Group 1 and 2 Flashcards
What are group 2 metals also known as?
Alkali earth metals
What do group 2 metals act as?
reducing agents as they give 2 electrons
Do the metals in group 2 get more reactive going down the group?
Yes
What is the trend in ionisation energies down the group for group 1 and 2?
They decrease so becomes easier to remove the 2 outer electrons
What is the general equation of group 2 metals with oxygen?
2M +O2 = 2MO
What do Sr and Ba also form when reacted with oxygen?
Peroxides - MO2
What is the general equation for all group 2 metals with water?
M + 2H2O = M(OH)2 + H2
Which group 2 metal does not react with water?
Be
Which group 2 metal reacts extremely slowly with cold water?
Mg
What kind of solution is formed when Mg reacts with water and why?
It is weakly alkaline (pH 9) as magnesium hydroxide is only slightly soluble
What happens when Mg is heated with steam?
It reacts vigorously to make MgO and H2
Mg + H2O = MgO + H2
What happens when group 2 metals react with chlorine gas?
They form a metal chloride
What are all group 2 oxides?
Basic - except for BeO which is amphoteric (can act as both an acid and a base)
What is formed when group 2 oxides react with water?
Alkaline solutions
What is observed when MgO reacts with water?
MgO is only slightly soluble in water, so weakly alkaline solution (pH 10) formed
What is observed when CaO reacts with water?
Vigorous reaction which releases a lot of energy, causing some water to boil off as solid lump seems to expand and open (pH 11)
What is the general equation for group 2 oxides and water?
Oxide + water = hydroxide
What is calcium hydroxide known as when in solution?
Limewater
What is formed when a group 2 oxide react with sulphuric acid?
Group 2 sulphate
What happens when group 2 oxides react with sulphuric acid in terms of the actual reaction?
The insoluble sulphate forms at the surface of the oxide, so the solid oxide beneath it can’t react with acid
How can this (The insoluble sulphate forms at the surface of the oxide, so the solid oxide beneath it can’t react with acid) be prevented?
By using the oxide in powder form and stirring in which case neutralisation can’t take place
What is the general equation for group 2 oxides and HCl?
Oxide + dilute HCl = chloride + water
What is the general equation for group 2 oxides and H2SO4?
Oxide + dilute H2SO4 = sulfate + water
What do group 2 metal hydroxides form when reacted with a dilute acid?
Colourless solutions of metal salts
How do the solubility of the sulphates change going down the group?
They decrease (barium sulphate is an insoluble white precipitate)
What is the general equation for group 2 hydroxides and HCl?
Hydroxide + dilute HCl = chloride + water
What is the general equation for group 2 hydroxides and H2SO4?
Hydroxide + dilute H2SO4 = sulphate + water
Going down the group, how does the alkalinity of the solutions formed from oxides with water change?
It becomes more alkaline
What is the ionic reaction when oxides dissolve in water?
O2- + H2O = 2OH-
What happens when we have a high concentration of OH- ions?
The more alkaline the solution
What is equation for the hydroxides dissolving in water?
X(OH)2 = X + 2OH-
How does the solubility of the hydroxides change going down the group?
It increases so the concentration of OH- ions increases, increasing the pH of the solution
What is the connection between solubility and alkalinity for hydroxides?
As solubility increases, alkalinity increases
What is the solubility like for group 2 sulphates?
Decreases down the group
What is thermal decomposition?
The breakdown of a compound into 2 or more different substances using heat
What happens when group 2 carbonates break down when heated?
They form the metal oxide and CO2
What is the general equation when group 2 carbonates decompose?
XCO3 = XO + CO2
What happens when group 2 nitrates decompose when heated?
They form the metal oxide, oxygen gas and nitrogen dioxide gas
What is the general equation when group 2 nitrates decompose?
X(NO3)2 = XO +0.5O2 + 2NO2
Why does the breakdown of group 2 nitrates need to happen in a fume cupboard?
Nitrogen dioxide gas it toxic
What is needed more to breakdown the nitrates and carbonates of group 1 and 2 as you go down the groups?
Heat
How does the thermal stability of group 1 and 2 change going down the group?
It increases
Why will the smaller positive ions at the top of the groups polarise the anions more than the larger ions at the bottom of the group?
- The small positive ion attracts the delocalised electrons in the carbonate ions towards itself
- The higher the charge and the smaller the ion the higher the polarising power
What happens as a result of group 1 and 2 carbonates and nitrates being more polarised?
The more likely they are to thermally decompose as the bonds in the carbonate and nitrate ions become weaker
What will lithium carbonate produce when heated?
Lithium oxide and Carbon dioxide
Apart from lithium, do the other group 1 carbonates decompose at bunsen temperatures?
No
What is the only group 1 nitrate that will decompose completely and what does it produce?
Lithium - produces lithium oxide, nitrogen dioxide and oxygen
What is nitrogen dioxide?
A brown, toxic gas
What do the rest of the group 1 nitrates, apart from lithium, produce when decomposed?
The metal nitrite (NO2-) and oxygen
e.g.
2XNO3 = 2XNO2 + O2
Why do we need higher temperature for decomposition as you go down group 1?
It gets more difficult
What happens when metal ions are heated strongly?
They produce a colour
Why can flame tests be used to identify metal ions?
Different metal ions produce different colours when heated
What do we have to do first before we carry out a flame test?
Dip the loop of an un reactive metal (nichrome, platinum) in concentrated acid and hold it in the blue flame of a bunsen until there is no colour change
Why do we have to clean the metal loop before we carry out a flame test?
To avoid contamination
- Test will only work if there is 1 type of ion present
- 2 or more ions means colours will mix, making identification erroneous
How do we carry out the flame test?
Dip the clean loop into the solid sample and place it in the edge of the blue Bunsen flame
What should we avoid during a flame test?
Letting the wire get so hot it glows red as this can be confused with a flame colour
What does the heat of the flame test cause the electron in the metal ion to do?
Move to a higher energy level
After the electron moves to the higher energy level in a flame test, why does it not stay there?
It is unstable at this energy level so it falls back down
What creates the colour from the metal ion in a flame test?
As the electron drops back down from the higher energy level, energy is emitted in the form of visible light energy with the wavelength of the observed light
What colour does Li+ produce?
Scarlet red
What colour does Na+ produce?
Yellow
What colour does K+ produce?
Lilac
What colour does Rb+ produce?
Red
What colour does Cs+ produce?
Blue
What colour does Mg2+ produce?
No flame colour
What colour does Ca2+ produce?
Brick red
What colour does Sr2+ produce?
Red
What colour does Ba2+ produce?
Apple green
Why does Mg 2+ not have an observed flame colour?
The energy emitted is outside the visible spectrum
What is the bonding like in metal oxides? What is the exception?
Ionic - except for BeO which has covalent character
