More questions sent in by students:
Question:
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 + H20PS: 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!
Sean
SimpleChemConcepts
Learning Experience with A Difference
Hi Jo.
It’s always easier by starting with the definition.
Concentration of an acid refers to the amount of solute (grams or commonly Moles) dissolved in a fixed volume (1 dm3) of the solution. Concentration of an acid can be increased by adding more solute to the solution or removing some solvent. i.e. More Moles/Grams of solute in the solution.
Strength refers to how easily an acid or alkali dissociates when dissolve in water. Strength of an acid or alkali cannot be changed.
When concentration and the volume of acid given is the same, the amount (grams or Moles) of acid is then the same. Amount of gas to be produced will be dependent on the strength between the Strong & Weak Acids then.
Both sulphuric acid and hydrochloric acid are known as Strong Acid, which means they ionize completely to give H+ ions in solution. Ethanoic acid is a Weak Acid, and will only dissociates partially to give H+ ions. Since amount of H+ ions in solution determines the acidity of the acid, the stronger acid will have more H+ ions and will produce more CO2 gas when it reacts with a metal carbonates.
You are spot on for that “dona”. That is the correct concept and strategy to answer such questions on weak & strong acids. Keep it up.
i think the volume of gas will b more for the stronger acids. The weak acids will not ionise completely therefore all the ions are not available to react. some still remain as molecules
hey.
what if there are 3 acids, sulphuric acid, ethanoic acid and hydrochloric acid and they are all of the same concentration and same volume.
these 3 acids are added to equal amounts of calcium carbonate.
will the volume of carbon dioxide released be equal or more for the stronger acids?
i am rather confused about the concentration and strength of acids. i hope that someone can help me with this topic.
thank you!
should be ok one. last time my sch paper came out i wrote about ph paper.
they did not limit it just to chemical/physical test 🙂
oh my. is it ok if i say i’ll use a pH meter? =/
THANK YOU SO MUCH for the tip for the weak/strong acid question! It came out for Chem Paper 2 today and I was so relieved I saw the post just yesterday. 🙂