# Figure 192 a pipette an indicator solution is added

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Chapter 3 / Exercise 46
Mathematical Practices, Mathematics for Teachers: Activities, Models, and Real-Life Examples
Larson
Expert Verified
Figure 19.2: A pipette An indicator solution is added to the sample. This will indicate the end point of the titration by a change of colour. Once the colour has changed, no more titrant is added. The volume of the titrant used is determined by subtracting the initial volume in the burette from the final volume. Titrations are repeated at least three times to ensure accurate, consistent results. If one result is inconsistent, more titrations will be required to provide a minimum of three consistent results. Consistent results are averaged together, to be used in calculations. The calculations are very similar to those you have already seen in this course. Doing accurate, precise titrations at such a small scale requires a great deal of laboratory skill. Computers and automated titrations that work with colorimetry are often used in industry now, though there is always a need for titrations and skilled laboratory technicians in some applications. The end point is the amount (the final drop) of titrant at which the colour of the indicator changes. The equivalence point occurs when the number of moles of H + ions equals the number of moles of OH ions. In order to perform an accurate titration, the endpoint and the equivalence point must be reached simultaneously. The indicator must be carefully selected, based on the identities of the acid and the base. If the wrong indicator is chosen, the titration solution will change colour at some pH other than the proper equivalence point. A strong acid/strong base neutralization produces a neutral salt. The indicator used should change colour at (or very near) pH 7. A strong acid/weak base titration produces an acidic salt. The indicator used should change colour below pH 7 at approximately pH 5 or 6. A weak acid/strong base titration produces a basic salt. The indicator used should change colour above pH 7, at around pH 8 or 9. The following table is used to help chemists select appropriate indicators when the salt produced during a titration will be acidic or basic. Other indicators exist besides the ones in Table 19.3, for higher and lower pH equivalency points. Copyright © 2010 The Ontario Educational Communications Authority. All rights reserved. ilc.org
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Chapter 3 / Exercise 46
Mathematical Practices, Mathematics for Teachers: Activities, Models, and Real-Life Examples
Larson
Expert Verified
Chemistry SCH4U-B Lesson 19 9 Table 19.3: Acid–base indicators Indicator Colour in acid Colour in base pH of colour change Methyl red Red Yellow 5.3 Litmus Red Blue 7.0 Bromothymol blue Yellow Blue 6.9 Thymol blue Yellow Blue 8.8 Phenolphthalein Colourless Deep pink 9.0 S u p p o r t Q u e s t i o n s 34. a) Explain the difference between the equivalence point and the end point. _______________________________________________________________ _______________________________________________________________