Free Ncert Solutions for 9th Class Science Atoms and Molecules - Studyadda.com

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9th Science Atoms and Molecules

1)

In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium ethanoate. Show that the observations are in agreement with the law of conservation of mass. Sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
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2)

Hydrogen and oxygen combine in the ratio of 1 : 8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?
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3)

Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?
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4)

Which postulate of Dalton's atomic theory can explain the law of definite proportions?
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5)

Define the atomic mass unit.
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6)

Why is it not possible to see an atom with naked eyes?
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7)

Write down the formulae of (i) sodium oxide, (ii) aluminium chloride, (iii) sodium sulphide, (iv) magnesium hydroxide.
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8)

Write down the names of compounds represented by the following formulae: (i)Al2(SO4)3 (ii)CaCl2 (iii)K2SO4 (iv)KNO3 (v)CaCO3
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9)

What is meant by the term chemical formulae?
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10)

How many atoms are present in a (i) H2S molecule and (ii) PO43- ion?
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11)

Calculate the molecular masses of H2, O2, Cl2, CO2, CH4, C2H6, C2H4, NH3, CH3OH.
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12)

Calculate the formula unit masses of ZnO, Na2O, K2CO3. Given atomic masses of Zn = 65 u, Na = 23 u, K= 39 u, C =12 u and O = 16 u.
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13)

If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
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14)

Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given atomic mass of Na = 23 u, Fe = 56 u) ?
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15)

A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.
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16)

When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is burnt in 50.00 g of oxygen ? Which law of chemical combination will govern your answer?
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17)

What are polyatomic ions? Give examples.
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18)

Write the chemical formulae of the following: (a) Magnesium chloride (b) Calcium oxide (c) Copper nitrate (d) Aluminium chloride (e) Calcium carbonate
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19)

Give the names of the elements present in the following compounds. (a) Quick lime (b) Hydrogen bromide (c) Baking powder (d) Potassium sulphate
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20)

Calculate the molar mass of the following substances. (a) Ethyne, C2H2 (b) Sulphur molecule, S8 (c) Phosphorus molecule, P4 (atomic mass of phosphorus = 31) (d) Hydrochloric acid, HCl (e) Nitric acid, HNO3.
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21)

What is the mass of (a) 1 mole of nitrogen atoms? (b) 4 moles of aluminium atoms (atomic mass of aluminium = 27)? (c) 10 moles of sodium sulphite (Na2SO3) ?
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22)

Convert into mole. (a) 12 g of oxygen gas (b) 20 g of water (c) 22 g of carbon dioxide
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23)

What is the mass of (a) 0.2 mole of oxygen atoms? (b) 0.5 mole of water molecules?
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24)

Calculate the number of molecules of sulphur (S8) present in 16 g of solid sulphur?
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25)

Calculate the number of aluminium ions present in 0.051 g of aluminium oxide. (Hint: The mass of an ion is the same as that of an atom of the same element. Atomic mass of Al = 27 u)
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26) Which of the following correctly represents 360 g of water? (i) 2 moles of (ii) 20 moles of water (iii) 6.022 x 1023 molecules of water (iv) 1.2044 x 1025 molecules of water (a) only (i) (b) (i) and (iv) (c) (ii) and (iii) (d) (ii) and (iv)
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27) Which of the following statements is not true about an atom? (a) Atoms are not able to exist independently (b) Atoms are the basic units from which molecules and ions are formed (c) Atoms are always neutral in nature (d) Atoms aggregate in large numbers to form the matter that we can see, feel or touch
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28) The chemical symbol for nitrogen gas is (a) Ni (b) (c) (d) N
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29) The chemical symbol for sodium is (a) So (b) Sd (c) NA (d) Na
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30) Which of the following would weigh the highest? (a) 0.2 mole of sucrose (b) 2 moles of (c) 2 moles of (d) 10 moles of
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31) Which of the following has maximum number of atoms? (a) 18 g of (b) 18 g of (c) 18 g of (d) 18 g of
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32) Which of the following contains maximum number of molecules? (a) (b) (c) (d)
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33) Mass of one atom of oxygen is (a) (b) (c) (d) 8 u
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34) 3.42 g of sucrose are dissolved in 18 g of water in a beaker. The number of oxygen atoms in the solution are (a) 6.68 x1023 (b) 6.09 x1022 (c) 6.022 x 10 (d) 6.022 x1021
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35) A change in the physical state can be brought about (a) only when energy is given to the system (b) only when energy is taken out from the system (c) when energy is either given to, or taken out from the system (d) without any energy change
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36) Which of the following represents a correct chemical formula? Name it. (a) CaCI (b) (c) (d) NaS
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37) Write the molecular formulae for the following compounds (a) Copper (II) bromide (b) Aluminium (III) nitrate (c) Calcium (II) phosphate (d) Iron (III) sulphide (e) Mercury (II) chloride (f) Magnesium (II) acetate
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38) Write the molecular formulae of all the compounds that can be formed by the combination of following ions.
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39) Write the cat ions and anions present (if any) in the following compounds. (a) (b) (c) (d)
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40) Give the formulae of the compounds formed from the following sets of elements. (a) Calcium and fluorine (b) Hydrogen and sulphur (c) Nitrogen and hydrogen (d) Carbon and chlorine (e) Sodium and oxygen (f) Carbon and oxygen
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41) Which of the following symbols of elements are incorrect? Give their correct symbols. (a) Cobalt CO (b) Carbon c (c) Aluminium AL (d) Helium He (e) Sodium So
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42) Give the chemical formulae for the following compounds and compute the ratio by mass of the combining elements in each one of them. (a) Ammonia (b) Carbon monoxide (c) Hydrogen chloride (d) Aluminium fluoride (e) Magnesium sulphide
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43) State the number of atoms present in each of the following chemical species (a) (b) (c) (d)
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44) What is the fraction of the mass of water due to neutrons?
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45) Does the solubility of a substance change with temperature? Explain with the help of an example.
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46) Classify each of the following on the basis of their atomicity. (a) (b) (c) (d) (e) (f) (g) (h) (i) HCI (j) (k) He (I) Ag
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47) You are provided with a fine white coloured powder which is either sugar or salt. How would you identify it without testing?
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48) Calculate the number of moles of magnesium present in a magnesium ribbon weighing 12g. Molar atomic mass of magnesium is 24 g .
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49) Verify by calculating that (a) 5 moles of and 5 moles of do not have the same mass. (b) 240 g of calcium and 240 g magnesium elements have a mole ratio of 3 : 5.
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50) Find the ratio by mass of the combining elements in the following compounds. (a) (b) (c) (d) (e) (f)
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51) Calcium chloride when dissolved in water dissociates into its ions according to the following equation. Calculate the number of ions obtained from when 222 g of it is dissolved in water.
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52) The difference in the mass of 100 moles each of sodium atoms and sodium ions is 5.48002 g. Compute the mass of an electron.
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53) Cinnabar (HgS) is a prominent ore of mercury. How many grams of mercury are present in 225 g of pure HgS? Molar mass of Hg and S are 200.6 g and 32g respectively.
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54) The mass of one steel screw is 4.11 g. Find the mass of one mole of these steel screws. Compare this value with the mass of the earth (5.98 x 1024 kg). Which one of the two is heavier and by how many times?
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55) A sample of vitamin C is known to contain 2.58 x 1024 oxygen atoms. How many moles of oxygen atoms are present in the sample?
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56) Raunak took 5 moles of carbon atoms in a container and Krish also took 5 moles of sodium atoms in another container of same weight. (a) Whose container is heavier? (b) Whose container has more number of atoms?
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57) Fill in the missing data in the following table.

