In Experiment 1, salicylic acid was treated with an excess of acetic anhydride to synthesize aspirin. Once the reaction went to completion, water was added to the flask and the solution was heated. What was the primary reason for adding water

See explanation

Explanation:

Aspirin is a very important pain killer. The production of aspirin involves a reaction between salicylic acid and excess acetic anhydride.

Usually, a small amount of a mineral acid is added as a catalyst.

Aspirin is actually acetyl salicylic acid. When this substance is formed, the substance is not really soluble in water. Addition of water leads to the precipitation of the aspirin product.

Hence, the addition of water is mostly to precipitate the pure aspirin product after reaction.

Given:

Mass of methanol = 1.02 g

To determine:

Enthalpy for the reaction of 1.02 g of methanol with excess O2

Explanation:

Balanced equation-

2CH3OH(g) + 3O2(g) → 2CO2(g) + 4H2O(g)

The reaction enthalpy is given as:

ΔHrxn = ∑nH°f(products) - ∑nH°f(reactants)

where n = number of moles

H°f = standard enthalpy of formation.

ΔHrxn = [2H°f(CO2(g)) + 4H°f(H2O(g))] - [2H°f(CH3OH(g)) + 3H°f(O2(g))]

           = [2(-393.5) + 4(-241.8)]-[2(-201.5) + 3(0)] = -1351.2 kJ

Now, 1 mole of CH3OH = 32 g

The calculated ΔHrxn corresponds to 2 moles of CH3OH. i.e.

The enthalpy change for 64 g of Ch3OH = -1351.2 kJ

Therefore, for 1.02g gaseous methanol we have:

ΔH = 1.02 * -1351.2/64 = -21.5 kJ

Ans: The enthalpy for the given reaction is -21.5 kJ