What is the result we get when NaOH and Na2CO3 solution are added to alcohol respectively in difference test tubes? (2)Discuss the reactions of aldehydes with fehling's solution.Give the relevant equation. (3)How would ethanoic acid react with ammonia(NH3) and sodium hydroxide(NaOH) respectively? (4)Why would you regard an amine as a base? (5)What do you notice when you a little quantity of th sample wit diluted NaOH?
(1) When NaOH and Na2CO3 solutions are added to alcohol in separate test tubes, the following reactions occur:
- NaOH (sodium hydroxide) is a strong base. When it reacts with alcohol, it undergoes a neutralization reaction to form water and a salt called an alkoxide. The general equation for this reaction is:
NaOH + ROH → H2O + RONa
Where ROH represents the alcohol and RONa represents the alkoxide salt.
- Na2CO3 (sodium carbonate) is a weak base. When it reacts with alcohol, it can undergo a weak acid-base reaction, forming water and releasing carbon dioxide gas. The general equation for this reaction is:
Na2CO3 + 2 ROH → 2 H2O + CO2 + 2 RONa
Where ROH represents the alcohol and RONa represents the alkoxide salt.
(2) When aldehydes react with Fehling's solution, which is a blue solution containing copper ions, they undergo a redox reaction. Fehling's solution is a combination of copper(II) sulfate, sodium tartrate, and sodium hydroxide. The reaction typically involves the reduction of copper(II) ions to copper(I) oxide. The overall equation for the reaction is:
RCHO (aldehyde) + 2Cu2+ + 5OH- → RCOOH (carboxylic acid) + Cu2O + 3H2O
Where RCHO represents the aldehyde, RCOOH represents the carboxylic acid, Cu2O represents copper(I) oxide, and H2O represents water.
(3) When ethanoic acid (CH3COOH) reacts with ammonia (NH3) and sodium hydroxide (NaOH), the following reactions occur:
- With ammonia: Ethanoic acid reacts with ammonia gas to form an ammonium salt. The reaction is an acid-base reaction, and the product formed is ammonium ethanoate:
CH3COOH + NH3 → CH3COONH4
- With sodium hydroxide: Ethanoic acid reacts with sodium hydroxide to form sodium acetate and water. The reaction is also an acid-base reaction, resulting in the formation of a salt and water:
CH3COOH + NaOH → CH3COONa + H2O
(4) Amines can be regarded as bases because they can accept a proton (H+) to form a positively charged ammonium ion. Amines have lone pairs of electrons on the nitrogen atom, which can readily accept a proton from an acid. This proton transfer reaction leads to the formation of a new bond and the generation of a conjugate acid. The basicity of an amine is determined by the availability of its lone pair of electrons to accept a proton.
(5) When a little quantity of the sample is mixed with diluted NaOH, the observation can depend on the nature of the sample. However, a common observation is the formation of a precipitate or the generation of a gas.
- If the sample contains a metal cation that forms an insoluble hydroxide, such as calcium (Ca2+), magnesium (Mg2+), or iron (Fe3+), a white precipitate may form.
- If the sample contains a weak acid, it may not show any immediate visible changes when mixed with NaOH. However, the pH of the solution may increase due to the neutralization reaction between the weak acid and NaOH.
- If the sample contains an organic compound that can react with NaOH, such as a carboxylic acid, an ester, or an amine, a chemical reaction may occur, resulting in the formation of a new compound or the release of gas. The specific observation would depend on the specific reaction taking place.