Class 9 Science · 48 questions · 47 with answers
Which of the following correctly represents 360 g of water? (i) 2 moles of H20 (ii) 20 moles of water (iii) 6.022 × 1023 molecules of water (iv) 1.2044×1025 molecules of water
(d) (ii) and (iv)
(b) (i) and (iv)
(a) (i)
Which of the following statements is not true about an atom?
(a) Atoms are not able to exist independently
The chemical symbol for nitrogen gas is
(b) N2
The chemical symbol for sodium is
(d) Na
Which of the following would weigh the highest?
(c) 2 moles of CaCO3
(a) 0.2 mole of sucrose (C12 H22 O11)
(b) 2 moles of CO2
(d) 10 moles of H2O
Which of the following has maximum number of atoms?
(d) 18g of CH4
(a) 18g of H2O
(b) 18g of O2
(c) 18g of CO2
Which of the following contains maximum number of molecules?
(c) 1g H2
(a) 1g CO2
Mass of one atom of oxygen is 16 32
(a) g
3.42 g of sucrose are dissolved in 18g of water in a beaker. The number of oxygen atoms in the solution are
(a) 6.68 × 1023
A change in the physical state can be brought about
(c) when energy is either given to, or taken out from the system
Which of the following represents a correct chemical formula? Name it.
(b) BiPO4
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
Write the molecular formulae of all the compounds that can be formed by the combination of following ions Cu2+, Na+, Fe3+, C1–, S O 2- , PO 3- 4 4
CuCl2/ CuSO4/ Cu3 (PO4)2 NaCl/ Na2SO4/ Na3 PO4 FeCl3/ Fe2(SO 4)3 / FePO4
Write the cations and anions present (if any) in the following compounds
(a) CH3COONa
(b) NaCl
(c) H2
(d) NH4NO3 16-04-2018
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
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
Give the chemical formulae for the following compounds and compute the ratio by mass of the combining elements in each one of them. (You may use appendix-III).
(a) Ammonia
(b) Carbon monoxide
(c) Hydrogen chloride
(d) Aluminium fluoride (e) Magnesium sulphide
State the number of atoms present in each of the following chemical species
(a) CO32–
(b) PO43–
(c) P2O5
(d) CO
What is the fraction of the mass of water due to neutrons?
~ 8/18 Mass of one mole (Avogadro Number) of neutrons ~ 1 g Mass of one neutron = g Avogadro Number (N A ) Molar mass 18 Mass of one molecule of water = = g NA NA There are 8 neutrons in one atom of oxygen Mass of 8 neutrons = N Fraction of mass of water due to neutrons ~ ANSWERS 103
Does the solubility of a substance change with temperature? Explain with the help of an example.
Yes, it is a temperature dependent property. The solubility generally, increases with increase in temperature. For example, you can dissolve more sugar in hot water than in cold water.
Classify each of the following on the basis of their atomicity.
(a) F2
(b) NO2
(c) N2O
(d) C2H6 (e) P4 (f) H2O2 (g) P4O10 (H) O3 (i) HCl (j) CH4 (k) He (l) Ag
You are provided with a fine white coloured powder which is either sugar or salt. How would you identify it without tasting?
On heating the powder, it will char if it is a sugar. Alternatively, the powder may be dissolved in water and checked for its conduction of electricity. If it conducts, it is a salt.
Calculate the number of moles of magnesium present in a magnesium ribbon weighing 12 g. Molar atomic mass of magnesium is 24g mol–1. ATOMS AND MOLECULES 21 16-04-2018
Number of moles = = 0.5 mol Long Answer Questions
Verify by calculating that
(a) 5 moles of CO2 and 5 moles of H2O do not have the same mass.
(b) 240 g of calcium and 240 g magnesium elements have a mole ratio of 3:5.
Find the ratio by mass of the combining elements in the following compounds. (You may use Appendix-III)
(a) CaCO3
(b) MgCl2 (e) NH3
(c) H2SO4 (f) Ca(OH)2
(d) C2H5OH
Calcium chloride when dissolved in water dissociates into its ions according to the following equation. CaCl2 (aq) → Ca2+ (aq) + 2Cl– (aq) Calculate the number of ions obtained from CaCl2 when 222 g of it is dissolved in water.
