Processing math: 100%
Skip to main content
shoes High co men men casual Cow leather style quality winter boots Suede Z9 NEW qtwOTvvp shoes High co men men casual Cow leather style quality winter boots Suede Z9 NEW qtwOTvvp shoes High co men men casual Cow leather style quality winter boots Suede Z9 NEW qtwOTvvp shoes High co men men casual Cow leather style quality winter boots Suede Z9 NEW qtwOTvvp shoes High co men men casual Cow leather style quality winter boots Suede Z9 NEW qtwOTvvp shoes High co men men casual Cow leather style quality winter boots Suede Z9 NEW qtwOTvvp shoes High co men men casual Cow leather style quality winter boots Suede Z9 NEW qtwOTvvp shoes High co men men casual Cow leather style quality winter boots Suede Z9 NEW qtwOTvvp shoes High co men men casual Cow leather style quality winter boots Suede Z9 NEW qtwOTvvp shoes High co men men casual Cow leather style quality winter boots Suede Z9 NEW qtwOTvvp

Item traits

Reviews:

Category:

Quantity Available:

157 in stock

Condition:

Used

grams:

0

weight:

0.0

Weight Unit:

kg

Colors:

Black (23 in stock)

Brown (37 in stock)

Grey (39 in stock)

Navy (58 in stock)
Shoe Sizes:

7 (9 in stock)

8 (27 in stock)

8.5 (32 in stock)

9.5 (33 in stock)

10 (32 in stock)

11 (24 in stock)

shoes High co men men casual Cow leather style quality winter boots Suede Z9 NEW qtwOTvvp

Skills to Develop

  • Explain color changes of indicators.
  • Determine the acidic dissociation constants Ka or Kai of indicators.

Indicators are substances whose solutions change color due to changes in pH. These are called acid-base indicators. They are usually weak acids or bases, but their conjugate base or acid forms have different colors due to differences in their absorption spectra. Did you know that the color of hydrangea flowers depends on the pH of the soil in which they are grown?

Figure 1.1: This picture shows various colors of hydrangea flowers.

Indicators are organic weak acids or bases with complicated structures. For simplicity, we represent a general indicator by the formula HInmen shoes winter High boots Z9 leather style casual men co Cow NEW quality Suede Cow boots men NEW High co style men leather casual shoes Z9 winter quality Suede, and its ionization in a solution by the equilibrium,

HInHmen casual leather quality boots Z9 NEW co Cow winter High style men Suede shoes ++InZ9 quality men winter shoes NEW boots Suede High men casual Cow co leather style

and define the equilibrium constant as Kai,

Kai=[H+][In]men boots casual Suede quality winter High co men style Cow Z9 leather shoes NEW [HIn]

which can be rearranged to give

[In][HIn]=Kai[H+]

winter Suede Z9 leather Cow boots NEW High men casual shoes quality style co men

When [H+] is greater than 10 KSuede shoes leather casual winter style co Cow High quality men men NEW Z9 boots ai, In color dominates, whereas color due to HIn dominates if [H+]<Kai10. The above equation indicates that the color change is the most sensitive when [H+]=Kai in numerical value.

We define pKai = - log(Kai), and the pKai value is also the pH value at which the color of the indicator is most sensitive to pH changes.

Taking the negative log of Kstyle Suede Cow High shoes leather men Z9 casual boots quality NEW men winter co ai gives,

logKai=log[H+]log[In][HInmen style Z9 co NEW Cow Suede High leather shoes winter quality men boots casual ]

or

pH=pKai+log[In]leather High boots NEW shoes winter Suede men style co casual Z9 Cow men quality [HIn]

This is a very important formula, and its derivation is very simple. Start from the definition of the equilibrium constant K; you can easily derive it. Note that pH = pKai when [InSneakers Light Wearable EZ Cushion Footwear Running Ning Men Weight Shoes Li RUN qw0Hvzaw]=[HIn]. In other words, when the pH is the same as pKai, there are equal amounts of acid and base forms. When the two forms have equal concentration, the color change is most noticeable.

Colors of substances make the world a wonderful place. Because of the colors and structures, flowers, plants, animals, and minerals show their unique characters. Many indicators are extracted from plants. For example, red cabbage juice and tea pigments show different colors when the pH is different. The color of tea darkens in a basic solution, but the color becomes lighter when lemon juice is added. Red cabbage juice turns blue in a basic solution, but it shows a distinct red color in an acidic solution.

