metal final colour 1 green (neutral) 2 blue 3 dark blue 4 purple (strongly alkaline) The diagram shows a metal added to water with universal indicator; the ...
Question 1 Report
| metal | final colour |
|---|---|
| 1 | green (neutral) |
| 2 | blue |
| 3 | dark blue |
| 4 | purple (strongly alkaline) |
The diagram shows a metal added to water with universal indicator; the table gives the final colour. A strongly alkaline solution shows a very reactive metal forming a hydroxide. Which metal gives the most alkaline solution?
Answer Details
When a reactive metal meets water it forms a soluble hydroxide and hydrogen, which is why the universal indicator turns alkaline: \[2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2\]
The more reactive the metal, the more hydroxide is produced and the higher the pH. Reading the colours, metal 4 gives purple, the strongly alkaline end of the scale, so it produces the most hydroxide and is the most reactive.
Green means the solution stayed neutral, so that metal did not react with water at all. Blue and dark blue show weaker alkalinity, that is, slower or partial reaction. Learn the indicator sequence green (neutral), blue, dark blue, purple (strongly alkaline), and read pH as a measure of how much hydroxide has formed.
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