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Use the periodic table to help you answer the following question - Edexcel - GCSE Chemistry - Question 3 - 2017 - Paper 1
Question 3
Use the periodic table to help you answer the following question. Which of these metals will form coloured cations? Put a cross (✗) in the box next to your answer. ... show full transcript
Worked Solution & Example Answer:Use the periodic table to help you answer the following question - Edexcel - GCSE Chemistry - Question 3 - 2017 - Paper 1
Step 1
Which of these metals will form coloured cations?
Answer
To determine which metals form coloured cations, we refer to their electronic configurations and typical oxidation states.
- Gallium (Ga): Forms Ga³⁺, which is typically colourless.
- Chromium (Cr): Can form several coloured cations like Cr³⁺ (green) or Cr²⁺ (blue).
- Strontium (Sr): Forms Sr²⁺, which is typically colourless.
- Sodium (Na): Forms Na⁺, which is also colourless.
Thus, only chromium (Cr) should be marked with a cross (✗).
Step 2
Explain, in terms of the structure of their atoms, why caesium is more reactive than lithium.
Answer
Caesium (Cs) is more reactive than lithium (Li) primarily due to its atomic structure.
- Atomic Size: Caesium has a larger atomic radius than lithium, meaning its outermost electron is further away from the nucleus.
- Shielding Effect: In caesium, there are more inner electron shells which shield the outermost electron from the positive charge of the nucleus. This makes it easier for the outer electron to be lost during a reaction.
- Ionization Energy: Because of the larger distance and increased shielding, caesium has a lower ionization energy compared to lithium, indicating that it requires less energy to remove its outermost electron, making it more reactive.
Step 3
Step 4
Which of these is the balanced equation for this reaction?
Answer
The correct balanced equation for the reaction of chlorine with potassium bromide is:
C Cl₂ + 2KBr → 2KCl + Br₂
This indicates that one mole of chlorine reacts with two moles of potassium bromide to produce two moles of potassium chloride and one mole of bromine.
Step 5
Explain why filament light bulbs were filled with argon rather than left with air inside them.
Answer
Filament light bulbs are filled with argon gas to prevent the tungsten filament from reacting with oxygen in air.
- Reduced Oxidation: If air were inside, the high temperatures of the filament would cause it to oxidize rapidly, leading to a quicker burnout.
- Inert Environment: Argon is an inert gas, which means it does not react with the filament, prolonging its lifespan.
- Efficient Lighting: By using argon, bulbs can operate more efficiently, providing light for a longer time without degradation of materials.