hi...i need some help here :)
q1.) paracetamol (C8H9NO2) is prepared from 4-aminophenol (C6H7NO) and acetic anhydride (C4H6O3) according to the following equation
C6H7NO (4-aminophenol) + C4H6O3 (acetic anhydride) ----> C8H9NO2 (paracetamol) + C2H4O2 (acetic acid)
What is the percent yield of reaction if 100g of paracetamol is produced from 109.2g of 4-aminophenol and 102.1g of acetic anhydride?
q2.) Aspirin is produced from salicyclic acid (C7H6O3) and acetic anhydride (C4H6O3) according to the following eqn
C7H6O3 (salicyclic acid) + C4H6O3 (acetic anhydride) ----> C9H8O4 (aspirin) + C2H4O2 (acetic acid)
How many grams of aspirin would you obtain from 4.5g of salicyclic acid of the reaction is 75%?
q3.) Boron sulphide (B2S3) reacts with water to form boric acid (H3BO3) and hydrogen sulfide gas (H2S). Assume that 5.88g of B2S3 is mized with 7.85g of water.
Which reactant is limiting and which reactant is in excess?
How many grams of the excess reactant are not consumed?
How many grams of boric acid are produced?
I know the qns seem introductory but i only have lower sec chem knowledge..didnt take chem for my o levels..thks in advance!
You're right that these questions are basic stiochiometry questions that should have been mastered at 'O' level. Fair enough, you've an excuse that you didn't sit for 'O' level Chem. But you must understand that it's unfeasible (ie. there are limitations) to attempt to learn/teach stoichiometry (or chemistry calculations in general) over the internet.
I'll leave it to current secondary school and JC students on this forum to volunteer to offer you detailed worked solutions (but try not to be dissapointed if no one volunteers, coz doing the full worked solutions for stoichiometry qns can be tedious).
I'll give brief guidance, without doing the detailed worked solutions. If you don't even understand my guided steps (below), then you should urgently seek additional help (eg. from teachers, from peers who are doing well, from private tutors, etc... understand that online help via forums like this has its limitations).
Q1.
Determine moles of reactants 4-aminophenol and acetic anhydride.
Based on stoichiometry, determine limiting and excess reactants.
Based on moles of limiting reactant, calculate moles of product.
Hence calculate theoretical sample mass of product.
% yield = experimental sample mass of product / theoretical sample mass of product.
Q2.
Determine moles of salicyclic acid.
Apply stoichiometry to calculate theoretical moles of product.
Hence calculate theoretical sample mass of product.
Since % yield is given as 75%, calculate experimental sample mass of product.
Q3.
Write the balanced equation for the hydrolysis of boron sulfide to generate boric acid and hydrogen sulfide.
Determine moles of reactants boron sulfide and water.
Based on stoichiometry, determine limiting and excess reactants.
Calculate moles of excess reactant left unsed, hence calculate sample mass of excess reactant left unsed.
Apply stoichiometry (based on limiting reactant) to calculate moles of boric acid (product) generated.
Hence calculate sample mass of boric acid (product) generated.
Originally posted by yl_c:hi...i need some help here :)
q1.) paracetamol (C8H9NO2) is prepared from 4-aminophenol (C6H7NO) and acetic anhydride (C4H6O3) according to the following equation
C6H7NO (4-aminophenol) + C4H6O3 (acetic anhydride) ----> C8H9NO2 (paracetamol) + C2H4O2 (acetic acid)
What is the percent yield of reaction if 100g of paracetamol is produced from 109.2g of 4-aminophenol and 102.1g of acetic anhydride?
q2.) Aspirin is produced from salicyclic acid (C7H6O3) and acetic anhydride (C4H6O3) according to the following eqn
C7H6O3 (salicyclic acid) + C4H6O3 (acetic anhydride) ----> C9H8O4 (aspirin) + C2H4O2 (acetic acid)
How many grams of aspirin would you obtain from 4.5g of salicyclic acid of the reaction is 75%?
q3.) Boron sulphide (B2S3) reacts with water to form boric acid (H3BO3) and hydrogen sulfide gas (H2S). Assume that 5.88g of B2S3 is mized with 7.85g of water.
Which reactant is limiting and which reactant is in excess?
How many grams of the excess reactant are not consumed?
How many grams of boric acid are produced?
I know the qns seem introductory but i only have lower sec chem knowledge..didnt take chem for my o levels..thks in advance!
Q1
Molar mass of paracetamol (C8H9NO2)= (12 x 8) + (1 x 9) + 14 + (16 x 2) = 151
Molar mass of 4-aminophenol (C6H7NO) = 109
Molar mass of acetic anhydride (C4H6O3) = 102
C6H7NO (4-aminophenol) + C4H6O3 (acetic anhydride) ----> C8H9NO2 (paracetamol) + C2H4O2 (acetic acid)
Intepretation: One mol of 4-aminophenol reacts with 1 mol of acetic anhydride will produce 1 mol of paracetamol and acetic acid.
(Number of mol = Mass of sample/ Molar mass)
Calculate number of mol of reactant:
109.2g of 4-aminophenol = Mass/Mr = 1.002 mol
102.1g of acetic anhydride = Mass/Mr = 1.001 mol
So 1.001 mol of acetic anhydride will react with 1.001 mol of 4-aminophenol to produce 1.001mol of paracetamol and 1.001 mol of acetic acid.
[Read chapter on Limiting reactant] The substance that is being used up first in the reaction.
Theoritically you will be expecting 1.001 mol or 151.151 g of paracetamol. But in this case it only yield 100g.
Fractional yield = Actual yield/theoritical yield = 100g/ 151.151g = 0.662
Express in percentage = 66.2%