Acids alkalis and titrations

• Methyl orange changes colour from yellow to red in alkaline solutions and from red to yellow in acidic solutions.
• Phenolphthalein changes colour from pink to colourless in alkaline solutions and from colourless to pink in acidic solutions.
• Litmus, phenolphthalein and methyl orange are used to distinguish between acidic and alkaline solutions.
• Litmus solution is blue in alkaline solutions and red in acidic solutions.
• Litmus paper changes colour from blue to red in acidic solutions and stays blue in alkaline solutions.
• The pH scale measures the acidity or alkalinity of a solution, and can be measured using universal indicator or a pH probe.
• The pH scale, which ranges from 0 to 14, is used to classify solutions as strongly acidic (0-3), weakly acidic (4-6), neutral (7), weakly alkaline (8-10) and strongly alkaline (11-14).
• pH 7 is neutral, and values below pH 7 are acidic, while values above pH 7 are alkaline.
• Universal indicator can be used to measure the approximate pH value of an aqueous solution by adding a couple of drops of solution to a piece of universal indicator paper and observing what colour it changes to.
• Repeat the experiment until you get concordant results.
• Alkalis produce OH- ions in aqueous solutions.
• Acids in aqueous solution are a source of hydrogen ions and alkalis in an aqueous solution are a source of hydroxide ions.
• The titre, or the volume of acid needed to exactly neutralise the acid, is the difference between the first (100cm3) and second readings on the burette.
• The ionic equation for any alkali-acid neutralisation reaction is: H+ (aq) + OH- (aq) -> H2O(l).
• To carry out an acid-alkali titration, first wash the burette using acid and then water.
• Alkalis can neutralise acids.
• Add a few drops of a suitable indicator, such as phenolphthalein, to the conical flask; phenolphthalein is pink when alkaline and colourless when acidic.
• A neutralisation reaction is one between an acid and a base.
• Add acid from the burette to the alkali until the end-point is reached, as indicated by the indicator.
• Fill the burette to 100cm3 with acid, positioning the base of the meniscus on the 100cm3 line.
• Use a 25cm3 pipette to add 25cm3 of alkali into a conical flask, drawing the alkali into the pipette using a pipette filler.
• Acids produce H+ ions in aqueous solutions.