Category: Interesting Questions

A common question is where you need to determine Kc for a reaction given Kc for some other, related, reaction. These often look tricky but are very quick to do if you know how to do them. Have a look at the three reactions and Kc below: Can you see the relationship between reaction (1)…

A much harder class of Kc problem is where you are given Kc and the initial amounts. From this, you must determine the equilibrium amounts of all the substances. Here, we will need to use and ICE table and “x” for our unknown. The example below is unlikely to appear on an A Level paper,…

There are several possible variants of a Kc question. The most straightforward is where you are given equilibrium concentrations and you just need to plug them into the correct Kc expression to get the answer and unit. Alternatively, you might be given Kc and all but one of the equilibrium concentrations. With a bit of…

Weak acids (HA) react with strong bases (OH–) to form a salt and water.  One of two things can happen: HA is in excess. The product mixture is acidic due to HA and H+ remaining. OH– is in excess. The product mixture is alkaline due to OH– remaining. An early step in any calculation will therefore…

Another method of making a buffer is to react a limiting amount of strong base (e.g., NaOH) with an excess of weak acid (e.g., CH3COOH). This results in partial neutralisation of the weak acid, and a solution with a large reservoir of both HA and A-. The word react is emphasised above because this is…

One method of making a buffer solution is to mix a weak acid (e.g., CH3COOH) with a soluble salt of its conjugate base (e.g., CH3COONa). This results in partial neutralisation of the weak acid, and a solution with a large reservoir of both HA and A-. The word mix is emphasised above because this is…

A buffer solution has a large reservoir of weak acid HA and its conjugate base A–. Buffer solutions resist changes in pH when a small amount of H+ is added because most of the added H+ reacts away with A– forming HA. A– + H+ –> HA Similarly, buffer solutions resist changes in pH when…

A weak acid (HA) is an acid that dissociates partially into H+ and A–. We measure the extent of dissociation with the acidity constant KA. The greater the extent of dissociation, the “stronger” the weak acid is, and the greater KA is. The dissociation of a weak acid produces H+ and A– in equal amounts,…

Strong acids (H+) react with strong bases (OH–) to form a salt and water.  One of two things can happen: H+ is in excess. The product mixture is acidic due to H+ remaining. OH– is in excess. The product mixture is alkaline due to OH– remaining. An early step in any calculation will therefore be…

Dilution of a strong acid with distilled water increases pH. Dilution of a strong base with distilled water decreases pH. The two statements above might seem a bit confusing and contradictory at first but if we work through the numbers, its true! If you’re happy with maths, one of the quickest ways to solve a…