Question 1: A pure substance contains only one type of particle, either atoms or molecules. It has a fixed composition and specific properties. Mixtures, on the other hand, consist of two or more substances that are physically combined but not chemically bonded.

Answer: A pure substance contains only one type of particle with a fixed composition and properties, unlike mixtures which are physically combined of multiple substances.

Question 2: Explain why a sample of pure water has a consistent boiling point of 100°C at standard atmospheric pressure.

Answer: Because pure water has a fixed chemical composition, it boils consistently at 100°C under standard conditions.

Question 1: List two common physical methods used to test the purity of a solid sample.

Answer: Melting point determination and chromatography.

Question 2: Describe a simple experiment to test the purity of a salt sample using melting point.

Answer: Heat the salt sample gradually and record the temperature at which it melts. A pure salt will melt at a specific, consistent temperature; impurities lower or broaden this melting point range.

Question 1: What does a narrow melting point range indicate about a substance's purity?

Answer: It indicates high purity, as the substance melts at a specific temperature without significant deviation.

Question 2: In chromatography, how can the presence of impurities in a sample be detected?

Answer: Impurities can be detected by additional spots or bands separate from the main substance's spot, indicating different components.

Question 1: A sample of salt is heated to determine its melting point. The pure salt melts at 801°C, but the sample melts over a temperature range of 797°C to 805°C. Calculate the percentage deviation from the pure melting point to assess its purity.

Answer: Percentage deviation = [(805 - 801) / 801] × 100 = 0.50%. The small deviation suggests the sample is quite pure.

Question 1: Why is purity crucial in the pharmaceutical industry, and how is it ensured?

Answer: Purity is crucial to ensure safety and effectiveness of medicines. It is ensured through rigorous testing like chromatography, melting point analysis, and spectroscopic methods.

Question 2: Describe a scenario where impurity in a fuel could cause problems in an engine.

Answer: Impurities such as sulfur compounds in fuel can lead to engine corrosion, clogging of filters, and increased emissions, reducing engine efficiency and lifespan.