More questions sent in by students:
Q1) Describe an expt that you wld carry out to show that sulphuric acid is a strong acid but ethanoic acid is a weak acid
Ans: This questionis testing you on the properties of acid. There are 4 ways for you to differentiate acid – pH paper test, Reaction w Metal, Reaction with Carbonate, or Reaction with an Alkali. To differentiate the acidity of Sulphuric Acid and Ethanoic Acid, i would suggest to test the amount of CO2 Gas produced when certain amount of the acid are reacted with a certain mass of ,say calcium carbonate. Suphuric Acid, being stronger acid will tends to give off CO2 gas more and at a faster rate.
Q2)?Two salts formed?from sodium hydroxide and phosphoric acid other than NaH2PO4.
Ans: Phosphoric Acid is TRIBASIC, meaning it has 3 Hydrogen atoms to dissociate. It will form 3 salts when reacted with NaOH.
H3PO4 -> 3H+ + PO4^3-
H3PO4 -> 2H+ + HPO4^2-
H3PO4 -> 1H+ + H2PO4^-
NaOH + H3PO4 -> Na3PO4 (Ans) + H20
NaOH + H3PO4 -> Na2HPO4 (Ans) + H20
NaOH + H3PO4 -> NaH2PO4 + H20
PS: Pls note that question is not balanced yet.
Q3) Explain why NaH(2)PO(4) is both an acid and a salt.
Ans: It is an acid because it can dissociates H+ in water making the solution acidic.
It is a salt because it is made by the neutralization process of NaOH and H3PO4. Anyhow, it can also be made by the reaction of H3PO4 with Na metal or Na2CO3.
Q4)? Structural formula of repeat unit of styrene-butadiene
Ans: This should not be covered in GCE O level syllabus. Learnt this in poly/uni.
You should know the structural formulae of Styrene monomer, but the question should give you the structural formulae of butadiene. With those structures, use the theory of Addition Polymerization.
All The Best!
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