Question

how will you determine the pH of dilute NaOH? what will you observe

Answer 1

● First calculate the value of concentration of OH- ions.
● Find pOH from the value.
● Subtract the value of pOH from 14.
● You'll get the value of pH

Answer 2

The acidic, basic or neutral character of any solution can be expressed by expressing its H+ ion concentration. A Danish biochemist Peter Sorensen suggested a method of expressing the concentration of H+ ions in terms of pH. In Danish language, pH stands for protenz de hydrogen which means power of H+ ions. pH of a solution is given by
pH = -log [H+] = log 1[H+]
where [H+] = concentration of hydrogen ions in solution.
To report the pH, a scale from 0 to 14 was devised.
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For an acidic solution, pH is less than seven.
For a basic/alkaline solution, pH is greater than seven.
For a neutral solution, pH is equal to seven.
The pH of a solution is measured accurately using an apparatus known as pH meter. An approximate value of pH can be obtained by using universal indicator/pH paper.
Indicators: are the substances which change the colour at a certain pH. Some common examples of indicators are litmus, phenolphthalein and methyl orange. Out of these, litmus is a natural indicator while phenolphthalein and methyl orange are synthetic indicators. The colour of these indicators in different medium is given in the following table:cbse-class-10-science-practical-skills-ph-of-samples-2Universal indicator is a homogeneous mixture which is prepared by mixing a number of common indicators together. It can undergo series of colour change over a pH value ranging from 1-14 to indicate acidity or alkalinity of solutions.
Colour changes observed using universal indicator are given in the following table:
TABLE: Colour of Universal Indicators at Different pH Valuescbse-class-10-science-practical-skills-ph-of-samples-3
pH paper is a strip of paper which is coated with universal indicator. It is used to measure the acidity or alkalinity of aqueous solutions. To know the pH value of a solution, a drop of solution is placed on the pH strip. The colour produced tells the pH value of the test solution.cbse-class-10-science-practical-skills-ph-of-samples-4

NATURE OF CHEMICALS USED IN THIS EXPERIMENT
Hydrochloric acid: The chemical formula of hydrochloric acid is HCl. This is a strong acid which is formed by dissolving hydrogen chloride gas in water. In aqueous solution, it gets ionized completely and forms hydrogen ions and chloride ions. The pH of hydrochloric acid is less than 7.
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Sodium hydroxide: The chemical formula of sodium hydroxide is NaOH. In laboratory, it is found in the form of pellets or flakes. Sodium hydroxide is a strong base. On dissolving in water, sodium hydroxide gets ionized completely into sodium ion and hydroxide ion. The pH of sodium hydroxide solution is more than 7.
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Ethanoic acid: Ethanoic acid is also known as acetic acid. Its chemical formula is CH3 It is a weak acid. In aqueous solution, it gets ionized partially to give hydrogen ion and acetate ion. The pH of ethanoic acid solution is less than 7.
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Lemon juice: Lemon juice is a mixture of acids, carbohydrates and minerals. Due to presence of acids, it is acidic in nature and has pH less than 7.
Water: The chemical formula of water is H2 It is neutral in nature and thus, its pH value is 7.
Sodium bicarbonate: It is also known as baking soda or sodium hydrogen carbonate. Its- chemical formula is NaHCO3. It is a weak base. On dissolving in water, it gets ionized partially to give sodium ion and bicarbonate ion. The pH of solution of sodium bicarbonate is greater than 7.
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AIM
To find the pH of the following samples by using pH paper/universal indicator:

Dilute hydrochloric acid (HCl)
Dilute sodium hydroxide (NaOH) solution
Dilute ethanoic acid (CH3COOH) solution
Lemon juice
Water
Dilute sodium bicarbonate (NaHCO3) solution.
MATERIALS REQUIRED
Test tubes, test tube stand, droppers or glass rod, pH paper/universal indicator, standard colour chart, glazed white tile and samples of dil. HCl, dil. NaOH, dil. ethanoic acid (acetic acid/vinegar), lemon juice, distilled water and dil. sodium bicarbonate solution.

THEORY

pH is the measure of hydrogen ion concentration of a solution.
The hydrogen ion concentration (H+) for an acidic solution is always greater than 10-7 mol L-1 and its pH is, therefore, always less than 7.
The hydrogen ion concentration of a basic solution is always less than 10-7 mol L-1 and, therefore, its pH is always greater than 7.
The hydrogen ion concentration of a neutral solution is 10-7 mol L-1 and, therefore, its pH is 7.
The pH of a solution can be measured by using a pH paper, universal indicator or pH meter.
PROCEDURE

Take the given solutions in separate test tubes marked as A, B, C, D, E and F and keep them in the test tube stand.