The Relationship Between The Ph Value With The Molarity Of Acid

THE RELATIONSHIP BETWEEN THE pH VALUE WITH THE MOLARITY OF ACID. SCIENTIFIC CONCEPT AND THE CONCEPT OF STRONG ACID AND WEAK ACID. The pH value for acid can be determine by 2 factor. The factor are: (a) degree of dissociation (b) molarity In the same molarity, pH of given acid depend on the degree of the dissociation more highest the degree of dissociation of acid, more lower its pH and more strongest the acid

Experiment

Molarity of HCl (mol dm-

pH value

3

1 2 3 4 5

) 1.0 0.1 0.01 0.001 0.0001

0 1 2 3 4

pH can be calculated by using this formula. pH= 14-pOH pH= -log ( H+) We used this knowledge/ concept of thie equation to find the pH of the acid.

UNIQUE FEATURE OF THIS ACTIVITY.

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This data can be obtain by replace the value of mol dm-3 with H+ into the equation

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Data displayed in systematic manner, save time in drawing graph, show relationship of different molarity with pH value.

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Students will discover that a spreadsheet can be used to process data.

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Allow student to do more important thing such as analyzing the data on the graph.

TERMINOLOGY. pH: pH is a measure of the acidity or alkalinity of a solution. Aqueous solutions at 25°C with a pH less than seven are considered acidic, while those with a pH greater than seven are considered basic (alkaline). When a pH level is 7.0, it is defined as 'neutral' at 25°C because at this pH the concentration of H3O+ equals the concentration of OH− in pure water. pH is formally dependent upon the activity of hydronium ions (H 3O+),[1] but for very dilute solutions, the molarity of H3O+ may be used as a substitute with little loss of accuracy (H+ is often used as a synonym for H3O+.) Because pH is dependent on ionic activity, a property which cannot be measured easily or fully predicted theoretically, it is difficult to determine an accurate value for the pH of a solution. The pH reading of a solution is usually obtained by comparing unknown solutions to those of known pH, and there are several ways to do so. Acid: An acid (from the Latin acidus meaning sour) is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0. That approximates the modern definition of Johannes Nicolaus Brønsted and Martin Lowry, who independently defined an acid as a compound which donates a hydrogen ion (H+) to another compound (called a base). Common examples include acetic acid (in vinegar) and sulfuric acid (used in car batteries). Acid/base systems are different from redox reactions in that there is no change in oxidation state. Acids can occur in solid, liquid or gaseous form, depending on the temperature. They can exist as pure substances or in solution.

Weak acid: Only partially dissociates in aqueos solution and therefore exist in the solution as mixture of acid molecule and and their constituent ions. The conjugate conjugate base of weak acid show a slight ability to remove proton from water.(The conjugate base of a weak acid is a weak base) Strong acid: completely transfer its proton to water, leaving no undissociated molecule in the solution. Its conjugate base has a negligible tendency to be protonated ( to abstract proton) in aqueous solution. Molarity: Molarity (M/ dm-3) express the concentration of a solution as the number of moles of solute in a liter solution

ENGAGE

THE POWER OF DEGREE DISSOCAITION You are given the same solution of acid but the pH value are different from each other.Observe the pictures carefully.

Acetic acid 0.000001 M

Hydrochloric acid 1.0 M

1.What you can observe from the picture. 2. What you can say about the pH of the both acid and the relationship with the degree of dissociation? 3. What you can say about the type of acid.

EMPOWER

Steps 1, Student are given: - pH meter - beaker - measuring cylinder - hydrochloric acid 1.00 mol dm-3, 0.1 mol dm-3, 0.01mol dm-3, and 0.001 mol dm-3 2. Student needs to plan an experiment to determine the relationship between the pH value and the degree of dissociation of acid. 3. Student has to construct a hypothesis for this experiment. 4. Student need to know the effect of degree of dissociation of acid to its pH value. 5. Help student to determines the variable involved: 6. You may give the instruction to start the activity: •

50 ml of hydrochloric acid is added to dry beaker.

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A clean pH meter is immersed to 20 cm3 of acid hydrochloric as pic below:

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The pH value of different concentration of hydrochloric acid are measured one by one.

How to set up your spreadsheet:

1. Make a table with 3 column 2. Student can enter the value of dm-3 into the equation( value H+= mol dm-3) 3. After get the value, put it in a table that same line with it molarity. How to draw a graph with your spread sheet. 1. Open an Excel. 2.Highlight cell A2 to A7 and B2 to B7 3.Insert chart 4.Chart XY (scatter) 5. X axis as molarity and Y axis as pH. 6. Finish.

QUESTION From the graph and your reading: (a) Explain the relationship between the pH value and the molarity of acid

(b) Explain the shape of the graph. (c) What you can say about degree of dissociation in this graph? (d) How can the pH of a solution be determined? (e) What are the properties of acids? (e) Which solution is more acidic, one with a pH of 1or another with a pH of 3? ANSWER (a) The lowest its molarity the highest its pH (b) The shape of the graph the order of strength of acid are reverse with its molarity. (c) The highest pH of acid more highest the degree of dissociation (d) pH can be measured with a pH meter (electronically) or with indicators such as litmus. (e) The solution with a pH of 1 is more acidic than one with a pH of 3.

ENHANCE

What you can say about the pH of this substance? Answer: The ph of this substance are different from each other. More highest the degree of dissociation of acid in water more lowest its pH and more acidic the acid and vise versa. Batteries water are most acidic because it contain the sulfuric acid, while other substance has low pH value.