1 mole of calcium chloride = 111g ∴ 222g of CaCl2 is equivalent to 2 moles of CaCl2 Since 1 formula unit CaCl2 gives 3 ions, therefore, 1 mol of CaCl2 will give 3 moles of ions 2 moles of CaCl2 would give 3×2=6 moles of ions. No. of ions = No. of moles of ions × Avogadro number = 6 × 6.022 ×10 23 = 36.132 ×10 23 = 3.6 132 ×1024 ions
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.
A sodium atom and ion, differ by one electron. For 100 moles each of sodium atoms and ions there would be a difference of 100 moles of electrons. Mass of 100 moles of electrons= 5.48002 g SLRVNNP Mass of 1 mole of electron = g SLRVNNP Mass of one electron = = 9.1 ×10 -28 g 100 × 6.022 ×1023 = 9.1×10-31 kg
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 mol–1 and 32 g mol–1 respectively.
Molar mass of HgS = 200.6 + 32 = 232.6 g mol–1 Mass of Hg in 232.6 g of HgS = 200.6 g Mass of Hg in 225 g of HgS 200.6 × 225 = 194.04g = PQPLT
The mass of one steel screw is 4.11g. Find the mass of one mole of these steel screws. Compare this value with the mass of the Earth (5.98 × 1024kg). Which one of the two is heavier and by how many times?
One mole of screws weigh = 2.475 ×1024g = 2.475×1021 kg Mass of the Earth 5.98 ×10 24 kg = = 2.4 ×103 Mass of 1 mole of screws 2.475 × 10 21 kg Mass of earth is 2.4×103 times the mass of screws The earth is 2400 times heavier than one mole of screws.
A sample of vitamic C is known to contain 2.58 ×1024 oxygen atoms. How many moles of oxygen atoms are present in the sample?
1 mole of oxygen atoms = 6.023×1023 atoms 2.58 ×1024 ∴Number of moles of oxygen atoms = 6.022 ×102 3 = 4.28 mol 4.28 moles of oxygen atoms.
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?
Fill in the missing data in the Table 3.1 Table 3.1 Species H2O CO2 Na atom MgCl2 Property No. of moles 2 — — 0.5 No. of particles — 3.011×10 23 — — Mass 36g — 115 g —
Species H2O CO2 Na atom MgCl2 Property No. of moles 2 0.5 5 0.5 No of particles 1.2044 ×1024 3.011×1023 3.011×1024 3.011×1023 Mass 36g 22g 115g 47.5g 102 2
The visible universe is estimated to contain 1022 stars. How many moles of stars are present in the visible universe? 16-04-2018
Number of moles of stars = 6.023 ×102 3 = 0.0166 mols
What is the SI prefix for each of the following multiples and submultiples of a unit?
(a) 103
(b) 10–1
(c) 10–2
(d) 10–6 (e) 10–9 (f) 10–12
Express each of the following in kilograms
(a) 5.84×10 -3 mg
(b) 58.34 g
(c) 0.584g
(d) 5.873×10 -21 g
Compute the difference in masses of 103 moles each of magnesium atoms and magnesium ions. (Mass of an electron = 9.1×10 –31 kg)
A Mg2+ ion and Mg atom differ by two electrons. 103 moles of Mg 2+ and Mg atoms would differ by 103 × 2 moles of electrons Mass of 2 ×103 moles of electrons = 2×103 × 6.023 ×1023 × 9.1 ×10–31 kg ⇒ 2×6.022 × 9.1×10 –5kg ⇒ 109.6004 ×10–5 kg ⇒ 1.096 × 10–3kg
Which has more number of atoms? 100g of N2 or 100 g of NH3
(i) 100 g of N2 = moles Number of molecules = × 6.022 ×1023 2 ×100 Number of atoms = × 6.022 ×10 23 = 43.01×1023 100 100 (ii) 100 g of NH3 = moles = × 6.022×1023 molecules 17 17 = × 6.022 ×1023 × 4 atoms = 141.69 ×1023 NH3 would have more atoms SLVS
Compute the number of ions present in 5.85 g of sodium chloride.
