Ka'aba

(noun)

A building at the center of Islam's most sacred mosque, Al-Masjid al-Haram, in Mecca, al-Hejaz, Saudi Arabia. It is the most sacred Muslim site in the world.

Related Terms

Examples of Ka'aba in the following topics:

  • Acid Dissociation Constant (Ka)

    • The Ka expression is as follows:
    • The logarithmic constant (pKa) is equal to -log10(Ka).
    • The larger the value of pKa, the smaller the extent of dissociation.
    • Acids with a pKa value of less than about -2 are said to be strong acids.
    • What is the pKa for acetic acid?

  • Weak Acids

    • Weak acids have very small values for Ka (and therefore higher values for pKa) compared to strong acids, which have very large Ka values (and slightly negative pKa values).
    • The Ka of weak acids varies between 1.8×10−16 and 55.5.
    • The first Ka refers to the first dissociation step:
    • This Ka value is 4.46×10−7 (pKa1 = 6.351).
    • The Ka of acetic acid is $1.8\times 10^{-5}$.

  • The Acid Dissociation Constant

    • Ka is a quantitative measure of the strength of an acid in solution.
    • The logarithmic constant, pKa, which is equal to −log10 (Ka), is sometimes incorrectly referred to as an acid dissociation constant as well.
    • Smaller Ka values yield larger pKa values.
    • An understanding of Ka is also essential for working with buffers; the design of these solutions depends on a knowledge of the pKa values of their components.
    • Another important application of Ka is with pH indicators.

  • Abscisic Acid, Ethylene, and Nontraditional Hormones

    • The plant hormone abscisic acid (ABA) was first discovered as the agent that causes the abscission or dropping of cotton bolls.
    • However, more-recent studies indicate that ABA plays only a minor role in the abscission process.
    • ABA inhibits stem elongation and induces dormancy in lateral buds.
    • ABA induces dormancy in seeds by blocking germination and promoting the synthesis of storage proteins.
    • Low soil moisture causes an increase in ABA, which causes stomata to close, reducing water loss in winter buds.

  • Strong Acids

    • More precisely, the acid must be stronger in aqueous solution than a hydronium ion (H+), so strong acids have a pKa < -1.74.
    • An example is hydrochloric acid (HCl), whose pKa is -6.3.
    • p-Toluenesulfonic acid is an example of an organic soluble strong acid, with a pKa of -2.8.

  • The Henderson-Hasselbalch Equation

    • The Henderson–Hasselbalch equation connects the measurable value of the pH of a solution with the theoretical value pKa.
    • The Henderson–Hasselbalch equation mathematically connects the measurable pH of a solution with the pKa (which is equal to -log Ka) of the acid.
    • The equation can be derived from the formula of pKa for a weak acid or buffer.
    • With a given pH and known pKa, the solution of the Henderson-Hasselbalch equation gives the logarithm of a ratio which can be solved by performing the antilogarithm of pH/pK­a:
    • What is the pH of a buffer solution consisting of 0.0350 M NH3 and 0.0500 M NH4+ (Ka for NH4+ is 5.6 x 10-10)?

  • Calculating Percent Dissociation

    • Percent dissociation represents an acid's strength and can be calculated using the Ka value and the solution's pH.
    • We have already discussed quantifying the strength of a weak acid by relating it to its acid equilibrium constant Ka; now we will do so in terms of the acid's percent dissociation.
    • Calculate the percent dissociation of a weak acid in a $0.060\;M$ solution of HA ($K_a=1.5\times 10^{-5}$).
    • Calculate percent dissociation for weak acids from their Ka values and a given concentration.

  • References

  • Culture and Religion in Pre-Islamic Arabia

    • Gods and goddesses were worshipped at local shrines, such as the Kaaba in Mecca.
    • Many of the physical descriptions of the pre-Islamic gods are traced to idols, especially near the Kaaba, which is believed to have contained up to 360 of them.
    • Idols were housed in the Kaaba, an ancient sanctuary in the city of Mecca.
    • For example, in addition to the animistic idols, the pre-Islamic Kaaba housed statues of Jesus and his holy mother, Mary.
    • The Kaaba is a cube-shaped building in Mecca held to be sacred both by Muslims and pre-Islamic polytheistic tribes.

  • Arabian Cities

    • The most important of these cities was Mecca, which was an important center of trade in the area, as well as the location of the Kaaba (or Ka'ba), one of the most revered shrines in polytheistic Arabia.
    • After the rise of Islam, the Kaaba became the most sacred place in Islam.
    • The Greek historian Diodorus Siculus, who lived between 60 BCE and 30 BCE, wrote about the isolated region of Arabia in his work Bibliotheca historica, describing a holy shrine that Muslims see as Kaaba at Mecca: "And a temple has been set up there, which is very holy and exceedingly revered by all Arabians."
    • Some time in the 5th century, the Kaaba was a place to worship the deities of Arabia's pagan tribes.