GCSE Chemistry Revision Acids and Alkalis

hi and welcome back to freesciencelessons.co.uk by the end of this video you should be able to describe what's meant by an acid base and an alkali you should then be able to describe how the ph scale gives information on acids and alkalis and finally you should be able to describe the neutralization reaction between acids and alkalis now we use acids lot in science very common acid is hydrochloric acid which i'm showing you here the formula of hydrochloric acid is hcl now usually when we write the formula of an acid we also include the letters aq in brackets like this aq means aqueous solution in other words dissolved in water two other acids that we use lot are sulfuric acid and nitric acid and i'm showing you these here okay now there's one key factor about acids which you need to learn in aqueous solutions acids produce hydrogen ions in other words plus this shows hydrochloric acid in aqueous solution as you can see the molecule has split and released plus we've also made the chloride ion cl minus molecules of sulfuric acid also split in aqueous solution again we're producing the hydrogen ion plus in this case we're also producing the sulfate ion so42 minus this shows nitric acid in aqueous solution again you can see we're producing the hydrogen ion plus but this time we're also producing the nitrate ion no3 minus coming up we're going to look at bases and alkalize and what's meant by the ph scale okay now another category of chemicals that we often use in chemistry are bases and alkalis so we're going to look at those now should point out that this can look bit complicated but stick with it and it will become clearer bases are chemicals which can neutralize acids producing salt and water we're going to be looking at that in more detail in later videos bases are usually metal oxides or metal hydroxides and i'm showing you some bases here we've got copper oxide iron 3 hydroxide and sodium hydroxide all of these are bases because they can neutralize acids producing salt and water now bases which are soluble in water are called alkalis copper oxide and iron iii hydroxide are both insoluble in water so these are bases only however sodium hydroxide is soluble in water so sodium hydroxide is both base and an alkali so to recap bases are chemicals which can neutralize acids producing salt and water bases which are soluble in water are also called alkalis here's key factor about alkalis that you need to learn in aqueous solution alkalis produce hydroxide ions in other words minus i'm showing you that here for sodium hydroxide as you can see the sodium hydroxide is splitting and it's producing the sodium ion na plus and the hydroxide ion minus so remember that aqueous solutions of alkalis contain the hydroxide ion minus now the ph scale tells us the acidity or alkalinity of solution and you need to learn these values acids have ph between 0 and 6. solutions with ph of 7 are neutral and alkaline solutions have ph between 8 and 14. now we can determine the ph of solution using either ph probe or universal indicator ph probe determines the ph electronically whereas universal indicator changes color depending on whether solution is acid alkali or neutral green shows neutral solution in other words ph 7. very acidic solutions produce red color whereas purple color shows very alkaline solution we're going to finish by looking at the neutralization reaction between an acid and an alkali remember that acids produce the hydrogen ion plus and alkalis produce the hydroxide ion minus when we react an acid with an alkali the hydrogen ions react with the hydroxide ions to produce water like this this is the equation for neutralization and you do need to learn this remember you'll find plenty of questions on acids bases and alkalis in myovision workbook and you can get that by clicking on the link above