How can you distinguish between primary, secondary and tertiary alcohols? With equation explain how does ethyl alcohol react with (i) acidified `K_2Cr_20_7`, solution and(ii) phosphorous pentachloride?

Explanation

Action of alcohols with heated copper is used to distinguish between primary ,secondary and tartiary alcohols .This method is also known as catalytic dehydrogenation method .
When the vapours of a primary or secondary alcohol are passed over heated copper at 573 K , dehydragenation takes place and an aldehyde or ketone is formed while teritiary alcohols undergo dehydration to form alkenes.
`R - underset (1^(@)"alcohol") (CH_(2)-OH) overset (Cu) underset (573K) to underset ("Aldehyde") (R-CHO +H_(2)) uarr`

`underset(3^(@)"alcohol")(CH_(3)-overset(CH_(3))overset(|) underset (OH) underset(|)C-CH_(3)) overset(Cu) underset(573K) to underset (2- "methylpropene") (CH_(3)-overset(CH_(3)) overset(|) C= CH_(2)+H_(2)O `
Reaction of Ethyl alcohol with acidified `K_(2)Cr_(2)O_(7)` Ethyl alcohol in presence of acidfied `K_(2)Cr_(2)O_(7)` is oxidised to an aldehyde which in turn is oxidised to a carboxylic acid
`CH_(3)CH_(2)OH overset ([O]) underset (K_(2)Cr_(2)O_(7)//H_(2)SO_(4)) to CH_(3)CHO overset ([O]) to CH_(3)COOH `