Chapter 8 - Reactivity trends Flashcards
What is the reaction of group 2 elements with water?
Group 2 elements react with water forming a metal hydroxide and hydrogen.
How does magnesium react with water?
Magnesium reacts slightly with cold water (and more vigorously with steam)
How does calcium react with water?
Calcium reacts to form a white precipitate of calcium hydroxide.
How does strontium and barium react with water?
Strontium reacts with water slowly, it reacts with water quicker than calcium, which is placed directly above strontium in the periodic chart, and slower than barium, placed directly below strontium. Strontium is water insoluble, but it does react with water.
Strontium reacts to form less precipitate (with more dissolved product) and barium reacts forming even less precipitate.
How do group 2 elements react to being heated in air, give an example with magnesium.
They burn vigorously when heated in air to form white oxides.
2Mg + O2 –> 2MgO
How do group 2 elements react with acids?
E.g. Mg and HCl
Group 2 elements react with acids to form a salt and hydrogen.
E.g. Mg + 2HCl –> MgCl2 +H2
Give two observations of magnesium when heated in oxygen.
Bright white light and white ash
What is the trend in solubility with the group 2 hydroxides and explain how this trend occurs
Going down group 2, the hydroxides become more soluble. This is because more OH- ions are released into the solution, which become more alkaline. So going down they also get more alkaline.
Suggest the uses of group 2 compounds as bases - Calcium hydroxide, Calcium carbonate and magnesium hydroxide.
Calcium hydroxide is used to neutralise acidic soils.
Calcium carbonate is used to treat acid indigestion.
Magnesium hydroxide is used to treat acid indigestion.
What observations can be made when Group 2 oxides react with water - MgO, CaO, SrO and BaO
MgO has no observable change.
CaO, SrO and BaO reactions are very exothermic. The white oxide expands as water is added, producing a lot of steam.
Explain how calcium carbonate can be used to alleviate indigestion
Indigestion is caused by excess acid in the stomach. Some antacid tablets contain calcium carbonate which neutralises the excess acid
Suggest why sodium hydroxide tablets are not used to alleviate indigestion.
Sodium hydroxide is corrosive and it would burn the body.
Write an equation for the reaction of barium oxide with water.
BaO(s) + H2O(l) –> Ba(OH)2
Explain whether the pH of calcium hydroxide would be higher or lower than barium hydroxide.
pH is lower because calcium hydroxide is less soluble so there are fewer hydroxide ions present.
How do the halogens (group 7 elements) exist?
As diatomic molecules.
Explain the trend in the halogens boiling point
The boiling point increases going down the group because as the size of the molecules increase, the London forces increase.
How is bleach made?
Bleach is made by reacting chlorine with sodium hydroxide solution to make sodium chlorate (I) solution.
Cl2 + 2NaOH –> NaCl + NaOCl
What is disproportionation and give an example
Where the same element is oxidised and reduced in the same reaction. E.g. Chlorine in the reaction to make bleach.
Cl2 + 2NaOH –> NaCl + NaOCl
Cl2 is oxidised from 0 to +1 in NaOCl
Cl2 is reduced from 0 to -1 in NaCl
Explain the advantages and disadvantages of using chlorine for water treatment.
Chlorine kills bacteria in the water because it’s toxic however it may form chlorinated hydrocarbons, which may be carcinogenic.
Write an equation of equilibrium for the reaction when chlorine is used to treat water - a chlorine molecule reacts with a water molecule to form chloric (I) acid, HClO
Cl2 + H2O ⇌ HClO +HCl
Why is Cl2 + H2O ⇌ HClO +HCl classed as a disproportionation reaction?
Chlorine’s oxidation number changes from 0 in Cl2 to +1 in HClO, which is oxidation, and to -1 in HCl, which is reduction. The oxidation and reduction of chlorine in this reaction is disproportionation.
What ions do the halogens form?
The halogens have an outer shell electronic configuration of S2P5, they form anions with a 1- charge and a full outer shell.
Explain the trend in reactivity down group 7 (the halogens)
Further down the group, less energy is released when the halide ion is formed. Reactivity reduces down the group because:
The added electron is further from the nucleus, it’s shielded by more electrons in inner shells, the electrostatic attraction of the added electron to the nucleus is reduced, less energy is released by forming the ion.
What displacement reactions occur with halogens.
A more reactive halogen will displace a less reactive halogen from its salt. Halogen solutions can be added to solutions of halide ions such as sodium chloride, sodium bromide and sodium iodide which are colourless.