Metals (SQA National 5 Chemistry): Flashcards

A simple reactivity series can be established by adding equal-sized pieces of different metals to separate test tubes of the same dilute acid and comparing the rate of fizzing — faster fizzing indicates greater reactivity.

When a metal reacts with a dilute acid, the gas produced is hydrogen, which can be detected by holding a lit splint at the mouth of the test tube — it produces a squeaky pop.

False.

Only metals above hydrogen in the Electrochemical Series react with dilute acids. Metals below hydrogen, such as copper, do not react.

1. Metal + oxygen → metal oxide

2. Metal + water → metal hydroxide + hydrogen

3. Metal + acid → salt + hydrogen

Only the most reactive metals, such as lithium, sodium and potassium, react with cold water. The products are a metal hydroxide and hydrogen gas.

The excess method is a practical procedure in which more solid reactant (metal) is added than needed to ensure all of the acid is completely used up, preventing the final salt from being contaminated with unreacted acid.

To prepare a soluble salt from a metal and dilute acid, the three steps are: react the metal in excess with warm acid, then filter to remove the excess metal, then evaporate to obtain pure salt crystals.

False.

Copper is below hydrogen in the Electrochemical Series and does not react with dilute acids. Only metals above hydrogen, such as magnesium, zinc or iron, can be used.

The metal is added in excess to ensure that all of the acid is completely used up. This prevents the final salt from being contaminated with unreacted acid, and any leftover solid metal can then be removed by filtration.

Oxidation is a reaction in which an element, ion or compound loses electrons.

Reduction is a reaction in which an element, ion or compound gains electrons.

False.

Oxidation and reduction always occur simultaneously. When one substance loses electrons (is oxidised), another must gain them (is reduced) — this is why they are called redox reactions.

The mnemonic OILRIG stands for: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).

Magnesium is oxidised — it loses 2 electrons to form Mg²⁺. Copper(II) ions are reduced — each Cu²⁺ gains 2 electrons to form a neutral copper atom.

The substance higher in the Electrochemical Series is oxidised — its ion-electron equation is reversed. The substance lower in the series is reduced — its ion-electron equation is used as written.

When combining ion-electron equations to form an overall redox equation, the number of electrons lost must equal the number of electrons gained, and the electrons are then cancelled from both sides.

False.

The final overall redox equation must not include electrons. The ion-electron equations must be scaled so that the number of electrons lost equals the number gained, allowing them to cancel completely.

The equations must be multiplied so that the number of electrons lost in the oxidation half-equation equals the number of electrons gained in the reduction half-equation. If these numbers differ, they are scaled to the lowest common multiple before combining.

An ore is a rock that contains enough of a metal compound to make extraction of the metal economically worthwhile.

In an ore, the metal exists as a positive ion. To obtain the pure metal, these positive ions must gain electrons to become neutral metal atoms — gaining electrons is reduction.

True.

Very reactive metals form very stable compounds that are difficult to break down. This means more energy is required to extract them, which is why the most reactive metals must be extracted by electrolysis.

1. Heat alone — least reactive metals (low in the series), e.g. silver, gold and mercury

2. Heating with carbon or carbon monoxide — middle of the series, e.g. zinc, iron, lead and copper

3. Electrolysis — most reactive metals (high in the series), e.g. potassium, sodium, calcium, magnesium and aluminium

Metals such as silver, gold and mercury can be extracted by heat alone because their compounds are unstable and easily decompose.

A reducing agent is a substance that removes oxygen from a metal compound during extraction. Carbon (coke) and carbon monoxide are common reducing agents used to extract metals in the middle of the electrochemical series.

The most reactive metals form very stable compounds that cannot be reduced by carbon. Electrolysis uses a powerful direct electric current to break down the compound, providing enough energy to extract these metals — though this makes the process very expensive.

False.

Iron is extracted by heating its ore with a reducing agent (carbon monoxide) in a blast furnace. Electrolysis is reserved for the most reactive metals, such as aluminium, sodium and potassium.

