Hydrangea color

The color change of hydrangeas is exactly the opposite of that for litmus. 

You may be surprised to learn that many metal cations act as weak acids in water solution. A 0.10 M solution of A12(S04)3 has a pH close to 3 you can change the color of hydrangeas from red to blue by adding aluminum salts to soil At first glance it is not at all obvious how a cation such as Al3+ can make a water solution addic. However, the aluminum cation in water solution is really a hydrated species, A1(H20)63+, in which six water molecules are bonded to the central Al3+ ion. This spedes can transfer a proton to a solvent water molecule to form an H30+ ion ... 

There are many naturally occurring indicators. For instance, a single compound is responsible for the colors of red poppies and blue cornflowers the pH of the sap is different in the two plants. The color of hydrangeas also depends on the acidity of their sap and can be controlled by modifying the acidity of the soil (Fig. 11.11). 

FIGURE 11.11 The color of these hydrangeas depends on the acidity of the soil in which they are growing acid soil results in blue flowers, alkaline soil results in pink flowers. 

Hiroshima, 721 histidine, 443, 774 hole, 195 homeostasis, 386 HOMO, 126, 580 homogeneous alloy, 202 homogeneous catalyst, 565 homogeneous equilibria, 362 homogeneous mixture, F53 homolytic dissociation, 80 homonuclear diatomic molecule, 103 Hooke s law, 92 hormone, 670 horsepower, A4, 791 hour, A4 HPLC, 354 HRF products, 723 HTSC, 192 Humphreys series, 51 Hund, F 35 Hund s rule, 35, 37 Hurricane Rita, 144 hyaluronic acid, 344 hybrid orbital, 109 hybridization bond angle, 131 molecular shape, 111 hydrangea color, 463 hydrate, F32 hydrate isomer, 676 hydration, 178 hydrazine, 627... 

The colors of flowering plants such as hydrangeas are highly sensitive to soil acidity. At pH > 6.5, these showy flowers are deep pink, but at pH < 5, the blossoms are vivid blue. The chemistry of these changes involves complexation of aluminum by pigments that have acidic groups, as the structures show. 

If gardeners want blue flowers, they often add aluminum sulfate [AI2(S04)3] or sulfur to the soil to reduce the pH to 5.5. For people who prefer pink, lime (a base) is used to bring the pH to 6.5 or above. Occasionally, a hydrangea bush will produce purple flowers. This color is difficult to obtain, however. Purple flowers only come about when the pH is between... 

Why do hydrangeas vary in color when grown in dry versus wet regions See p. 122. 

Why Do Hydrangeas Vary in Color When Grown in Dry versus Wet Regions ... 

Hydrangeas are popular summer flowers as a consequence of their vivid color that persists throughout the season. Large blooms of pink and blue colors are common, but the predominant color varies with a number of environmental factors. What role does chemistry play in determining the hue of these magnificent flowers ... 

Certain varieties of hydrangeas are extremely popular for their ability to vary in color from blue to pink with growing conditions (see color Fig. 9.4.1). Research has determined that the actual mechanism for color variation is determined by the concentration of aluminum compounds in the flowersJ J In the presence of aluminum, blue flowers result in the absence of aluminum compounds, pink flowers predominate. 

Many gardening books will state that the acidity of the soil affects the color of certain varieties of hydrangeas. The soil pH affects the availability of aluminum in the soil and thereby indirectly affects the flower color. A low pH or acidic conditions will yield blue blooms pink blossoms will be favored by a higher pH or alkaline conditions. A purple color is the result of a more moderate pH level. Potting soils with a high level of peat moss will produce blue hydrangeas. Areas... 

The plant pigments responsible for the variable coloration in hydrangeas is the class of pigments known as the red and blue anthocyanins. The anthocyanins are water soluble and display a color dependent on the acidity of their environment in the flower petal vacuoles. In acidic solution, the general structure of an anthocyanin is given by Fig. 9.4.2, with a formal charge on one oxygen atom and... 

Figure 9.4.1 The blue and pink colors of hydrangeas that result from growing in soil with different degrees of acidity. From Masterton and Hurley, Chemistry Principles and Reactions, 4th edition. Orlando Harcourt, 2001. Photo courtesy of Charles D. Winters. 

Kondo, T. et al.. Cause of flower color variation of hydrangea, Hydrangea macrophylla, Tennen Yuki Kagobutsu Toronkai Koen Yoshishu, 41, 265, 1999. 

Asen, S., Stuart, N.W., and Siegelman, H.W. 1959. Effect of various concentrations of nitrogen, phosphorus and potassium on sepal color of Hydrangea macrophylla. Am. Soc. Hort. Sci. 73 495-502. 

People can use pH indicators to help maintain the correct acid-base balance in a swimming pool, to create soil conditions that are ideal for plant growth, or to make a medical diagnosis. Indicators change colors at different pHs. Some plants are natural pH indicators. Hydrangeas, for example, produce blue flowers in acidic soil, but in basic soils their flowers are pink. 

The systematic investigation of natural colors led to the discovery of several dyes and dye classes which are able to change their color. Thus, it was found that the origin of the color of hydrangea blossoms is an anthocyan dye. 

The color of the blooms on the hydrangea plant, which can be pink, blue, or purple, are determined by the amount of acidity in the soil. 

The color of the big-leaf hydrangea can vary from pink to blue depending upon the acidity of the soil in which it is grown. 

The color of the petals of the hydrangea is formed by molecules that behave as acid-base indicators. The color is influenced by the pH of the soil in which the hydrangea is grown. 

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