Q. 5 g of calcium combine with 2 g of oxygen to form a compound. Find the molecular formula of the compound. (Atomic mass of Ca = 40 u; O = 16 u)
Ans. Number of moles in 5g of calcium = mass / molar mass = (5 / 40) = 0.125 Number of moles in 2g of oxygen = mass / molar mass = (2 / 16) = 0.125 Now we will calculate the simplest ratio of the element by dividing the number of moles of each element by the smallest value. Since number of moles of each element is 0.125, therefore calcium and oxygen are present in a ratio of 1 : 1. Thus the empirical formula of the compound is CaO. For calculating the molecular formula, we need the molecular mass of the compound. However, because a compound with the formula CaO is known, Therefore, the molecular formula of the compound is CaO. Q. (i) Name the body which approves the nomenclature of elements and compounds. (ii) The symbol of sodium is written as Na and not as S. Give reason. (iii) Name one element which form diatomic and one which form tetra atomic molecules. Ans. (i) IUPAC (International Union of Pure and Applied Chemistry) (ii) Latin name of sodium is Natrium. The first two letters (Na) of this name represents the symbol of sodium. (iii) Oxygen forms diatomic molecules and phosphorus forms tetra atomic molecules. Q. Calcium and Oxygen are combined in the rates of 5:4 by mass to form calcium oxide. What mass of Oxygen gas would be required to react with 2.5 g of calcium ? Ans: Calcium and oxygen combine in the rates of 5:4 by mass to form calcium oxide let x gram of oxygen is required to react with 2.5 g of calcium to form calcium oxide Therefore 5/4 = 2.5 / x then x = 2 Therefore 2 grams of oxygen is required to react with 2.5 grams of calcium to form calcium oxide .
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Q. A Tortoise A argues with argue with tortoise B according to A we weigh lens in water than Air but B oppose it. Who is correct A or B and which principal use by correct one?
Ans: Buoyant force is directly proportional to the density of fluid in which a solid is immersed. Water is much denser than air. So more buoyant force act in water Hence , Statement of A is correct. Q. What is reverberation? Write its one advantage and one disadvantage. How reverberation is reduced?
Ans: The repeated multiple reflections of sound in any big enclosed space, is called reverberation. When a sound is produced in a big hall, its wave reflects from the walls and travel back and forth. Due to this, energy does not reduce and the sound persists. Small amount of reverberation for lesser time helps in adding volume to the programmers. Too much reverberation confuses the programmers and must be reduced. To reduce reverberation, the roof and walls of the hall are covered with a sound absorbing material like rough plaster and thick curtains. Q. What is echo ranging? State any one application of this technique.
Echo ranging is the process of detecting underwater objects using sound signals. The minimum distance between source and the reflecting body should be 17 metres for the formation of an echo. This technique is used to measure depth of sea with the help of Sonar. Q. A person is listening to a tone of 500 Hz sitting at a distance of 450 m from the source of the sound. What is the time interval between successive compression from the source ? Ans. Here, f = 500 Hz The time interval between successive compression means the time period. T =1/f =1/500 = 0.002 s Explain the working and application of sonar. SONAR system consists of a transmitter and a detector and is installed on a ship or motorboat. The transmitter produces and transmits ultrasonic waves. These waves travel through water and strike the object under water on the sea bed. The object reflects these waves and is sensed by the detector. The detector converts the ultrasonic waves into electrical signals. If d be the depth of the said object and v be the velocity of the ultrasonic waves in water, then the time interval between transmission and reception of ultrasonic waves will be t = 2d/v By knowing the time t we can find the value of d. SONAR technique is used to determine the depth of the sea and to locate underwater hills, valleys, etc. Sonar, short for "Sound Navigation and Ranging," is a technology that uses sound waves to detect and locate objects underwater. It is a versatile and widely used system with both civilian and military applications. The principle of sonar is based on the transmission and reception of sound waves, which bounce off objects in the water and return to the source, allowing the system to analyze the data and provide valuable information about the underwater environment.
Working of Sonar:
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