1. Q. Why the symbol of iron is is Fe and sodium is Na? Ans: symbol of some have been taken from the names of elements in Latin, German or Greek. For example, the symbol of iron is Fe from its Latin name ferrum, sodium is Na from natrium. 2. Q. Mention the difference between N2 and 2N? Ans: N2 represent one molecules of nitrogen consist of two atoms and 2N represent two seprate atoms of nitrogen 3. Q. To identify the Law of Conservation of Mass, a student added 10 ml of 5% barium chloride solution into 10 ml of 5% sodium sulphate solution. Which one of the following is the correct observation? (a) A clear solution is formed (b) The solution turns to red colour (c) Yellow precipitate is formed (d) White precipitate is formed Hint: Aqueous solution of barium chloride reacts with that of sodium sulphate to form a white precipitate of barium sulphate. Ans: (d) 4. Q. To identify the Law of Conservation of Mass, a student added 10 ml of 5% barium chloride solution into 10 ml of 5% sodium sulphate solution. Which one of the following is the correct observation? (a) A clear solution is formed (b) The solution turns to red colour (c) Yellow precipitate is formed (d) White precipitate is formed Hint: Aqueous solution of barium chloride reacts with that of sodium sulphate to form a white precipitate of barium sulphate. Ans: (d) 5.Q. Define atomic number and mass number. Which one of them is a more fundamental attribute of element? State the reason. Ans: Atomic number is the total number of protons present in the nucleus of an atom. Mass number is the sum of protons and neutrons present in the nucleus of an atom. Atomic number is the fundamental attribute of elements because all elements are characterised by their atomic numbers. When elements react, their atoms either lose or gain electrons but their atomic number remains the same. 6.Q. A student noted down the following precautions for the experiment "To verify the law of conservation of mass in a chemical reaction" (i) Weighing should be done carefully. (ii) Flask should be corked tightly. (iii) Solutions should not get mixed before the reaction. (iv) Mixing of two solutions must be done quickly The precaution which needs to be corrected is: (a) (i) (b) (ii) (c) (iii) (d) (iv) Ans: (d) 7.Q. Nitrogen and Hydrogen atoms combine in the ratio 14 : 3 by mass to form ammonia molecule. Find the formulae of ammonia molecule by calculating the molar ratio. Ans: Atomic mass of 1-Nitrogen atom = 14 grams Atomic mass of 1- Hydrogen atom = 1 Nitrogen and hydrogen combine in the ratio 14: 3 by mass. Therefore one Nitrogen atom combines with three Hydrogen atoms and molecular weight of the compound formed is 17. The formulae of ammonia molecule = NH₃ (ammonia). 8. Q. Mention two advantages of Dalton’s atomic theory. Ans: two advantages of Dalton’s atomic theory
9.Q. Elaborate the basic difference between the formula unit mass and the molecular mass. Ans: The only difference is that we use the word formula unit for those substances whose constituent particles are ions. 10.Q. While searching for various atomic mass units, scientists initially took 1/16 of the mass of an atom of naturally occurring oxygen as the unit. State two reasons Ans: Scientists initially took 1/16 of the mass of an atom of naturally occurring oxygen as the unit because of following two reasons
Class 9 Atoms and molecules solved CBSE Papers New Class 9 Atoms and molecules solved CBSE Test Paper-1 Class 9 Atoms and molecules solved CBSE Test Paper-2 Class 9 Atoms and molecules solved CBSE Test Paper-3 Class 9 Atoms and molecules solved CBSE Test Paper-4 Class 9 Atoms and molecules solved CBSE Test Paper-5 Class 9 Atoms and molecules solved CBSE Test Paper-6 Download Files Questions Based on law of the conservation Lab Skil
0 Comments
9th physics Thrust and Pressure, Archimedes’ Principle, Relative Density key points The total force acting perpendicular on a given surface is called thrust. Thrust acting upon a unit area is called pressure. Its S.I. unit is Pascal denoted by ‘P’ Thus, pressure =Thrust/Area of contact Archimedes’ principle states that when a body is immersed partially or fully in a fluid, it experiences an upward force that is equal to the weight of the fluid displaced by it. Archimedes' Principle is used in designing ships and submarines. The Lacto meters and hydrometers used for measuring the purity of a sample of milk and for determining the density of the liquids are based on this principle. Buoyancy can be defined as the tendency of the fluid to exert an upward force on an object, which is wholly or partially immersed in a fluid. See full page 9th Science activity Biology for SA2 Activity: To study the features and draw diagrams of earthworm, cockroach, bony fish and bird.
9th Science activity Biology for SA2 Activity: To compare the external features of monocot and dicot plants
More use full link for physics study
Empirical formula and molecular formula CSE Class 9th Chemistry : Empirical formula :The empirical formula is the simplest formula for a compound in which atoms of different elements are present in simple ratio. It shows the relative number of atoms of each element. For example CH2O is the empirical formula of Glucose C6H12O6 Molecular formula : It is the formula in which the actual number of atoms of different element are present. For example, if the empirical formula of benzene is CH where as molecular formula is C6H6 , etc. An empirical formula is often calculated from elemental composition data. The weight percentage of each of the elements present in the compound is given by this elemental composition. Let's determine the empirical formula for a compound with the following elemental composition:40.00% C, 6.66% H, 53.34% O.
Empirical formula =C1H2O1 ; Empirical formula mass = 12 + 2x1 +16 = 30 a.m.u Given relative molecular mass = 180 Divide the relative molecular mass by the Empirical formula mass to find a multiple: 180/30 = 6 The molecular formula is a multiple of 6 times the empirical formula: (C1H2O1)x6 = C6H12O6 EMPIRICAL AND MOLECULAR FORMULAE WORKSHEET 1.Whatâs the empirical formula of a molecule containing 65.5% carbon, 5.5% hydrogen, and 29.0% oxygen? 2. If the molar mass of the compound in problem 1 is 110 grams/mole, whatâs the molecular formula?
3 Whatâs the empirical formula of a molecule containing 18.7% lithium, 16.3% carbon, and 65.0% oxygen? 4. If the molar mass of the compound in problem 3 is 73.8 grams/mole, whatâs the molecular formula? 5.The percentage composition of acetic acid is found to be 39.9% C, 6.7% H, and 53.4% O. Determine the empirical formula of acetic acid. 6. The molar mass for question #9 was determined by experiment to be 60.0 g/mol. What is the molecular formula? 7. A 50.51 g sample of a compound made from phosphorus and chlorine is decomposed. Analysis of the products showed that 11.39 g of phosphorus atoms were produced. What is the empirical formula of the compound? 8. When 2.5000 g of an oxide of mercury, (HgxOy) is decomposed into the elements by heating, 2.405 g of mercury are produced. Calculate the empirical formula. 9.The compound benzamide has the following percent composition. What is the empirical formula? C = 69.40 % H= 5.825 % O = 13.21 % N= 11.57 % 10.A component of protein called serine has an approximate molar mass of 100 g/mole. If the percent composition is as follows, what is the empirical and molecular formula of serine? C = 34.95 % H= 6.844 % O = 46.56 % N= 13.59 % Answer. 1. C3H3O mass = 55 g/mole 2. C6H6O2 3 Li2CO3 4 Li2CO3 5. CH2O 6. C2H4O2 7. PCl3 8. Hg2O 9. C7H7NO 10. C3H7NO3 empirical formula , C3H7NO3 molecular formula
|
Blog SeaRCH Link
All
Join Us For Update |