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CHEMISTRY > Group 2 > Flashcards

Group 2 Flashcards

1
Q

What is ionisation energy

A

It is the amount of energy required to remove an electron from an isolated atom or molecule

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2
Q

How does Ionisation energy change down group 2?

A

-Ionisation energy decreases down group 2
-This is because as you go down the group the number of electrons shells increase
-Meaning there is an extra inner shell that shield the outer electrons from the attraction of the nucleus
-Therefore the outer electrons are further way from the nucleus, which greatly reduces the electrostatic attraction between the nucleus and outer electrons

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3
Q

Explain the change in reactivity of the group 2 elements?

A

-As you go down the group the reactivity increases
-This is because the number of shells increases
-This will mean that there is more shielding between the nucleus and outer electrons
-Therefore the attraction between the nucleus and outer shell electrons decrease, so it is easier to lose two electrons

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4
Q

What do group 2 elements react with water to form?

A

The group 2 elects react with water to produce HYDROXIDES (metal hydroxide and hydrogen)
M(s) + 2H2O(l) → M(OH)2(aq) + H2(g)
Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)

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5
Q

What do group 2 elements react with oxygen to form?

A

The group 2 elements react with oxygen to produce OXIDES (solid oxides)
2M(s) + O2(g) → 2MO(s)
2Ca(s) + O2(g) → 2Ca0(s)

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6
Q

What do group 2 elements react with chlorine to form?

A

The group 2 elements react with chlorine to produce CHLORIDES (solids white chloride)
M(s) + Cl2(g) → MCL2(s)
Ca(s) + Cl2(g → CaCl2(S)

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7
Q

How do the oxides of the group 2 react with water?

A

The oxides react readily with water to from metal hydroxides, which dissolve. The hydroxide ions make the solution strongly alkaline
However Beryllium oxide is an exception- It docent react with water and Beryllium hydroxide is insoluble. As well as Magnesium oxide is another exception- it only reacts slowly and the hydroxide isn’t very soluble

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8
Q

Show the reaction of oxides with water

A

MO(s) + H2O(l) →M(OH)2(ag)

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9
Q

Show the reaction of oxides with dilute acid

A

MO(s) + 2HCl(aq) → MCl2(aq)+ H2O(l)

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10
Q

Show the reaction of hydroxides with water

A

M(OH)2(s) + H20(l) → M(OH)2(aq)

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11
Q

Show the reaction of hydroxides with dilute acid

A

M(OH)2(s) + 2HCl(aq) → MCL2(aq) + 2H20(l)

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12
Q

State the change in solubility of the hydroxides(OH-) down the group 2 elements

A

The solubility of the hyroxide’s increase down the group 2 elements

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13
Q

State the change in solubility of the sulfates(SO42-) down the group 2 elements

A

The solubility of the sulphates decrease down the group 2 elements

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14
Q

Explain the change in thermal stability down the group 2 carbonate/nitrate ions

A

-The thermal stability increases down the group
-This is because further down group 2 the cations increase in size
-As the larger the cations will result in a lower charge density, as the charge on the ion is spread out over a larger area, and this will cause less distortion.
-And so the less distortion the more stable the carbonate/nitrate compound

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15
Q

Are group 2 compound more or less thermally stable than group 1 compounds

A

The group 2 elements are less stable
-Because the greater the charge on the cation, the greater the distortion, therefore the less stable the compound becomes
-So as group 2 cations have a +2 charge, compared to the +1 charge for Group 1 cations.
-Therefore group 2 carbonates and nitrates are less stable than those of croup 1

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16
Q

How do group 2 carbonates decompose

A

The group 2 carbonates decompose to from the metal oxide and carbon dioxide
MCO3(s) → MO(s) + CO2(g)
CaCO3(s) → CaO(s) + CO2(g)
Calcium carbonate → Calcium oxide

17
Q

How do group 2 nitrates decompose

A

Group 2 nitrates decompose to form the metal oxide, nitrogen dioxide and oxygen
2Ca(NO3)2(s) → 2CaO(s) + 4NO2 + O2(g)
Calcium nitrate → Calcium oxide + Nitrogen dioxide

Metal nitrate → Metal oxide + nitrogen dioxide + oxygen

18
Q

How do group 1 nitrates decompose

A

Group 1 nitrates decompose to form the metal nitrate and oxygen
2KNO3(s) → 2KNO2(s) + O2(g)
Potassium nitrate → potassium nitrite + oxygen

