Chemistry AS Chapter 8 - Reactivity Trends Flashcards
What is a reducing agent and why are all group 2 elements classed as these?
A reagent that reduces (adds electron to) another species, they themselves are oxidised. Group 2 elements are reducing agents as they will lose their two outer shell electrons and give them to another species, meaning they have reduced this species.
Group 2 element + oxygen —> ?
Metal oxide
Group 2 element + water —> ?
Alkaline hydroxide - formula is M(OH)2
Metal + acid —> ?
Salt + hydrogen
Why does reactivity increase down group 2?
The atoms of group 2 elements react by losing electrons to form 2+ ions. The ionisation energies decrease down the group because the attraction between the nucleus and the outer electrons decreases as a result of increasing atomic radius and increasing shielding, therefore making it easier to remove electrons and so increasing the reactivity
Group 2 oxide + water —> ?
OH- ions + 2+ ion of group 2 element (e.g. Ca2+)
What happens to the solubility of hydroxides in water down group 2 and why?
It increases because the hydroxide Mg(OH)2 is only slightly soluble in water as it has a low OH- concentration and a pH of 10. However, Ba(OH)2 is much more soluble in water as it has a greater OH- concentration and a pH of 13
What is the experiment to show the trend in solubility of hydroxides down group 2?
- Add a spatula of each group 2 oxide to water in a test tube
- Shake the mixture. On this scale, there is insufficient water to dissolve all of the metal hydroxide that forms. You will have a saturated solution of each metal hydroxide with some white solid undissolved at the bottom of the test tube
- Measure the pH of each solution. The alkalinity will be seen to increase down the group
What happens to the boiling point of the halogens as you go down the group and why?
- More electrons
- Stronger London forces
- More energy required to break the intermolecular forces
- Boiling point increases
What is an oxidising agent and why can we classify a halogen as one of these?
A reagent that oxidises (takes electrons from) other species, but they themselves are reduced. A halogen is an oxidising agent because it has taken one electron from a different species (oxidised it) in order to gain a full outer shell
How do we know halogen reactivity decreases down the group?
When conducting an experiment, scientists added a solution of each halogen to aqueous solutions of the other 2 halides (e.g. solution of chlorine added to two aqueous solutions containing bromine and iodine ions). If the halogen added is more reactive than the halide present it will displace it and the solution will change colour. From the results:
- Chlorine reacted with both Bromine and Iodine
- Bromine reacted with only Iodine
- Iodine has not reacted at all
Why does halogen reactivity decrease down the group?
- Atomic radius increases
- More inner shells so shielding increases
- Less nuclear attraction to capture an electron from another species
- Reactivity decreases
Define the term disproportionation
A redox reaction in which the same element is both oxidised and reduced
What is the carbonate test?
- In a test tube, add dilute nitric acid to the solid or solution to be tested
- If you see bubbles, the unknown compound could be a carbonate
- To prove the gas is carbon dioxide, bubble it through lime water and it should turn the water cloudy
What is the sulfate test?
Add a few drops of barium chloride solution to the sulfate ions in solution. If a white precipitate of barium sulfate forms then sulfate ions are present
