What Makes a Strong Acid or Strong Base?

Strong electrolytes are completely dissociated into ions in water. The acid or base molecule does not exist in aqueous solution, only ions. Weak electrolytes are incompletely dissociated.

Strong acids completely dissociate in water, forming H⁺ and an anion. There are six strong acids. The others are considered to be weak acids. You should commit the strong acids to memory: HCl - hydrochloric acid, HNO₃ - nitric acid, H₂SO₄ - sulfuric acid,HBr - hydrobromic acid,HI - hydroiodic acid,HClO₄ - perchloric acid- 100% dissociation isn't true as solutions become more concentrated. If the acid is 100% dissociated in solutions of 1.0 M or less, it is called strong. Sulfuric acid is considered strong only in its first dissociation step.

H₂SO₄ → H⁺ + HSO₄^-

Weak Acids

A weak acid only partially dissociates in water to give H⁺ and the anion. Examples of weak acids include hydrofluoric acid, HF, and acetic acid, CH₃COOH. Weak acids include:

· Molecules that contain an ionizable proton. A molecule wih a formula starting with H usually is an acid.

· Organic acids containing one or more carboxyl group, -COOH. The H is ionizable.

· Anions with an ionizable proton. (e.g., HSO₄^- → H⁺ + SO₄^2-)

· Cations

· transition metal cations

· heavy metal cations with high charge

· NH₄⁺ dissociates into NH₃ + H⁺

Strong Bases

Strong bases dissociate 100% into the cation and OH^- (hydroxide ion). The hydroxides of the Group I and Group II metals usually are considered to be strong bases.

· LiOH - lithium hydroxide

· NaOH - sodium hydroxide

· KOH - potassium hydroxide

· RbOH - rubidium hydroxide

· CsOH - cesium hydroxide

· *Ca(OH)₂ - calcium hydroxide

· *Sr(OH)₂ - strontium hydroxide

· *Ba(OH)₂ - barium hydroxide

These bases completely dissociate in solutions of 0.01 M or less. The other bases make solutions of 1.0 M and are 100% dissociated at that concentration. There are other strong bases than those listed, but they are not often encountered.

Weak Bases

Examples of weak bases include ammonia, NH₃, and diethylamine, (CH₃CH₂)₂NH.

· Most weak bases are anions of weak acids.

· Weak bases do not furnish OH^- ions by dissociation. Instead, they react with water to generate OH^- ions.

Control questions

1. What is meant by the term “chemical bond”?

2. Why do atoms bond with each other to form compounds?

3. What is a Chemical Bond?        

4. What are Valence Electrons?     

5. What are the electrons doing in a Metallic Bond?  

6. What is an example of Electrostatic Attraction?

7. Write an electronic formula for the following neutral atoms:

                  F, K, Be, S, P, Ca, Al, Ar.

8.  Write equations for the formation of the following compounds, using Lewis symbols: magnesium oxide from Mg and O atoms.

9. Calcium fluoride from Ca and F atoms.

10.Aluminum chloride from Al and Cl atoms.

11.Lithium oxide from Li and O atoms.

12.Aluminum oxide from Al and O atoms.

13.Write an electronic formula for the following covalent molecules, then write their structural formula using – to represent a shared pair of electrons: H₂.

14.CH₄.  15. SiCl₄. 16. F₂. 17. H₂O. 18. OCl₂. 19. PCl₃. 20. HBr. 21. CHCl_3.

       22. Write an electronic formula for the following, then write their structural formula: CS₂,

23. CO₂ 24. N₂. 25. COCl₂ (C is the central atom). 26. H₂CO (C is the central atom). 27. CaO.

28. What type of bonding do you think would be present in compounds formed by the combination of the following atoms: Hydrogen and chlorine, which form hydrogen chloride.

29. Potassium and fluorine, which form potassium and fluoride.

30. Silicon and hydrogen, which form silane, SiH₄.

PH Calculations

pH is a measure of hydrogen ion concentration; a measure of the acidity oralkalinity of a solution. Aqueous solutions at 25°C with a pH less than seven are acidic, while those with a pH greater than seven are basic or alkaline. A pH level of is 7.0 at 25°C is defined as 'neutral' because the concentration of H₃O⁺ equals the concentration of OH⁻ in pure water.

Here's a quick review of how to calculate pH and what pH means with respect to hydrogen ion concentration, acids, and bases.

pH - noun > The p ower of H ydrogen, which is a measure of the acidity or alkalinity of a solution, numerically equal to 7 for neutral solutions, increasing with increasing alkalinity and decreasing with increasing acidity.

Related Resources:

PH For Dummies

The pH (p ower of H ydrogen) level in a saltwater aquarium is a constant concern to most aquarists. Whereas the occupants in a FO (Fish Only) tank can tolerate a fairly wide range of pH levels for periods of time with no major harm, the occupants of a reef tank rely heavily on a constant pH level in the right range to just survive, let alone thrive.

Testing Your Aquarium Water

Taking the time to test your saltwater aquarium water whether it is a fish-only or reef tank system is a very important part of maintenance, as it gives you an analysis of the condition or quality of the environment your marine inhabitants are living in.

More pH & Alkalinity Resources

Information about the relationship between pH and alkalinity and how to measure and control or keep these chemical elements at steady levels.

Acids, Bases, and pH

There are several ways to define acids and bases, but pH only refers to hydrogen ion concentration and is only meaningful when applied to aqueous (water-based) solutions. When water dissociates it yields a hydrogen ion and a hydroxide.

H₂O ↔ H⁺ + OH^-

When calculating pH, remember that [] refers to molarity, M.

K_w = [H⁺][OH^-] = 1x10^-14 at 25°C
for pure water [H⁺] = [OH^-] = 1x10^-7
Acidic Solution: [H⁺] > 1x10^-7
Basic Solution: [H⁺] < 1x10^-7

Calculate pH and [H⁺]

pH = log₁₀[H⁺]
    [H⁺] = 10^{- pH}

Example:

Calculate the pH for a specific [H⁺]. Calculate pH given [H⁺] = 1.4 x 10^{-5 M}

pH = log₁₀[H⁺]
     pH = log₁₀(1.4 x 10^-5)
    pH = 4.85

Example:

Calculate [H⁺] from a known pH. Find [H⁺] if pH = 8.5

[H⁺] = 10^{- pH}
     [H⁺] = 10^{- 8.5}
     [H⁺] = 3.2 x 10^{-9 M}