an electric current is passed through concentrated sodium chloride solution, hydrogen gas forms at the negative electrode, chlorine gas forms at the positive electrode, and a solution of sodium hydroxide also forms. A concentrated aqueous solution of sodium chloride is called brine. The electrolysis of brine is used to produce chlorine, hydrogen and sodium hydroxide. The ions in the solution are Na+, H+, Cl- and OH-. At the anode, chloride ions lose electrons and is discharged as chlorine gas. (Chlorine is less reactive than hydroxide). 2Cl- (aq) - 2e-——-> Cl2(g) At the cathode, hydrogen ions gain electrons and hydrogen gas is discharged (Hydrogen is less reactive than sodium). 2H+(aq) + 2e- ————-> H2(g). The ions remaining in the solution are Na+ and OH-. So an aqueous solution of sodium hydroxide is formed!
