4.1 [Group 2]

Question 1

what is the definition of first ionisation energy?

Answer 1

First ionisation energy of an element is the energy required to remove an electron from each atom in one mole of atoms in the gaseous state.

Question 2

What is the definition of second ionisation energy?

Answer 2

Second ionisation energy of an element is the energy required to remove an electron from each singly charged positive ion in one mole of positive ions in the gaseous state.

Question 3

What are the trends for ionisation energy in the group 2 elements?

Answer 3

First and second ionisation energy decreases down the group, atomic radius increases down the group as well making it easier to remove electrons.

Question 4

What are the factors to consider when explaining trends in ionisation energy?

Answer 4

Nuclear charge (number of protons)
The orbital in which the electron exists
The shielding effect the repulsion between filler inner shells and electrons being removed.

Question 5

Why does Ionisation energy decrease down group 2?

Answer 5

As nuclear charge increases, so do the forces of attraction for the electron being removed also increases means an increase in ionisation down the group.

As each quantum shell is added, energy of the outermost electron increases.

As the number of filled inner shells increases, the forces of repulsion on the electron being removed increases meaning a decrease in ionisation energy down the group.
One of the factor causes an increase two causes a decrease the combined effect of the last 2 factors outweighs the effect of the first factor explaining a decrease down the group.

Question 6

What are the basic trends in reactivity for group 2 elements?

Answer 6

In all of these reactions element changes into an M2+ ion, there is a general increase in reactivity down the group. This can be explained by the decrease in energy needed to remove the 2 electrons from each atom of the element.

Question 6

What happens when Magnesium burns in oxygen?

Answer 6

Burns with a bright white flame

Question 7

What are the reactions with Group 2 elements in the air?

Answer 7

When calcium, strontium and barium are heated in air, the reactions are more vigerous. This may be hard to see if the reactions are not fresh samples.
Elements need to be heated for reaction to start, without heating slow reaction between eement and oxygen when exposed to air. This forms a surface coating of oxide helps prevents the element from further reactions.

Barium most reactive stored in oil to stop it reacting with oxygen.
Metal oxide formed

Question 8

How do Group 2 elements react with chlorine?

Answer 8

Group 2 elements combine with chlorine when heated in the gas. Just like reactions with oxygen the reactions with chlorine become more vigorous down the group, although this is harder to see.
General equation for the reactions
M + Cl2 > MCl2
Products are M2+ and Cl-

Question 9

How do Group 2 elements react with water?

Answer 9

Reaction between Magnesium and water is very slow and does not proceed completely. Calcium, Strontium and barium react with increasing vigour, which can be seen by increase in effervescence.
General equation for this reaction is:
M + 2H20 > M(OH)2 + H2
Products are hydrogen gas and hydroxides containing M2+ and OH- ions

Question 9

How does Calcium react with water?

Answer 9

Calcium hydroxide is only slightly soluble in water so the liquid in this experiment goes cloudy as a precipitate of calcium hydroxide forms.
Ca + 2H20 > Ca(OH)2 + H2

Question 10

How does Magnesium react with steam?

Answer 10

Magnesium reacts differently when heated in stem - It rapidly forms magnesium oxide (white solid) hydrogen gas in a vigerous reaction. Equation for this reaction
Mg + H2O > MgO + H2

Hydrogen formed burned it leaves the tube. This is for safety reasons prevent the escape of highly flammable gas into the laboratory.

Question 11

What are the reactions of Group 2 oxides with water?

Answer 11

The Group 2 oxides are classes as basic oxides. Which means they can react with water to form alkalis. These reactions occur when oxides are added to water. Only observation is that the solid react to form a colourless solution.
General equation:
MO + H20 > m(OH)2
Hydroxide ions are formed which shows the solution as alkaline.

Question 12

What are Basic Oxides?

Answer 12

Basic Oxides are oxides of metals that react with water to form metal hydroxides, and with acids to form salts and water.

Question 13

What are the trends in solubility of the hydroxides?

Answer 13

The pH value of the alkaline solution formed depends partly on the relative amounts of oxide and water, but is also affected by the differences in solubility of the hydroxides.
When MgO reacts with water the Magnesium hydroxide formed has a low solubility in water. The solubility of the Group 2 hydroxides increase down the group. Therefore, the maximum alkalinity of the solutions formed increase down the group.

Question 14

What is the test for carbon dioxide?

Answer 14

Limewater is needed for the test of CO2. The limewater goes cloudy as a white precipitate forms. Limewater is the name used for a saturate aqueous solution of Calcium Hydroxide. Carbon dioxide reacts to form Calcium carbonate which is insoluble in water and is the white precipitate.
CO2 + Ca(OH)2 > CaCO3 + H2O

Question 15

What is Milk of Magnesia?

