Basic qualitative acid/base question

  • Thread starter Spirochete
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In summary, the acidity of elements tends to increase as you move down a column in the periodic table due to the decreasing electronegativity and stability of dianions. However, this trend does not apply to elements that do not dissolve in water, and the Lewis acidity trend is more applicable to cations rather than the elements themselves.
  • #1
Spirochete
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Homework Statement



Why does acidity increase as you move down a column in the periodic table?


The Attempt at a Solution



It seems to me like the opposite should be true. For one thing, electronegativity is decreasing. And in general it seems like more protons in the nucleus should stabilize an E-H bond.
 
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  • #2
Must be a trick question...
 
  • #3
It was a serious question could you explain what you mean?
 
  • #4
Acidity is the ability to either donate a proton (Bronstead-Lowry type, doesn't apply here except for hydrogen itself) or to accept an electron pair (Lewis concept) or a substance that increases the hydronium ion concentration when dissolved in water (Arrhenius concept). The Arrhenius concept is not applicable if the element does not dissolve appreciably in water.

The Lewis acidity trend follows the electronegativity of the elements which decreases as you move down a column in the periodic table. In addition, the Lewis acidity concept deals with the acceptance of a pair of electrons. If an element were to accept two electrons, it would yield a dianion. Does the stability of dianions increase as you move down a column?
Lewis acidity usually deals with cations rather than the elements.

Were you being asked about the acidity of cations as you move down a column?

Tricksy, tricksy...
 

1. What is the difference between an acid and a base?

An acid is a substance that donates a proton (H+) in a chemical reaction, while a base is a substance that accepts a proton. Acids have a pH level below 7 and taste sour, while bases have a pH level above 7 and taste bitter.

2. How do you determine the strength of an acid or base?

The strength of an acid or base is determined by its ability to dissociate in water. Strong acids and bases completely dissociate into ions, while weak acids and bases only partially dissociate. The concentration of ions in a solution is also a measure of the strength of an acid or base.

3. What is the purpose of using indicators in acid-base reactions?

Indicators are substances that change color in the presence of an acid or base. They are used to visually determine the endpoint of a titration, which is when the acid and base have completely reacted with each other. Indicators help to accurately measure the amount of acid or base present in a solution.

4. How does temperature affect an acid-base reaction?

Temperature can affect the rate of an acid-base reaction. Generally, increasing the temperature will increase the rate of reaction, as molecules move faster and collide more frequently. However, in some cases, the rate of reaction may decrease at very high temperatures due to changes in the properties of the acid or base.

5. What is the significance of the pH scale in acid-base chemistry?

The pH scale is a measure of the acidity or basicity of a solution. It ranges from 0-14, with 7 being neutral. Acids have a pH below 7, while bases have a pH above 7. The pH scale is logarithmic, meaning that a change of one pH unit represents a tenfold change in acidity or basicity. This scale is important in understanding the properties and behavior of acids and bases in various chemical reactions.

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