Question

Project 7:   Acids and Bases

A neutralization reaction depends on the transfer of a proton, hydrogen, from one substance to another. The substance that donates the proton is an acid. That which accepts the proton is a base. pH is a measure of the molar concentration of hydrogen ion in a solution. The strength of an acid is determined by its ionization potential, or the relative amount of the hydrogen ion present in a compound that can be donated. If an acid can donate most of its hydrogen and become completely, or almost completely, ionized then it is a strong acid. Strong acids have a low pH, in the 1 – 2 range. A small potential proton donation results in a weak acid and the pH will be in the 3 – 6 range. A neutral solution, one in which the molar concentrations of hydrogen and hydroxide are equal, has a pH of 7. A predominance of free hydroxide ion in a solution indicates a base. A weak base has a pH of 8 – 11 and a strong base has a pH in the range of 12 – 14.

In order to test the hydrogen ion concentration of a solution, it is often convenient to use a substance that will change color as a result of the ion being present. Such a material is called a chemical indicator. In this experiment you will use an indicator made from red cabbage. Red cabbage works because it contains a water-soluble pigment called anthocyanin that changes color when it is mixed with an acid or a base. The pigment turns red in acidic environments and bluish green in alkaline (basic) environments. The following table shows the color corresponding to approximate pH ranges.

pH range	1 - 2	3 - 5	6 - 7	8 – 9	10 – 11	12 - 13	14
Color	Red	Pink	Violet	Blue	Aqua	Green	Yellow

Procedure:

1. Tear, or cut, cabbage leaves into fairly small pieces and place them in a glass bowl.

2. Pour boiling water over the leaves to cover them completely, then let sit until the liquid is a purplish color and the solution has cooled. Remove the leaves by filtration or decantation saving the juice.

3. Pour approximately 2 Tablespoons of cabbage water into each of eight small colorless containers. Place thecontainers on plain white paper. Set one cup aside as your standard.

4. To each of the other seven containers, add a few drops of your testing solutions. Suggestions for testing solutions include, but are not limited to, lemon juice, vinegar, apple juice, baking soda, shampoo (preferably clear), conditioner (preferably clear), hand sanitizer, ammonia, laundry soap, cream of tartar and orange juice. When testing a solid material, dissolve it in water and then add a few drops of the resulting solution to a container of indicator.

Results:

1. Write the name of the solution that you tested in the appropriate box of a table.   

Strong Acid	Weak Acid	Neutral	Weak Base	Strong Base

2. If you dilute your test solution with water before adding it to the indicator does it change the pH? Why, or why not?

3. In terms of an acid base reaction, why is Alka-Seltzer used to treat stomach aches?

4. What is acid rain and how is it a problem to oceans and rivers? (A one paragraph answer is sufficient.)

5. Include a labeled picture of your experimental results.

Answer 1

Solution :

Strong Acid : Lemon juice, Apple Juice, Orange Juice.

Weak acid : Vinegar, Shampoo, cream of Tartar

Neutral PH : Hand sanitizer, Laundry Soap

Weak base : Baking Soda, Conditioner

Strong base : Amonia,

Part (b) :

If we dilute the test solution with water before adding it to the indicator, the pH value will not change because the number of Hydronium ions will remain same. and there will be no effect of pH which is simply pH = - log(H⁺)

Part (c) :

Alka - Seltzer contains three ingredients namely Asprin, sodium bicarbonate and anhydrous citric acid.

when we have acidity or stomach ache : Asprin mollify ache and reduce pain, whereas, the sodium bicarbonate and anhydrous citric acid maintains pH inside stomach using their effervescent reaction to water.

Part (c) :

Acid rain occurs when nitric acid and sulphuric acid emitted by different sources like factories, coal-burning power plants, automobiles etc, reacts with moisture present in the atmosphere and finally gets precipitated in the form of Sulphuric acid or Nitric acid. It creates serious problems for oceans and rivers and the animals dependent on them. Due to acid rain the pH level of rivers increases and as a result of this fishes and other marine animals which depend on neutral pH water find it difficult to survive in river and oceans.