Very Short Question Answer: Nature of Matter: Elements, Compounds, and Mixtures

Q1: What is a homogeneous mixture of two or more substances called?
Ans: A solution is a homogeneous mixture of two or more substances. In a solution the composition is uniform throughout, the solute is dissolved in the solvent and the different components cannot be distinguished by the eye. Example: salt dissolved in water forms a solution.

Q2: What is an element made up of?
Ans: An element is made up of only one type of atom. For example: Carbon (C), Iron (Fe). An element cannot be broken down into simpler substances by ordinary chemical methods.

Q3: Name two categories of pure substances.
Ans: Element and compound. An element contains only one kind of atom, while a compound contains two or more elements chemically combined in a fixed ratio.

Q4: What are two types of matter on the basis of composition?
Ans: Pure substances and mixtures are the two main types of matter based on composition. Pure substances have a definite, fixed composition, whereas mixtures have variable composition and the components retain their individual properties.

Q5: Name the types of mixtures.
Ans: The two types of mixtures are homogeneous and heterogeneous mixtures. In homogeneous mixtures the components are uniformly distributed; in heterogeneous mixtures they are not.

Q6: Give natural examples of a mixture.
Ans: Examples of natural mixtures include seawater (water with dissolved salts), mineral ores (rocks containing several minerals), and soil (a mixture of organic matter, minerals and air).

Q7: Name a metal that is liquid at room temperature.
Ans: Mercury is the only metal that is liquid at normal room temperature. It is dense and conducts electricity, which led to its former use in thermometers; however, its use is now limited because it is toxic.

Q8: What is the principle of separation?
Ans: The principle of separation is based on differences in physical or chemical properties such as boiling point, solubility, density or particle size. For example, distillation uses different boiling points, filtration uses particle size, and evaporation uses differences in volatility.

Q9: Give an example of a liquid and a liquid-type solution.
Ans: Vinegar is a solution made from a mixture of acetic acid and water. Here acetic acid is the solute and water is the solvent, and the mixture is uniform throughout.

Q10: Define the term heterogeneous mixture.
Ans: A mixture where components are not uniformly distributed and properties vary is called heterogeneous. Examples include oil mixed with water, and a mixture of sand and iron filings.

Q11: What is a mixture, and how do its components retain their properties?
​Ans: A mixture is two or more substances combined physically where each substance retains its own properties because no chemical reaction takes place. The components can usually be separated by physical methods such as filtration, evaporation or magnetism.

Q12: Name two examples of uniform mixtures mentioned in the chapter.
​Ans: Sugar dissolved in water (sugar-water) and air are examples of uniform (homogeneous) mixtures. In both cases the components are evenly distributed throughout.

Q13. What happens when lime water is exposed to air, and why does it turn milky?
​Ans: Lime water turns milky because carbon dioxide from the air reacts with calcium hydroxide in lime water to form calcium carbonate, which is a white precipitate. The reaction is: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O.

Q14. What are the two gases produced when electricity is passed through water, and how can they be identified?
​Ans: Hydrogen and oxygen are produced. Hydrogen can be identified by a lighted splint producing a characteristic 'pop' sound, and oxygen can be identified because it makes a glowing splint burn more brightly.

Q15. Why is water considered a compound and not a mixture?
​Ans: Water is a compound because hydrogen and oxygen are chemically combined in a fixed ratio of 2:1 to form molecules of water (H₂O). Its properties are different from those of hydrogen and oxygen, and its elements cannot be separated by physical methods.

Q16. What is the difference between the properties of iron sulfide (Sample B) and the mixture of iron and sulfur (Sample A)?
​Ans: Iron sulfide (Sample B) is a chemical compound and shows new properties: it is non-magnetic and reacts with dilute acid to produce hydrogen sulfide gas (H₂S, which smells of rotten eggs). The mixture of iron and sulfur (Sample A) is a physical mixture, so it is magnetic (because of the iron) and does not produce H₂S on adding acid until a chemical reaction forms iron sulfide.

Q17. Name two alloys mentioned in the chapter and their constituent elements.
​Ans: Brass (an alloy of copper and zinc) and bronze (an alloy of copper and tin).

Q18. What are native minerals, and give two examples of them from the chapter.
​Ans: Native minerals are elements that occur in nature in their pure, native form. Examples from the chapter are gold and sulfur.

Q19. Why can't the elements in sodium chloride be separated by physical methods?
​Ans: In sodium chloride (NaCl) the elements sodium and chlorine are chemically bonded to form an ionic compound in a fixed ratio. Because they are chemically combined, they cannot be separated by physical methods and require chemical processes to be separated into elements.

Q20. What is observed when sugar is heated, and what does this indicate about its composition?
​Ans: When sugar is heated it first melts and then turns brown (caramelises) and finally chars to form black carbon. Water droplets are also observed as moisture is driven off. These changes show that sugar is a compound made of carbon, hydrogen and oxygen, and it undergoes chemical change on strong heating.