1. Definition of Acid and Bases:
1.1 Arrhenius definition of acid and base:
Arrhenius Acid:
The substance or a compound which gives H+ ions in aqueous solution Arrhenius base: Base is a substance or compound that produces OH- ions in aqueous solutions. Chemists have known for some time that the H+ ion doesn’t exist in aqueous solutions as an independent species. The modernized Arrhenius definition of acid is that they are substances that produce H3O+ ions in aqueous solutions. It did not take longer for chemist to find other problems with the Arrhenius definition. In practical terms, the OH- ion is far from being the only base.
1.2 Bronsted-Lowry definition:
Bronsted-Lowery definitions acid and a base,
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Example: HN03 dissociates completely in water to form H+ and N031-.
The reaction is HNO3 → H+ + N031-
A 0.01 M solution of nitric acid contains 0.01 M of H+ and 0.01 M N03- ions and almost no HN03 molecules. The pH of the solution would be 2.0. Following 6 are strong acids
1. HCl
2. H2SO4
3. HNO3
4. HClO4
5. HBr
6. HI
2. Weak acids:
A weak acid only partially dissociates in water to give H+ and the anion is called weak acid.
Example: HF dissociates in water to give H+ and F-. It is a weak acid.
HF ↔ H+ + F-
1) Strong Bases:
They dissociate 100% into the cation and OH- (hydroxide ion).
Example:
NaOH → Na+ + OH-
2. Weak Bases:
Weak bases do not furnish OH- ions by dissociation. They react with water to furnish the OH- ions. For example, When a weak base reacts with water the OH- comes from the water and the remaining H+ attaches itself to the weak base, giving a weak acid as one of the products. You may think of it as a two-step reaction similar to the hydrolysis of water by cations to give acid solutions.
NH3 + H2O → NH4+ + OH-
Reactions of Acids:
A) Reaction of acid with metals: Acid react with metals such as
Metal + acid ==> a salt + hydrogen Example:
Grey-silvery solid zinc dissolves with effervescence to evolve hydrogen gas and leave a colourless solution of the salt zinc chloride.
Zn + 2HCl ==> ZnCl2 + H2
Zn + 2HCl ==>ZnCl2 + H2
. A strip of magnesium ribbon
Neutralization reactions are those that involve the reaction of an acid and a base to form water and salt. A solution with a high hydrogen ion concentration is acidic, and a solution with a high concentration of hydroxide ions is
3) Hydrolysis - Water used to breakdown molecules. Hydro means water and lysis means to breakdown. An example of hydrolysis in action within our bodies is how our body breaks down protein into amino acids. Water is used to break protein down in to its amino acids.
will have a pH between 1 and 6 and the weak bases between 8 and 14. The exact order of weak acids and weak bases is determined by comparing the ionization constants (Ka for the weak acids and Kb for the
To start out this study the difference between acids and bases has to be identified. Acids have very low pHs and have a high concentration of hydronium ions, while bases have a high pH and have a high concentration of hydroxide ions. The difference between strong bases and acids, and weak bases and acids is the amount of dissociation. Strong bases and acids dissociate a large amount and let go of their ions in solution, while weak bases and acids may only let go of some of their ions. This is important because if the unknown solutions aren’t strong acids or bases then using their ions to calculate the pH of the solutions will give false results (Diffen 2012).
Acids differ considerable as to their strength. The difference between weak and strong acids can be as much as 10 orders of magnitude. Strong acids dissociate more completely than weak acids, meaning they produce higher concentrations of the conjugate base anion (A-) and the hydronium cation (H30+) in solution.
pH is also known as a measure of hydrogen ions in a solution. A hydrogen ion is the nucleus of a hydrogen atom being split from its electron. Studying the pH of different types of soil being placed in a control group such as tap water will represent the acidity or alkalinity of the matter. The pH scale begins at 0 and goes all the way up to 14, pH 7 being its neutral point, which isn’t acidic or basic. A neutral point on the acidic scale is in the middle, anything lower than the neutral point (7), is acidic, and anything higher than the neutral point is considered basic or “alkaline”.
4. NaOH, sodium hydroxide is a strong base. It reacts with HCl and forms NaCl and H2O.
Aqueous solutions of ionic substances will be experimented with in this Ionic Reactions lab. Aqueous solutions are solutions that water is solvent. After ionic substances dissolve in water, ions separate and become surrounded by water molecules. When these ion separate, its called dissociation.
When using different methods to measure pH levels there are some tools that can be useful. Some more than others but by putting into action the different methods it may determine which tools will work best and give the best results when testing the pH within a solution. The pH, which stands for the proportion of hydrogen ions in a solution, could be acidic (acidosis), neutral or basic (alkaline). The pH scale goes from numbers 1 through 14. A pH of 7 is neutral;
a. Aqueous Sodium Hydroxide—NaOH (aq) is a very strong base, which will completely disassociate into Na+ and OH- ions, which would make it a very strong electrolyte. Chemical reaction of the disassociation of Sodium Hydroxide: NaOH (aq)Na+ (aq)+ OH-(aq)
Ka is the acid dissociation constant and [HA] is the concentration of the weak acid . Strong acids usually completely dissociate and has a Ka value greater than 1. Weak acids don’t dissociate completely and have a Ka value much smaller than 1. pKa values are often used for weak acids due to being able to work with whole numbers
Sodium metal is extremely reactive in comparison to hydrogen due to its ranking in the activity series, and when combined with water, it would displace one of the hydrogens in a water molecule, forming NaOH, also known as sodium hydroxide (Beran, 2014). This compound is known to be basic because it can donate a hydroxide ion, and all basic substances turn litmus paper blue (Beran, 2014).
The pH of a solution is the measure of the concentration of charged Hydrogen ions in that given solution. A solution with a pH lower than seven is considered to be acidic. A solution with a higher pH is a base. It is very important for organisms to maintain a stable pH. Biological molecules such as proteins function only at a certain pH level and any changes in pH can result in them not functioning properly. To maintain these constant pH levels, buffer solutions are used. A buffer solution can resist change to small additions of acids or base’s. A good buffer will have components that act like a base, and components that act like an acid.
In 1909 S.P.L. Sorensen published a paper in Biochem Z in which he discussed the effect of H1+ ions on the activity of enzymes. In the paper he invented the term pH to describe this effect and defined it as the -log[H1+ ]. In 1924 Sorensen realized that the pH of a solution is a function of the "activity" of the H1+ ion not the concentration and published a second paper on the subject. A better definition would be pH=-log[aH1+ ], where aH1+ denotes the activity of the H1+ ion. The activity of an ion is a function of many variables of which concentration is one. It is unfortunate that chemistry texts use a definition for pH that has been obsolete for over 50 years.
The hydrogen ion (H+) concentration is extremely important to living organisms. Even small changes in H+ ¬¬ion concentration can cause serious consequences to the structural and functional integrity of molecules. Consequently, it is important to regulate the pH within strict limits so that important biochemical processes of living systems can proceed normally.