(a) Give chemical tests to distinguish between :(i) Propanol and propanone(ii) Benzaldehyde and acetophenone(b) Arrange the following compounds in an increasing order of their property as indicated:(i) Acetaldehyde, acetone, methyl tertbutyl ketone (reactivity towards HCN)(ii) Benzoic acid, 3,4-dinitrobenzoic acid, 4-methoxybenzoic acid (acid strength)(iii) CH3CH2CH(Br)COOH, CH3CH(Br)CH2COOH, (CH3)2CHCOOH (acid strength)

(a)(i) Propanone gives iodoform test while propanol does not give this test.
CH3COCH3 + 3I2 + 2Na2CO3 → CHI3 (Yellow ppt) + CH3COONa + 2NaI + 2CO2 + H2O
(ii) Benzaldehyde (C6H5CHO) and acetophenone (C6H5COCH3) can be distinguished by iodoform test. Acetophenone, being a methyl ketone on treatment with I2/NaOH undergoes iodoform reaction to give a yellow ppt. of iodoform. On the other hand, benzaldehyde does not give this test.
C6H5COCH3 + 3NaOI → C6H5COONa + CHI3 (Iodoform) + 2NaOH
C6H5CHO + NaOI → No yellow ppt of iodoform
(b)(i) Methyl ter-butyl ketone < Acetone < Acetaldehyde
When HCN reacts with a compound, the attacking species is a nucleophile, CN−. Therefore, as the negative charge on the compound increases, its reactivity with HCN decreases. In the given compounds, the +I effect increases as shown below. It can be observed the steric hindrance also increase in the same order.
(ii) 4-Methoxybenzoic acid < Benzoic acid < 3, 4-Dinitrobenzoic acid
Electron-donating group decrease the strengths of acids, while electron-withdrawing groups increases the strengths of acids. As methoxy group is an electron-donating group, 4-ethoxybenzoic acid is a weaker acid than benzoic acid. Nitro group is an electron-withdrawing group and will increase the strengths of acids.
(iii) (CH3)2CHCOOH < CH3CH(Br)CH2COOH < CH3CH2CH(Br)COOH
After losing a proton, carboxylic acids gain a negative charge as shown:
R−COOH → R−COO− + H+
Now, any group that will help stabilise the negative charge will increase the stability of the carboxyl ion and as a result, will increase the strength of the acid. Thus, groups having +I effect will decrease the strength of the acids and groups having -I effect will increase the strength of the acids. In the given compounds, −CH3 group has +I effect and Br− group has −I effect. Thus, acid containing Br− are stronger. The −I effect grows weaker as distance increase. Hence, CH3CH(Br)CH2COOH is weaker acid than CH3CH2CH(Br)COOH.