Question 1: Define a pure substance in your own words.

Answer: A pure substance is a material made up of only one type of particle, either an element or a compound, with a uniform composition throughout.

Question 2: Explain how a pure substance differs from a mixture.

Answer: A pure substance has a fixed composition and consists of only one type of particle, while a mixture contains two or more different substances that are not chemically bonded and can vary in proportion.

Question 3: Which of the following is a pure substance? a) Saltwater b) Elemental oxygen c) Air d) Salad

Answer:

Question 1: Name two laboratory methods used to assess the purity of a chemical substance.

Answer: Chromatography and melting point analysis are common methods used to test purity.

Question 2: Describe how measuring the melting point of a substance can indicate its purity.

Answer: A pure substance has a specific melting point; deviations or broadening of this point suggest impurities.

Question 1: A sample of salt weighing 50 grams contains 45 grams of pure salt. Calculate the percentage purity of the salt sample.

Answer: Percentage purity = (Mass of pure substance / Total mass of sample) × 100 = (45 g / 50 g) × 100 = 90%

Question 2: A solution contains 10 grams of sugar dissolved in 250 mL of water. What is the concentration of sugar in grams per liter (g/L)?

Answer: Concentration = (Mass of solute / Volume of solution) = (10 g / 0.250 L) = 40 g/L

Question 1: Design a simple experiment to test whether a sample of water is pure. Include the key variables and safety precautions.

Answer: To test water purity, measure its boiling point and compare it to the expected boiling point of pure water (100°C at standard pressure). Variables include temperature and atmospheric pressure. Use a clean, calibrated thermometer and ensure the sample is free from contaminants. Safety precautions include handling hot equipment carefully and working in a well-ventilated area.

Question 2: Explain why impurities in a substance can affect its melting point and how this can be used to assess purity.

Answer: Impurities disrupt the orderly structure of a substance, lowering or broadening its melting point range. A pure substance melts sharply at a specific temperature, so deviations indicate impurities.

Question 1: Why is it important to have pure water in medical applications?

Answer: Pure water is essential in medical applications to prevent contamination, infections, and ensure accurate results in experiments or treatments.

Question 2: Describe how the pharmaceutical industry ensures the purity of medicines.

Answer: The pharmaceutical industry uses rigorous testing methods such as chromatography, spectrometry, and purity analysis to ensure medicines meet strict purity standards. They also follow Good Manufacturing Practices (GMP) to minimize contamination and verify the chemical composition of active ingredients.