Metal nitrate → Metal nitrite + oxygen

19
Q

How can we test how easily nitrates decompose

A

-Can be tested by testing how long it take until a certain amount of oxygen is produced( enough to relight a glowing splint)
-Can be tested by testing how long it take until an amount of brown gas(NO2) is produced. This needs to be done in a fume cupboard as NO2 is toxic

20
Q

How can we test how carbonates decompose

A

-Tested by testing how long it takes until a certain amount of carbon dioxide to be produce. Tests with lime water - which is a saturated solution of calcium hydroxide. This turns cloudy with the carbon dioxide

21
Q

How to test for Carbon dioxide

A

Test by bubbling carbon dioxide through lime water. The CO2 reacts with the Lime water(which is calcium hydroxide) to form calcium carbonate which is insoluble in water and, this is the white precipitate.

22
Q

What is Milk of Magnesia

A

Milk of magnesia is a suspension of magnesium hydroxide in water, that is used as anti digestion remedy called milk of magnesia. Hydrochloric acid is needed to digest food in the stomach, however sometimes there is too much of the acid and the person develops symptoms of indigestion. Taking the milk neutralises some of the hydrochloric acid and relieves some symptoms. It has very low solubility of magnesium hydroxide, meaning that the concentration of OH- ions in medicine is all very low and does not pose a risk to health.

23
Q

Testing for sulphate ions

A

-You will need to add a solution containing barium ions, because any sulphate ions in the solution will react with the added barium ions to form a white precipitate of barium sulfate
-However Carbonate ions will also form a white precipitate with barium ions, so therefore you need add dilute nitric acid

Test:
-Add dilute nitric acid
-Add barium nitrate solution
-White precipitate forms if sulphate ions are present

Equation of the reaction is in a solution of sodium sulfate:

-Ba(NO3)2 + Na2SO4(aq) → BaSO4(s) + 2NaNO3(aq)
Ba2+(aq) + SO42-(aq) → BaSO4(s)

24
Q

Why do the group 2 nitrates not melt, instead decompose

A

The larger more complex nitrate ion can change into smaller, more stable nitrate ion or oxide ion by decomposing and releasing oxygen gas and/or nitrogen dioxide gas
The stabilities of the nitrate and carbonate anions are influenced by the charge and size of the cation present - smaller and more highly charge cations affect these anions more

25
Q

Explain what brown fumes mean if observed during decomposition of metal nitrates

A

If there are brown fumes observed, it indicates a greater decomposition. If no brown fumes observed, it indicates a lesser decomposition.
Greater decomposition occurs when
-The cation has a 2+ charge(All of the group 2 nitrates)
-The cation has a 1+ charge and is also the smallest group 1 cation(only Lithium nitrate)

26
Q

What does a flame test do

A

A flame test is a simple way to identify the presence of a cation in a compound

27
Q

How do you carry out a flame test

A

-First wear safety glasses and a lab coat
-Add a few drops of concentrated hydrochloric acid to the solid and mix together so that the compound begins to dissolve( Using hydrochloric acid is to covert any metal compound to a chloride, because chlorides are more volatile and give better results)
-Dip a clean metal wire into the mixture to obtain a sample of the compound
-Then hold the end of the wire into the flame and observe the colour

28
Q

What are the problems with a flame test

A

-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 and a word description of a colour may mean different colours to different people

29
Q

What are the flame colours of Group 1 and 2 metals and their compounds

A

Lithium - Red
Sodium - yellow
Potassium - lilac
Rubidium - red
Caesium - blue

Calcium - Brick red
Strontium - Crimson
Barium - Green

30
Q

Why do we see a flame in the flame tests

A

The energy absorbed from the flame causes electrons to move to a higher energy levels. The colour is seen as the electrons fall back down to the ‘ground state’ lower energy level, which releases energy in the form of light. If this energy corresponds to radiation on the visible light spectrum, then a colour will appear. The difference in energy between the higher and lower levels determines the wavelength of light released - which determines the colour of the light

31
Q

Why don’t we see a flame colour for magnesium

A

This is because the electron transition in magnesium corresponds to a wavelength outside the visible light spectrum, so there will be no flame colour for magnesium

32
Q

What is the test for ammonium ions

A

A cation that does not give a colour in a flame test is the ammonium ions.
-First add sodium hydroxide solution to the solid/solution
-Then warm the mixture (warming the mixture releases ammonia gas if its present)
-Then hold a damp red litmus paper over the solution, if the paper turns blue then ammonium ions are present (ammonia is the only common alkaline gas)

The addition of sodium hydroxide causes this reaction:
NH4+ + OH- → NH3 + H2O

CHEMISTRY (4 decks)

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