Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Acids are substances that have a value less than . They typically have a sour taste and can be corrosive. In a lab, common acids include Hydrochloric acid () and Sulfuric acid ().
Alkalis are bases that dissolve in water and have a value greater than . They often feel soapy to the touch. A common laboratory alkali is Sodium hydroxide ().
Indicators are special chemicals used to test whether a substance is acidic, alkaline, or neutral by changing color.
Litmus paper is a common indicator. It comes in two types: Red litmus and Blue litmus.
In acidic conditions, blue litmus paper turns red, while red litmus paper stays red.
In alkaline conditions, red litmus paper turns blue, while blue litmus paper stays blue.
In neutral conditions (like pure ), red litmus stays red and blue litmus stays blue.
Neutralization is a chemical reaction where an acid reacts with an alkali to produce a salt and water, resulting in a solution closer to .
📐Formulae
💡Examples
Problem 1:
A scientist tests a clear liquid with red litmus paper. The paper changes from red to blue. What can the scientist conclude about the liquid?
Solution:
The liquid is an alkali.
Explanation:
Red litmus paper only changes color in the presence of an alkaline substance (where ). If the liquid were acidic or neutral, the red litmus would have remained red.
Problem 2:
What will happen to the color of blue litmus paper if it is dipped into a solution of Ethanoic acid ()?
Solution:
The blue litmus paper will turn red.
Explanation:
Since Ethanoic acid is an acid, it will cause the blue indicator dye in the litmus paper to shift to its acidic color, which is red.
Problem 3:
Complete the word equation for the reaction between Hydrochloric acid and Potassium hydroxide.
Solution:
Explanation:
This is a neutralization reaction. The 'Potassium' from the alkali and 'chloride' from the acid combine to form the salt, Potassium chloride (), along with water ().