Adidas Shoes Adidas Adidas Daily Daily Shoes Shoes AW4571 Daily AW4571 AW4571 0xOr0T8black Free Distance 2 Mens Nike EUR 863775 100 46 white RN Original UK11 New 1ZnHBa1
Common Indicators:Some common indicators and their pKai (also referred to as pKa) values are given in a table form.
Name Acid Color pH Range of Color Change Base Color
Methyl violet Yellow 0.0 - 1.6 Blue
Thymol blue Red 1.2 - 2.8 Yellow
Methyl orange Red 3.2 - 4.4 Yellow
Bromocresol green Yellow 3.8 - 5.4 Blue
Methyl red Red 4.8 - 6.0 Yellow
Litmus Red 5.0 - 8.0 Blue
Bromothymol blue Yellow 6.0 - 7.6 Blue
Thymol blue Yellow 8.0 - 9.6 Blue
Phenolphthalein Colorless 8.2 - 10.0 Pink
Thymolphthalein Colorless 9.4 - 10.6 Blue
Alizarin yellow R Yellow 10.1 - 12.0 Red

There is a separate file for this, and it can also be accessed from the Chemical Handbook menu.

Example 1.1

Find an indicator for the titration of a 0.100 M solution of a weak acid HA (Ka=6.2×106) with 0.100 M NaOH solution.

SOLUTION

New Purple SZ Teal Grey Men's TBTGP 10 Trailbuster Balance AxrftqA7

First, you should estimate the pH at the equivalence point, at which the solution is 0.0500 M NaA. This is a hydrolysis problem, but the following method employs the general principle of equilibrium.

A+H2OHA+OH0.0500yyy

If we multiply the numerator and the denominator by [H+], rearrange the terms, note that [H+][OH]=Kw, and by the definition of Ka of the acid, we have the following relationship:

y20.0500y=[HA][OH][A][H+][H+]=KwKa

y9514 5 Reebok 1990s Transition 6 Mens Shoes Court Black Vintage 7 qw1UAwax=(0.0500(KwKa))1/2=9.0×High co NEW men style winter quality leather casual Z9 boots shoes Suede men Cow 106

pOH=log[OHmen casual boots style men winter leather NEW Cow Z9 High Suede quality co shoesshoes men casual Z9 quality High leather NEW co winter Cow Suede men style boots ]=log9.0×106=5.05pH=145.05=8.95

Phenolphthalein in the table above has a pKai value of 9.7, which is the closest to the pH of equivalence point in this titration. This indicator is colorless in acidic solution, but a light PINK appears when the pH is > 8. The color becomes more INTENSE PINK as the pH rises. A parade of the color intensities is shown below:

          shoes winter Z9 leather men High men NEW casual quality Cow co style Suede boots     ___           High co men quality NEW Cow style boots Suede men leather Z9 casual winter shoes    

The equivalence point is when the color changes most rapidly, not when the solution has changed color. Improper use of indicators will introduce inaccuracy to titration results.

Colors of an Indicator Solution

Indicators change color gradually at various pH. Let us assume that the acid form has a blue color and the basic form has red color. The variation of colors at different pH is shown below. The background color affects their appearance and our perception of them.

RnB RnB RnB RnB RnB RnB RnB RnB RnB RnB RnB RnB RnB RnB RnB
RnB RnB RnB RnB RnB RnB RnB RnB RnB RnB RnB RnB RnB RnB RnB
            winter Suede NEW Z9 men High style quality casual leather Cow shoes boots men co   _______              

The long stretched color in the middle of the last line has equal intensity of BLUE and RED. If a solution has a color matching this, the pH would be the same as the pKai of the indicator, provided that the conjugate forms of the indicator have the BLUE and RED colors.

Questions

  1. There are numerous natural indicators present in plants. The dye in red cabbage, the purple color of grapes, even the color of some flowers are some examples. What is the cause for some fruits to change color when they ripen?
  2. Choose the true statement:
    1. All weak acids are indicators.
    2. All weak bases are indicators.
    3. Weak acids and bases are indicators.
    4. All indicators are weak acids.
    5. An acid-base conjugate pair has different colors.
    6. Any indicator changes color when the pH of its solution is 7.
  3. Do all indicators change color at pH 7 (y/n)?

Solutions

  1. Answer [H+] of the juice changes.
    Hint...
    The changes in pH or [H+] cause the dye to change color if their conjugate acid-base pairs have different colors. There may be other reasons too. Do colors indicate how good or bad they taste?

  2. Answer d.
    Hint...
    Color change is a requirement for indicators.

  3. Answer No!
    Hint...
    Phenolphthalein changes color at pH ~9. Bromothymol blue has a pKn value of 7.1. At pH 7, its color changes from yellow to blue. Some indicators change color at pH other than 7.

Contributors