In the extraction of aluminium by electrolysis, the positive Al³⁺ ions are attracted to the negative electrode, where each ion gains three electrons to become a neutral aluminium atom.

Electrolysis is the process of breaking down an ionic compound into its elements using electricity.

Electrolysis requires ions that are free to move. In solid ionic compounds the ions are fixed in a lattice and cannot carry charge through the electrolyte.

An electrolyte is a molten ionic compound or ionic solution in which the ions are free to move and can therefore conduct electricity.

False.

Positive ions are attracted to the negative electrode (cathode). Opposite charges attract.

At the negative electrode, positive ions gain electrons. This process is called reduction.

Direct current (DC) must be used because it causes ions to move consistently in one direction — positive ions towards the negative electrode and negative ions towards the positive electrode.

False.

Oxidation (loss of electrons) occurs at the positive electrode (anode). Reduction (gain of electrons) occurs at the negative electrode (cathode).

The three essential components are:

1. An electrolyte (molten or dissolved ionic compound)

2. Two electrodes (conductive rods placed in the electrolyte)

3. A direct current (DC) power supply

During electrolysis, negative ions are attracted to the positive electrode, where they lose electrons in a process called oxidation.

An electrochemical cell is a device that converts chemical energy into electrical energy by using a chemical reaction to produce a voltage.

A simple electrochemical cell requires two different metals placed in an electrolyte and connected by a wire through a voltmeter.

False.

The ion bridge allows ions to flow between the two solutions. Electrons flow through the external wire connecting the two metal electrodes.

A half-cell is a metal rod placed in a solution containing its own ions, used as one part of a complete electrochemical cell.

In a half-cell system, the two half-cells are connected by a wire and voltmeter to allow electrons to flow, and an ion bridge to allow ions to flow.

The ion bridge completes the circuit by allowing ions to move between the two half-cells. Without it, charge would build up in each beaker and the flow of electricity would stop.

A graphite rod is used because graphite is both unreactive and able to conduct electricity, providing a suitable surface for the electrode reaction without taking part in it.

False.

A cell can produce a voltage with a non-metal half-cell. A graphite rod is used as the electrode in place of a metal rod.

In an electrochemical cell, electrons always flow from the substance higher in the electrochemical series to the substance lower in the series.

Two examples of electrolytes are:

1. Salt water

2. Ammonium chloride solution

The electrochemical series is a list of elements and ions arranged in order of their ability to gain or lose electrons, used to predict electron flow and voltage in electrochemical cells.

The further apart the two substances are in the electrochemical series, the larger the voltage the cell will produce.

False.

Electrons always flow from the substance higher in the electrochemical series to the substance lower down. The higher substance is oxidised and loses electrons.

The substance higher in the electrochemical series undergoes oxidation and its electrode gets smaller over time.

The copper electrode undergoes reduction because copper is lower in the electrochemical series. Copper ions gain electrons and the electrode gets larger as copper plates out.

The five steps are:

1. Identify which substance is oxidised (higher in series) and which is reduced (lower)

2. Write the two ion-electron equations, reversing the equation for the oxidised substance

3. Balance the electrons so that loss equals gain

4. Combine the equations

5. Cancel the electrons from both sides

True.

Electrons cannot be created or destroyed. If the numbers do not balance, one or both equations must be multiplied until they are equal before the equations are combined.

When writing the ion-electron equation for the substance that is higher in the electrochemical series, the equation from the data booklet must be reversed.

The overall redox equation is Zn (s) + Cu²⁺ (aq) → Zn²⁺ (aq) + Cu (s).

Zinc is oxidised (higher in the series) and copper(II) ions are reduced.

Aluminium loses 3 electrons per atom and iron(II) gains 2 electrons per ion. To balance, the aluminium equation is multiplied by 2 and the iron(II) equation by 3, giving 6 electrons transferred on each side.