Acids, Bases, and pH

• An acid is a substance with a pH value lower than 7.
• The closer the pH value is to 0, the stronger the acid.
• An alkali is a soluble base with a pH value higher than 7.
• The closer the pH value is to 14, the stronger the alkali.
• A base is a substance that reacts with an acid to neutralize it.
• A chemical reaction is a process involving the rearrangement of atoms to form new substances.
• An indicator is a substance that changes color when added to acidic or alkaline solutions.
• Litmus paper is a type of indicator paper used to test pH.
• Red litmus paper turns blue in alkaline solutions.
• Blue litmus paper turns red in acidic solutions.
• Litmus paper is bleached white in the presence of chlorine.
• A neutral substance has a pH value of 7.
• Neutralization is a reaction between an acid and a base or alkali, forming a salt and water.
• pH is a measure of the acidity or alkalinity of a substance on a scale of 0 to 14.
• A pH scale is a scale from 0 to 14 used to measure the acidity or alkalinity of a substance.
• A salt is a compound formed by the neutralization of an acid by a base.
• A universal indicator is a mixture of dyes that changes color gradually over a range of pH, used to test for acids and alkalis.

pH Scale

• The pH scale ranges from 0 to 14, with corresponding colors: red, scarlet, dark orange, orange, amber, yellow, lime green, green, green-blue, turquoise, blue, dark blue, indigo, violet, and purple.
• Substances with a pH between 0 and 6 are acidic, with those closer to 0 being more acidic.
• Substances with a pH of 7 are neutral.
• Substances with a pH between 8 and 14 are alkaline, with those closer to 14 being more alkaline.

Measuring pH

• pH can be measured using an indicator or a pH meter.
• Indicators change color when added to acidic, alkaline, or neutral solutions.
• pH meters provide a numerical value for pH.
• Some plants contain substances that can be used as indicators due to their color-changing properties.

Indicators

• Universal indicator changes color gradually over a range of pH values.
• Red litmus paper stays red in acidic solutions and turns blue in alkaline solutions.
• Blue litmus paper stays blue in acidic solutions and turns red in acidic solutions.

Dangers of Acids and Alkalis

• Hazard symbols warn about the dangers of substances.
• Corrosive substances can cause destruction of materials and burn the skin or damage the eyes.
• Substances that are a moderate health hazard may cause redness or blistering upon contact with the skin.
• The hazards depend on the type and concentration of the acid or alkali.
• Concentrated solutions have more acid or alkali particles in a given volume and are corrosive.
• Dilute solutions have fewer acid or alkali particles in a given volume and are often irritants (moderate health hazards).

Neutralization Reactions

• A neutralization reaction occurs between an acid and a base or alkali, forming a salt and water.
• acid + base → salt + water
• The pH gets closer to 7 as the acid and alkali are mixed, resulting in a neutral solution with the correct amounts.
• The type of salt produced depends on the acid and base that react.

Naming Salts

• The first part of the salt's name comes from the metal in the base taking part in the reaction.
• The second part of the salt's name comes from the acid taking part in the reaction.
• Hydrochloric acid produces chloride salts.
• Nitric acid produces nitrate salts.
• Sulfuric acid produces sulfate salts.

Making Salts

• Salts are produced in the lab using the following method.
• Use a measuring cylinder to measure the alkali into a beaker.
• Add drops of the acid from a pipette to the alkali and stir.
• Dip a stirring rod into the solution to take a small sample and check the pH by dotting it on a piece of universal indicator paper.
• Compare the color of the universal indicator paper with the universal indicator pH scale.
• Continue to add the acid and test the pH of the solution until a neutral pH result is obtained (pH 7 - green).
• Heat the neutral solution in an evaporating basin over a water bath until approximately 1/3 of the solution remains.
• Leave the remaining solution in a warm place to evaporate completely, then observe the remaining crystals.

Uses of Neutralization

• Acid rain can lower pH in soil and lakes, affecting the survival of plants and animals, but slaked lime (calcium hydroxide) can be added to increase pH.

Indigestion Tablets

• Indigestion tablets contain bases like magnesium hydroxide and magnesium carbonate that react with stomach acid, neutralizing it to form a salt and water.

Toothpaste

• Toothpaste contains alkalis like sodium hydrogen carbonate (sodium bicarbonate) to neutralize acid, preventing tooth decay from occurring.

Treating Stings

• Bee stings which are slightly acidic, can be neutralized using baking soda containing sodium hydrogen carbonate, which is alkaline.
• Wasp stings which are slightly alkaline, can be neutralized using vinegar which contains ethanoic acid.

Analysis and Evaluation

• A mean is calculated by adding a list of numbers and dividing by how many numbers are in the list.
• An anomalous result is a result that does not fit the pattern shown by other results.
• Anomalous results should be identified and omitted from the data before the mean is calculated.
• Scientific results are valid if the method ensures that the independent variable affects the dependent variable only.
• All other variables should be controlled.
• Results are repeatable if the same experimenter repeats the investigation using the same method and equipment and gets the same result.