Key Stage 3 Chemistry Quiz

The pH scale measures the acidity or alkalinity of a substance. A pH of 7 is considered neutral, while a pH below 7 is acidic and a pH above 7 is alkaline. A strong alkali is highly basic, therefore it would have a high pH value. The highest possible pH value on the scale is 14, indicating that the correct answer is 14.

Potassium is the most reactive metal among the four options given. This is because it belongs to Group 1 of the periodic table, known as the alkali metals. Alkali metals are highly reactive as they have only one valence electron, which they readily lose to form positive ions. Potassium reacts vigorously with water, oxygen, and many other substances. In contrast, silver, gold, and iron are less reactive metals, with silver and gold being relatively inert and iron being reactive but not as much as potassium.

A weak acid has a pH value less than 7. This is because a weak acid only partially dissociates in water, resulting in a lower concentration of hydrogen ions (H+) compared to a strong acid. The pH scale measures the acidity or alkalinity of a solution, with values below 7 indicating acidity. Therefore, a pH of 5 is a reasonable answer for the pH of a weak acid.

Bleach is not an example of a weak alkali. Bleach, which is commonly known as sodium hypochlorite, is a strong oxidizing agent and a strong base. It is used as a disinfectant and a cleaning agent due to its ability to break down organic matter and kill bacteria. Therefore, the correct answer is False.

The periodic table does not contain compounds, but rather it contains elements. Compounds are formed when two or more elements chemically combine together. The periodic table provides information about the elements, including their atomic number, symbol, and atomic weight.

An alkali could be used to treat a bee sting because alkalis are basic substances that can neutralize the acidic venom injected by the bee. The venom is acidic in nature, causing pain, swelling, and inflammation. Alkalis help to balance the pH level by neutralizing the acid, providing relief from the symptoms of the bee sting.

When an acid and alkali react together, they undergo a neutralization reaction. In this reaction, the acid donates a hydrogen ion (H+) to the alkali, forming water (H2O) as a product. At the same time, the alkali donates its hydroxide ion (OH-) to the acid, forming a salt. Therefore, the correct answer is "a salt and water."

A lemon is not an example of a strong acid. While lemons are acidic in nature, they are considered to be weak acids. Strong acids, on the other hand, completely dissociate in water and have a higher concentration of hydrogen ions. Lemons contain citric acid, which is a weak acid as it only partially dissociates in water. Therefore, the correct answer is false.

Distilled water, sodium chloride (table salt), and copper sulfate are considered neutral substances because they have a pH level close to 7, which is considered neutral on the pH scale. Vinegar, fairy liquid, and orange juice are acidic substances, while rain can be acidic or slightly alkaline depending on various factors.