Answer 15

Indigestion remedy called Milk of Magnesia. Contains a standard solution of Magnesium Hydroxide mixed with extra solid Magnesium hydroxide acts as a anti-acid.
Human stomach contains HCl to digest food, sometimes if there is too much can cause indigestion. Taking milk of Magnesia neutralises some of the HCl and relieves the symptoms.
Mg(OH)2 + 2HCl > MgCl2 + 2H20
Although Hydroxide ions attack human tissue, very low solubility of Magnesium hydroxide means the concentration of OH ions in the medicine is very low cannot affect health.

Question 16

How do the Group 2 Oxides and Hydroxides react with acids?

Answer 16

All of the G2 oxides and Hydroxides react with acids to form salts and water. Described as neutralisations reactions.
During the reactions the only observations made are that a white solid reacts to form a colourless solution. The reactions are endothermic so may use to measure enthalpy change.
Mgo + H2SO3 > MgSO4 + H20

Question 17

How have farmers used Calcium hydroxides in agriculture?

Answer 17

For centuries, farmers have used lime to control soil acidity so that a greater yield of crops can be obtained.
Lime is mostly calcium hydroxide obtained from limestone, and neutralises excess acidity in the soil. Using nitric acid to represent the acid in the soil

Ca(OH)2 + 2HNO3 > Ca(NO3)2 + 2H2O

Question 18

What are the trends in solubility of the Group 2 sulfates ?

Answer 18

All G2 nitrates and chlorides are soluble, but the solubility of G2 sulfates decreases down the group
Magnesium sulfate is classed as soluble
Calcium sulfate is slightly soluble
Strontium sulfate and barium sulfate are insoluble.

Solubility increases down the group meaning Magnesium hydroxide is the least soluble and Barium being the most. Magnesium can be used as medicine as it can neutralise acids.

Question 19

What is the test for Sulfate ions?

Answer 19

The presence of sulfate ions in aqueous solution can be shown by adding a solution containing barium ions ( barium nitrate or chloride). Any sulfate ions will react with added barium ions to form a white precipitate of barium sulfate.
Ba2+ + SO4 2- > BaSO4

There are other anions that form a white precipitate with Barium ions, like carbonate ions. So in the test there must be H+ ions present to prevent Barium carbonate forming as a white precipitate. Dilute Nitric acid or Hydrochloric acid is therefore added as part of the test

Question 20

How would you test for the presence of Sulfate ions in a solution of sodium sulfate?

Answer 20

Add dilute nitric acid and barium nitrate solution, a white precipitate will form.
Ba(NO)3 + Na2SO4 > BaSO4 + 2NaNO3

Question 21

What are Barium meals?

Answer 21

Barium is poisonous to humans however barium sulfate is used in hospitals this is because it is insoluble although containing barium ions these ions are not free to move. Allows soft tissue to be seen more easily on X-rays

Question 22

What is the definition of thermal stability?

Answer 22

Thermal Stability is a term that indicates how stable a compound is when it is heated. Does it decompose at all (very thermally stable) or does it decompose as much as possible ( not at all thermally stable).

Question 23

How do Group 2 nitrates and carbonates thermally decompose compared to Group 1?

Answer 23

Group 2 carbonates and nitrates are very different compared to Group 1 when heated the reasons for this are: 1.The charge on a Group 2 cation is double of that on a Group 1 cation. 2.The ionic radius of a Group2 ion is smaller than that of a Group 1 cation in the same period. 3.The nitrate and carbonate anions are more complex than the CL- ion.

Question 24

What are the explanations for why Group 2 carbonates and nitrates thermally decompose?

Answer 24

The larger more complex nitrate ion can change into the smaller more stable nitrite ion, or oxide ion by decomposing and releasing oxygen gas or nitrogen dioxide gas. The larger more complex carbonate ion can change into the smaller more stable oxide ion by decomposing and releasing Carbon dioxide gas. The stabilities of the nitrate and Carbonate anions are influenced by the change and size of the cations present smaller and more highly charged cations can affect these anions more.

Question 25

What is the thermal stability like of nitrates?

Answer 25

All of the nitrates of the G1 and G2 elements are white solids. When they are heated, they all decompose to nitrates or oxides. Give of nitrogen dioxide (brown fumes) and or oxygen. If the nitrate contains water of crystallisation then steam will also be observed. If no brown fumes are observed this indicates a lesser decomposition that can be represented by Metal nitrate > metal nitrite + oxygen If brown fumes are observed this indicates a greater decomposition can be represented by Metal nitrate > Metal oxide + nitrogen dioxide + Oxygen. Nitrates and Nitrites are sometimes differentiated by oxidation numbers - Nitrate (V) for nitrate, and nitrate for nitrite.

Question 26

What are the typical observations obtained by heating samples of nitrates in test tubes over a Bunsen burner flame?

