CSEC Chemistry Paper 2 (May 12, 2020)

Daily Revision is again from Acids, Bases & Salts (ABS)-The Basics of Bases
Having looked at acids, it is natural/automatic that we put “2” and “2” together to figure out bases. The two terms, acids and bases, go together like biceps and triceps, from Biology and debit and credit in Financial Accounting or even love and marriage, for the (scientific) conventional like myself.
If an acid is a proton donor or a substance that liberates, produces or brings forth H+ ions, then naturally those H+ ions have to go somewhere or be received by another substance. This substance on the receiving end of the proton (H+) is called a base. So, a base is a proton acceptor or if you want to get more “basic”, a substance that reacts with an acid. Just note that the reaction occurring is “the accepting of the H+.” (In fact, the pair of electrons from the base actually moves towards the H+ that is electron deficient. That’s the correct Chemistry. Chemistry is all about the movement of electron(s).)
Bases can be:
1. oxides of metals (metals combined with oxygen) e.g. MgO (OMG!!) (Find the exceptions or anomalies (Hint…amphoteric oxides)
2. hydroxides of metals (metals combined with the OH- radical e.g. NaOH and even
3. metal carbonate (metals combined with “carbonate group” e.g. CaCO3
Bases that are soluble in water are given the name alkalis. All alkalis are bases but not all bases are alkalis. (Recall subsets from Grade 8)
At the heart of every reaction of an acid and a base is neutralization. Amidst all the crazy things that we think is happening, water is being formed, as well as a salt, hence the topic, acids, bases and salts (let’s save the latter for tomorrow.)
Using number 1 above, reacting an acid and a base should yield a (salt) and water only.
Reaction is called neutralization.
e.g. HCl (aq) + MgO (s) –> MgCl2(aq) + H2O (l)
(equation not balanced… Number of entities on left hand side (LHS) and right hand (RHS) side are not the same. If you look closely, the RHS has 2Cl while one on the LHS.) Putting a “2” in front of HCl on the LHS fixes everything, so
2HCl (aq) + MgO (s) –> MgCl2(aq) + H2O (l)
Using number 2 above, reacting an acid and alkali (soluble base) yields salt and water only.
HCl (aq) + NaOH (aq) –> NaCl (aq) + H2O (l) ( All balanced)
Using number 3, an acid reacting with a carbonate is a neutralization reaction but this time, in addition to a salt and water, carbon dioxide is formed as well.
2HCl (aq) + MgCO3 (s) –> MgCl2(aq) + H2O (l) + CO2 (g) (Balanced)
I could say a bit more but Rome wasn’t built in a day. The idea is to revise & clarify, making crooked straight. Learning is like investing, a little bit on a consistent basis.
Hol’ a meds on this especially since other concepts were introduced.
Contributed by: Kemil Walford

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