Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Acids are substances that have a pH value less than . They often have a sour taste and turn blue litmus paper red.
Alkalis are bases that are soluble in water. They have a pH value greater than , feel soapy to the touch, and turn red litmus paper blue.
The pH scale is a numerical range from to used to measure how acidic or alkaline a solution is. A pH of is considered neutral ().
Indicators are substances that change color depending on the pH. Universal Indicator provides a spectrum of colors: red/orange for acids, green for neutral, and blue/purple for alkalis.
Neutralization is a chemical reaction where an acid reacts with an alkali to produce a neutral solution of salt and water. The ions from the acid react with ions from the alkali.
Common laboratory acids include Hydrochloric acid () and Sulfuric acid (). A common alkali is Sodium hydroxide ().
📐Formulae
💡Examples
Problem 1:
A student tests a solution of lemon juice using Universal Indicator and observes a dark orange color. Estimate the pH and classify the substance.
Solution:
pH to ; Strong/Medium Acid.
Explanation:
Lemon juice contains citric acid. On the Universal Indicator color chart, orange corresponds to a pH of approximately or , indicating it is an acidic substance.
Problem 2:
What is the resulting pH when a strong acid like is mixed in exact proportions with a strong alkali like ?
Solution:
pH
Explanation:
This is a neutralization reaction. The hydrogen ions () and hydroxide ions () combine to form water (), which is neutral, resulting in a pH of .
Problem 3:
Identify the ions responsible for acidity and alkalinity in aqueous solutions.
Solution:
Acidity: ions; Alkalinity: ions.
Explanation:
Acids release hydrogen ions () when dissolved in water, while alkalis release hydroxide ions () in solution.