Answer 26

Lithium nitrate -Brown fumes Greater decomposition Sodium nitrate - No brown fumes Lesser decomposition Potassium nitrate - No brown fumes Lesser decomposition Rubidium nitrate - No brown fumes Lesser decomposition Caesium nitrate - No brown fumes Lesser decomposition Beryllium nitrate - Brown fumes Greater decomposition Magnesium nitrate - Brown fumes Greater decomposition Calcium nitrate - Brown fumes Greater decomposition Strontium nitrate - Brown fumes Greater decomposition Barium nitrate Brown fumes Greater decomposition

Question 27

What are the trends for the decomposition of nitrates in G1 and G2?

Answer 27

Greater decomposition occurs when: The cation has a 2+ charge The cation has a 1+ charge and is the smallest Group 1 cation

Question 28

What is the thermal stability like of carbonates?

Answer 28

All of the carbonates of the G1 and G2 elements are white solids. When they are heated, they either do not decompose or decompose to oxides and give of carbon dioxides. As the gas given off is colourless and the carbonate and oxide are both white solids, there are no observations that can be made.

Question 29

What are the comparisons between different G1 and G2 carbonates when heated in a test tube over a Bunsen flame?

Answer 29

Lithium carbonate - Decomposition Sodium carbonate - No decomposition Potassium carbonate - No decomposition Rubidium carbonate - No decomposition Caesium carbonate - No decomposition Beryllium carbonate - Decomposition Magnesium carbonate - Decomposition Calcium carbonate - Decomposition Strontium carbonate - Decomposition Barium carbonate - Decomposition

Question 30

What is the trend for the thermal decomposition of Carbonates?

Answer 30

Pattern is similar to that of the nitrates. Lithium compound and all of the G2 compounds behave differently to the other G1 compounds. Lithium carbonate decomposes at lower temperatures than the other G1 Carbonates. Which don't unless at very high temperatures. All G2 carbonates decompose in the same way but with increasing difficulty down the Group. Decomposition occurs when the cation has a 2+ charge or is the smallest 1+ Group cation.

Question 31

What is the exact definition of thermal stability?

Answer 31

Thermal stability is a measure to the extent to which a compound decomposes when heated.

Question 32

What is a flame test?

Answer 32

A flame test is a simple chemical test to identify the presence of cations in a compound. However, it is important to know how to do one carefully and interpret the results. A flame test can indicate the presence of some metals in G1 and G2 of the periodic cable.

Question 33

How can a flame test be carried out?

Answer 33

A small quantity of a solid is available in a glass dish. Wear safety glasses and a lab coat. Within a fume cupboard and light a Bunsen burner. Use a dropper to add a few drops of concentrated hydrochloric acid to the solid and mix together so that the metal compound begins to dissolve. HCl can convert any metal compound to a chloride which are more volatile than other salts so give better results. Dip a clean metal wire (platinum or nichrome) into the mixture to obtain a sample of the compound. Hold the end of the wire or rod in the flame and observe the colour.

Question 34

What are the problems with the flame test?

Answer 34

Many compounds contain small amounts of sodium compounds as impurities, so the intense colour of sodium can mask other colours. Describing colours with words is subjective, people have different levels of colour vision, word description of colours may be different as well.

Question 35

What are the colour descriptions for the Group 1 cations?

Answer 35

Lithium : red Sodium : yellow/orange Potassium : lilac Rubidium : red/purple Caesium : blue/violet

Question 36

What are the colour descriptions for the Group 2 cations?

Answer 36

Beryllium : no colour Magnesium : no colour Calcium : Brick red Strontium : Crimson red Barium : Green

Question 37

What causes the colour in flame tests?

Answer 37

Electron transitions, Electrons occupy orbitals in specific energy levels in an atom these are often represented using electron configurations. Electrons can absorb energy and move to higher energy levels. The term ground state is used to describe an atom with all its electrons in their lowest possible energy levels. if an electron moves to a higher energy level, new situation described as an 'excited state'. Movement of an electron to an excited state occurs during a flame test. This movement is immediately followed by the return of the electron to its ground state, which releases energy. If this energy corresponds to radiation in the visible light spectrum then a characteristic colour appears.

Question 38

What is the test for ammonia ions?

Answer 38

Cation does not give a colour in a flame test in ammonium ion. The usual test for ammonia ions in a solid solution is to add sodium hydroxide solution and warm the mixture. The addition of sodium hydroxide causes this reaction NH4 + OH- > NH3 + H20 The warming releases ammonia gas. Ammonia can be recognised by its smell a simple chemical test is use damp red litmus paper, which turns blue (ammonia common alkaline gas) hydrogen chlorine gas reacts with ammonia to form white fumes of ammonium chloride.

Question 39

Why do Magnesium and Beryllium not have a flame colour?

Answer 39

The electron transition is magnesium corresponds to a wavelength outside the visible light spectrum so no flame colour.