Choosing an Appropriate Indicator. Not every acid-base indicator is appropriate for signaling the neutralization point of a reaction. Table M Common Acid-Base.

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Presentation transcript:

Choosing an Appropriate Indicator

Not every acid-base indicator is appropriate for signaling the neutralization point of a reaction. Table M Common Acid-Base Indicators Indicator Approximate pH Range for Color Change Color Change methyl orange3.2 – 4.4red to yellow bromthymol blue6.0 – 7.6yellow to blue phenolphthalein8.2 – 10colorless to pink litmus5.5 – 8.2red to blue bromcresol green3.8 – 5.4yellow to blue thymol blue8.0 – 9.6yellow to blue Choosing an Appropriate Indicator

Recall that neutralization occurs when moles of H 1+ from the acid = moles of OH 1- from the base. Table M Common Acid-Base Indicators Indicator Approximate pH Range for Color Change Color Change methyl orange3.2 – 4.4red to yellow bromthymol blue6.0 – 7.6yellow to blue phenolphthalein8.2 – 10colorless to pink litmus5.5 – 8.2red to blue bromcresol green3.8 – 5.4yellow to blue thymol blue8.0 – 9.6yellow to blue Choosing an Appropriate Indicator

Also that the pH at neutralization may be below 7, at 7, or above 7. Table M Common Acid-Base Indicators Indicator Approximate pH Range for Color Change Color Change methyl orange3.2 – 4.4red to yellow bromthymol blue6.0 – 7.6yellow to blue phenolphthalein8.2 – 10colorless to pink litmus5.5 – 8.2red to blue bromcresol green3.8 – 5.4yellow to blue thymol blue8.0 – 9.6yellow to blue Choosing an Appropriate Indicator

The indicator chosen to signal the neutralization point must match the type of acid and base used. Table M Common Acid-Base Indicators Indicator Approximate pH Range for Color Change Color Change methyl orange3.2 – 4.4red to yellow bromthymol blue6.0 – 7.6yellow to blue phenolphthalein8.2 – 10colorless to pink litmus5.5 – 8.2red to blue bromcresol green3.8 – 5.4yellow to blue thymol blue8.0 – 9.6yellow to blue Choosing an Appropriate Indicator

If the acid is strong and the base is weak, then the indicator chosen must change color below 7. Table M Common Acid-Base Indicators Indicator Approximate pH Range for Color Change Color Change methyl orange3.2 – 4.4red to yellow bromthymol blue6.0 – 7.6yellow to blue phenolphthalein8.2 – 10colorless to pink litmus5.5 – 8.2red to blue bromcresol green3.8 – 5.4yellow to blue thymol blue8.0 – 9.6yellow to blue Choosing an Appropriate Indicator

If the acid is strong and the base is weak, then the indicator chosen must change color below 7. Table M Common Acid-Base Indicators Indicator Approximate pH Range for Color Change Color Change methyl orange3.2 – 4.4red to yellow bromthymol blue6.0 – 7.6yellow to blue phenolphthalein8.2 – 10colorless to pink litmus5.5 – 8.2red to blue bromcresol green3.8 – 5.4yellow to blue thymol blue8.0 – 9.6yellow to blue Choosing an Appropriate Indicator

If the acid is strong and the base is strong, then the indicator chosen must change color around 7. Table M Common Acid-Base Indicators Indicator Approximate pH Range for Color Change Color Change methyl orange3.2 – 4.4red to yellow bromthymol blue6.0 – 7.6yellow to blue phenolphthalein8.2 – 10colorless to pink litmus5.5 – 8.2red to blue bromcresol green3.8 – 5.4yellow to blue thymol blue8.0 – 9.6yellow to blue Choosing an Appropriate Indicator

If the acid is strong and the base is strong, then the indicator chosen must change color around 7. Table M Common Acid-Base Indicators Indicator Approximate pH Range for Color Change Color Change methyl orange3.2 – 4.4red to yellow bromthymol blue6.0 – 7.6yellow to blue phenolphthalein8.2 – 10colorless to pink litmus5.5 – 8.2red to blue bromcresol green3.8 – 5.4yellow to blue thymol blue8.0 – 9.6yellow to blue Choosing an Appropriate Indicator

If the acid is weak and the base is strong, then the indicator chosen must change color above 7. Table M Common Acid-Base Indicators Indicator Approximate pH Range for Color Change Color Change methyl orange3.2 – 4.4red to yellow bromthymol blue6.0 – 7.6yellow to blue phenolphthalein8.2 – 10colorless to pink litmus5.5 – 8.2red to blue bromcresol green3.8 – 5.4yellow to blue thymol blue8.0 – 9.6yellow to blue Choosing an Appropriate Indicator

If the acid is weak and the base is strong, then the indicator chosen must change color above 7. Table M Common Acid-Base Indicators Indicator Approximate pH Range for Color Change Color Change methyl orange3.2 – 4.4red to yellow bromthymol blue6.0 – 7.6yellow to blue phenolphthalein8.2 – 10colorless to pink litmus5.5 – 8.2red to blue bromcresol green3.8 – 5.4yellow to blue thymol blue8.0 – 9.6yellow to blue Choosing an Appropriate Indicator

1) Which of the following acid-base indicators would be appropriate to signal the end-point of a neutralization between nitric acid (HNO 3 ) and ammonium hydroxide (NH 4 OH)? (1) phenolphthalein(3) litmus (2) bromcresol green(4) thymol blue strong acidweak base

Choosing an Appropriate Indicator 2) In which of the following scenarios would a drop of thymol blue change from yellow to blue? (1) When it started in a beaker of 50 mL of 0.01M HCl and 50 mL of 0.10 M NaOH was added (2) When it started in a beaker of 50 mL of 0.01M NaOH and 50 mL of 0.10 M HCl was added (3) When it started in a beaker of 50 mL of 0.01M HF and 50 mL of 0.10 M KOH was added (4) When it started in a beaker of 50 mL of 0.01M KOH and 50 mL of 0.10 M HF was added Starts with a pH below 8. Ends with a pH above 9.6 Equal moles of H 1+ and OH 1- are being added. strong acid & strong base weak acid & strong base

Choosing an Appropriate Indicator 3)Choose an acid-base indicator that would appropriately signal the end-point of the neutralization of HBr and LiOH? ________________________________ or ________________________________ bromthymol blue litmus strong acidstrong base

Choosing an Appropriate Indicator 4)Choose an acid-base indicator that would appropriately signal the end-point of the neutralization of KOH and HC 2 H 3 O 2 ? ________________________________ or ________________________________ phenolphthalein thymol blue weak acidstrong base

Choosing an Appropriate Indicator 5)Choose an acid-base indicator that would appropriately signal the end-point of the neutralization of HNO 3 and Ca(OH) 2 ? ________________________________ or ________________________________ methyl orange bromcresol green strong acidweak base