1.
Rusting of an article made up of iron is called ____________.
Correct Answer
C. Corrosion, and it is a chemical change
Explanation
Rusting of an article made up of iron is called corrosion. Corrosion is a chemical change because it involves a reaction between iron and oxygen in the presence of water or moisture, leading to the formation of iron oxide (rust). This process is not reversible and results in the degradation and deterioration of the iron article.
2.
Which of the following statements is true for pure substances?
- Pure substances contain only one kind of particle.
- Pure substances may be compounds or mixtures.
- Pure substances have the same composition throughout.
- Pure substances can be exemplified by all elements other than nickel.
Correct Answer
B. A) and c)
Explanation
Pure substances contain only one kind of particle, meaning that all particles within the substance are the same. This is true for both elements and compounds. Additionally, pure substances have the same composition throughout, meaning that the proportion of different particles remains constant. Therefore, the correct statements are a) and c).
3.
Which of the following provides an example of a true solution?
Correct Answer
D. Sugar solution
Explanation
A true solution is a homogeneous mixture where the solute particles are evenly dispersed and cannot be seen with the naked eye. Blood is not a true solution as it contains cells and other particles that can be seen. Milk is also not a true solution as it is a colloidal suspension, meaning it contains larger particles that can be seen under a microscope. Starch solution is not a true solution as it contains suspended starch particles (starch particles are large and do not dissolve completely in water, making starch solutions cloudy). However, sugar solution is a true solution as the sugar molecules are dissolved in the solvent (usually water) and cannot be seen.
4.
The mass percent concentration of solution is the mass of the solute in grams, which is present in _______________.
Correct Answer
D. 100 gm of solution
Explanation
The mass percent concentration of a solution is determined by the mass of the solute present in a given amount of solvent. In this case, the correct answer is 100 gm of solution, as it specifies the amount of solvent (100 gm) in which the solute is dissolved to determine the mass percent concentration.
5.
A solution, which at a given temperature dissolves as much solute as it is capable of dissolving, is said to be a ________________.
Correct Answer
A. Saturated solution
Explanation
A saturated solution is a solution that has dissolved as much solute as it can at a given temperature. This means that no more solute can be dissolved in the solution without changing the temperature or pressure.
6.
A mixture of sand in water is an example of a/an ___________.
Correct Answer
C. Suspension
Explanation
A suspension is a heterogeneous mixture in which solid particles are dispersed in a liquid and can be seen with the naked eye. In the case of sand in water, the sand particles do not dissolve in the water but instead remain suspended, giving the mixture a cloudy appearance. This is different from a true solution, where the solute particles are evenly distributed and cannot be seen, and a colloidal solution, where the solute particles are larger than in a true solution but smaller than in a suspension. Therefore, the correct answer is suspension.
7.
Which one of the following shows the Tyndall effect?
Correct Answer
B. Milk
Explanation
Milk shows the Tyndall effect because it is a colloidal suspension of fat globules in water. When light passes through milk, the particles scatter the light, making the path of the light visible. This scattering of light is known as the Tyndall effect. Salt solution, copper sulfate solution, and starch solution do not show the Tyndall effect as they do not contain particles large enough to scatter light.
8.
Tincture of iodine has antiseptic properties. This solution is made by dissolving __________.
Correct Answer
D. Iodine in alcohol and water
Explanation
Tincture of iodine is a solution that is commonly used as an antiseptic. It is made by dissolving iodine in alcohol and water. Alcohol is used as a solvent because it helps to dissolve the iodine and allows for easy application onto the skin or wounds. The iodine in the tincture acts as an antiseptic by killing or inhibiting the growth of microorganisms, making it an effective solution for disinfection purposes.
9.
Which of the following is/are physical changes?
- Melting of iron metal
- Rusting of iron
- Bending of an iron rod
- Drawing a wire of iron metal
Correct Answer
C. A) c) d)
Explanation
The melting of iron metal is a physical change because it involves a change in state from solid to liquid without altering the chemical composition of the substance. Bending of an iron rod is also a physical change as it involves a change in shape without any change in the chemical composition. Drawing a wire of iron metal is also a physical change as it involves stretching and shaping the metal without altering its chemical composition. Rusting of iron, however, is a chemical change as it involves the reaction of iron with oxygen in the presence of water, resulting in the formation of iron oxide.
10.
Which of the following is/are chemical changes?
- decaying of wood
- burning of wood
- sawing of wood
- Hammering a nail into a piece of wood
Correct Answer
A. A) b)
Explanation
Decaying of wood and burning of wood are both examples of chemical changes. Decaying involves the breakdown of organic matter by microorganisms, resulting in the release of gases and the formation of new compounds. Burning wood involves the rapid oxidation of wood in the presence of oxygen, leading to the production of heat, light, and new substances like ash and smoke. The sawing of wood and the hammering of a nail into a piece of wood, however, are physical changes as they do not involve the formation of new substances or a change in the chemical composition of the wood.
11.
Air is regarded as a _________.
Correct Answer
B. Mixture
Explanation
Air is considered a mixture because it is composed of various gases such as nitrogen, oxygen, carbon dioxide, and trace amounts of other gases. These gases are not chemically combined, meaning they can be separated by physical means such as filtration or distillation. Additionally, the composition of air can vary depending on location and environmental factors, further supporting the idea that it is a mixture rather than a compound or element.
12.
Which of the following statements is not true about a true solution?
Correct Answer
C. At constant temperature, particles of solute settle down.
Explanation
True solutions are homogeneous in nature, meaning that the solute particles are evenly distributed throughout the solvent. They are so small that they cannot be filtered out using filter paper. Additionally, true solutions are stable and do not separate into their individual components over time. However, the statement "At constant temperature, particles of solute settle down" is not true for true solutions. In a true solution, the solute particles are uniformly dispersed and do not settle out, even at constant temperature.
13.
Butter can be separated from curd by _____________.
Correct Answer
A. Centrifugation
Explanation
Centrifugation is a process that involves spinning a mixture at high speeds to separate its components based on their density. In the case of separating butter from curd, centrifugation can be used because butter is less dense than curd. By subjecting the mixture to centrifugal force, the denser curd will settle at the bottom while the lighter butter will rise to the top, allowing for easy separation.
14.
The crystallization method cannot be used to purify those mixtures which​ _______________.
Correct Answer
D. Either decompose or get charred on heating to dryness, that is, cannot be separated by evaporation.
Explanation
The crystallization method is a technique used to purify mixtures by allowing the formation of pure crystals. It relies on the solubility of the impurities in the mixture, as the solvent is heated and then cooled to form crystals. However, if some impurities are soluble and cannot be separated by filtration, the crystallization method would not be effective in purifying the mixture. Therefore, the correct answer is that the mixture can be separated by filtration, as some impurities are insoluble.
15.
Two chemical species, X and Y, combine together to form a product P, which contains both X and Y.
X + Y -------------------P
X and Y cannot be broken down into simpler substances by simple chemical reactions. Which of the following concerning the species X, Y, and P are correct
- P is compound
- X and Y are compounds
- X and Y are elements
- P has a fixed composition
Correct Answer
D. I, iii and iv
Explanation
The correct answer is i, iii and iv. This is because the statement i is correct as P is formed by the combination of X and Y, indicating that it is a compound. The statement iii is correct as X and Y cannot be broken down into simpler substances, indicating that they are elements. The statement iv is correct as P has a fixed composition, meaning that it always contains both X and Y in a specific ratio.