Species property Na-atom

Number of particles 2 - - 0.5

Number of particles - - -

Mass 36 g - 115 g -

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58) The visible universe is estimated to contain 1022 stars. How many moles of stars are present in the visible universe?
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59) What is SI prefix for each of the following multiples and submultiples of a unit? (a) 103 (b) (c) (d) (e) (f)
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60) Express each of the following in kilograms (a) (b) 58.34 g (c) 0.584 g (d)
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61) Compute the difference in masses of 103 moles each of magnesium atoms and magnesium ions. (Mass of an electron )
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62) Which has more number of atoms? 100 g of N3 or 100 g of
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63) Compute the number of ions present in 5.85 g of sodium chloride.
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64) A gold sample contains 90% of gold and the rest copper. How many atoms of gold are present in one gram of this sample of gold?
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65) What are ionic and molecular compounds? Give examples.
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66) Compute the difference in masses of one mole each of aluminium atoms and one mole of its ions (Mass of an electron is ). Which one is heavier?
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67) A silver ornament of mass 'm' gram is polished with gold equivalent to 1% of the mass of silver. Compute the ratio of the number of atoms of gold and silver in the ornament.
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68) A sample of ethane gas has the same mass as 1.5 x 1020 molecules of methane . How many molecules does the sample of gas contain?
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69) Fill in the blanks. (a) In a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is called ......... , (b) A group of atoms carrying a fixed charge on them is called ......... . (c) The formula unit mass of is??. (d) Formula of sodium carbonate is ......... and that of ammonium sulphate is ......... .
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70) Complete the following crossword puzzle (figure) by using the name of the chemical elements. Use the data given in table following.

Across Down

2. The element used by Rutherford during his a- scattering experiment. 1. A white lustrous metal used for making ornaments and which tends to get tarnished black in the presence of moist air.

3. An element which forms rust on exposure to moist air. 4. Both brass and bronze are alloys of the element.

5. A very reactive non-metal stored under water. 6. The metal which exists in the liquid state at room temperature.

7. Zinc metal when treated with dilute hydrochloric acid produces a gas of this element which when tested with burning splinter produces a pop sound. 8. An element with symbol Pb.

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71) (a) In this crossword puzzle (Figure), names of 11 elements are hidden. Symbols of these are given below. Complete the puzzle. 1. Cl 2. H 3. Ar 4. 0 5. Xe 6. N 7. He 8. F 9. Kr 10. Rn 11. Ne (b) Identify the total number of inert gases, their names and symbols from this cross ward puzzle.
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72) Write the formulae for the following and calculate the molecular mass for each one of them. (a) Caustic potash (b) Baking powder (c) Lime stone (d) Caustic soda (e) Ethanol (f) Common salt
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73) In photosynthesis, 6 molecules of carbon dioxide combine with an equal number of water molecules through a complex series of reactions to give a molecule of glucose having a molecular formula . How many grams of water would be required to produce 18 g of glucose? Compute the volume of water so consumed assuming the density of water to be .
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