5.85 g of NaCl = = 0.1moles SVLS or 0.1 moles of NaCl particle Each NaCl particle is equivalent to one Na+ one Cl– ⇒ 2 ions Total moles of ions = 0.1 × 2 0.2 moles No. of ions= 0.2 × 6.022 ×1023 ⇒ 1.2042 ×1023 ions
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?
One gram of gold sample will contain = 0.9 g of gold Mass of gold Number of moles of gold = Atomic mass of gold 0.9 = = 0.0046 One mole of gold contains NA atoms = 6.022 ×1023 ∴ 0.0046 mole of gold will contain = 0.0046 × 6.022 ×1023 = 2.77×1021
What are ionic and molecular compounds? Give examples.
Atoms of different elements join together in definite proportions to form molecules of compounds. Examples— water, ammonia, carbondioxide. Compounds composed of metals and non-metals contain charged species. The charged species are known as ions. An ion is a charged particle and can be negatively or positively charged. A negatively charged ion is called an anion and the positively charged ion is called cation. Examples— sodium chloride, calcium oxide.
Compute the difference in masses of one mole each of aluminium atoms and one mole of its ions. (Mass of an electron is 9.1×10–28 g). Which one is heavier?
Mass of 1 mole of aluminium atom = the molar mass of aluminium = 27 g mol–1 An aluminium atom needs to lose three electrons to become an ion, Al3+ For one mole of A13+ ion, three moles of electrons are to be lost. The mass of three moles of electrons = 3 × (9.1×10–28 ) × 6.022×1023 g = 27.3 × 6.022 ×10–5 g = 164.400 ×10 –5 g = 0.00164 g Molar mass of Al 3+ = (27–0.00164) g mol–1 = 26.9984 g mol–1 Difference = 27 – 26.9984 = 0.0016 g ANSWERS 107
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.
Mass of silver = m g Mass of gold = g Mass Number of atoms of silver = × NA Atomic mass = × NA Number of atoms of gold = ×NA 100 ×197 Ratio of number of atoms of gold to silver = Au : Ag m m = × NA : × NA 100 ×197 108 = 108 : 100×197 = 108 : 19700 =1 : 182.41 16 g
A sample of ethane (C2H6) gas has the same mass as 1.5 ×1020 molecules of methane (CH4). How many C2H6 molecules does the sample of gas contain?
Mass of 1 molecule of CH4 = 1.5 × 1020 × 16 Mass of 1.5 ×1020 molecules of methane = g Mass of 1 molecule of C2H6 = g 1.5 × 1020 × 16 Mass of molecules of C2H 6 is = g 1.5 × 1020 × 16 NA ∴ Number of molecules of ethane = × = 0.8 × 10 20 NA 30
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 Ca3 (PO4)2 is ————.
(d) Formula of sodium carbonate is ———— and that of ammonium sulphate is ————. ATOMS AND MOLECULES 23 16-04-2018
Complete the following crossword puzzle (Fig. 3.1) by using the name of the chemical elements. Use the data given in Table 3.2. Table 3.2 Across Down 2. The element used by Rutherford 1. A white lustrous metal used for during his α–scattering making ornaments and which experiment tends to get tarnished black in 3. An element which forms rust on the presence of moist air exposure to moist air 4. Both brass and bronze are alloys 5. A very reactive non–metal stored of the element under water 6. The metal which exists in the 7. Zinc metal when treated with liquid state at room temperature dilute hydrochloric acid 8. An element with symbol Pb produces a gas of this element which when tested with burning splinter produces a pop sound. Fig. 3.1
This question refers to a figure in the original PDF.
46 (a) (b) Six : Helium (He); Neon ( Ne); Argon (Ar); Krypton (Kr); Xenon (Xe); Radon (Rn).
This question refers to a figure in the original PDF.
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
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 C6 H12 O6. 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 1 g cm–3. ATOMS AND MOLECULES 25 16-04-2018
6CO2 + 6 H2O Sunlight → C H O + 6O 6 12 6 2 1 mole of glucose needs 6 moles of water 180 g of glucose needs (6×18) g of water 1 g of glucose will need g of water. 18 g of glucose would need × 18 g of water = 10.8 g Mass 10.8 g Volume of water used = = =10.8 cm3 . Density 1g cm-3 C hapter 4 _lqucpq Multiple Choice Questions