Atoms And Molecules

(ii) and (iv) options correctly represent 360g of water.

(ii) 1 mole of water = molar mass of water = 18g

Thus, 20 moles of water = 18g x 20 = 360g

(iv) 1 mole of water = 6.022 x 10²³ molecules of water = 18g of water

Thus, 1.2044×10²⁵ molecules of water =

= 360g

Atoms form molecules and ions. These molecules or ions aggregate in large numbers to form the matter that we can see, feel or touch. Atoms are always neutral in nature.

The chemical symbol for nitrogen gas is N_2.

The chemical symbol for sodium is Na. N being in capital letter and “a” being in small letter.

Mass of given sample = Molar mass X number of moles

m = M X N

(a) 0.2 moles of sucrose (C₁₂H₂₂O₁₁):

Molar mass of sucrose (C₁₂H₂₂O₁₁) = 342g/mole

Thus, the mass of 0.2 moles of sucrose (C₁₂H₂₂O₁₁) = 342 X 0.2

= 68.4g

(b) 2 moles of CO₂ = 2×44 = 88g

(c) 2 moles of CaCO₃ = 2×100 = 200 g

(d) 10 moles of H₂O = 10×18 = 180

Thus, the mass of 0.2 moles of sucrose (C₁₂H₂₂O₁₁) would weigh the highest.

18g of CH₄ contains a maximum number of atoms.

Molar mass of CH₄ = The atomic mass of C + 4 X the atomic mass of H

= 12 + 4

= 16g

Number of atoms = 1 + 4 = 5

Thus,

Number of atoms = Number of atoms in the molecule×

=

= 5.63 N_A

The number of atoms in 18g of H₂O :

Molar mass of H₂O = 18g; Number of atoms = 2 + 1 = 3

=

= 3 N_A

The number of atoms in 18g of O₂:

Molar mass of O₂ = 32g; Number of atoms in O₂ = 1 + 1 = 2

=

= 1.12 N_A

The number of atoms in 18g of CO₂ :

Molar mass of CO₂ = 44g;

=

= 1.23 N_A

1g H₂ contains a maximum number of molecules.

The molecules present in the 1g CO₂:

Molar mass of CO₂ = 44g

The number of molecules

=

= 0.02N_A

The molecules present in the 1g N₂ :

Molar mass of N₂ = 28g

The number of molecules

=

= 0.03N_A

The molecules present in the 1g H₂ :

Molar mass of N₂ = 2g

=

= 0.5N_A

The molecules present in the 1g CH₄ :

Molar mass of CH₄ = 16g

=

= 0.06N_A

Thus, we can see that 1g H₂ contains the highest number of molecules.

Molecular mass of oxygen = 16g

6.023x10²³ atoms of oxygen have mass = 16g

1 atom of oxygen has mass =

Molar mass of sucrose (C₁₂ H₂₂ O₁₁) = 342g/mole

Thus,

Number of moles of sucrose = Given mass/ Molar Mass

=

1 mol of sucrose contains = 1× N_A sucrose molecules = 11 x N_A atoms of oxygen

0.01 mol of sucrose (C₁₂ H₂₂ O₁₁) contains = 0.01 × 11 × N_A atoms of oxygen

= 0.11× N_A atoms of oxygen

Molar mass of water = 18g/mole

Thus, Number of moles of water =

1 mol of water (H₂O) contains = 1×N_A water molecules = 1 x N_A atoms of oxygen

Total number of oxygen atoms = Number of oxygen atoms from sucrose + Number of oxygen atoms from water

= 0.11 N_A + 1.0 N_A = 1.11N_A

Number of oxygen atoms in solution = 1.11 × Avogadro’s number

= 1.11 × 6.022 ×10²³

= 6.68 × 10²³

A change in the physical state can be brought about when energy is either given to or taken out from the system. Without any providing any energy to the system, there can be no physical change seen in the system.

Bismuth phosphate (BiPO₄) represents a correct chemical formula as in Bismuth phosphate (BiPO₄) both ions (Bi⁺³ and PO₄^-3) are trivalent.

* Note: The roman numerals written after the metal is the charge on that metal.
(a) The molecular formula of Copper(II)bromide = CuBr_2.

(b) The molecular formula of Aluminium (III) nitrate = Al(NO₃)₃

(c) The molecular formula of Calcium (II) phosphate = Ca₃(PO₄)₂

(d) The molecular formula of Iron (III) sulphide = Fe₂S₃

(e) The molecular formula of Mercury (II) chloride = HgCl₂

(f) The molecular formula of Magnesium (II) acetate = Mg(CH₃COO)₂

Molecular formulae of compounds are-

(i) CuCl₂

(ii) CuSO₄

(iii) Cu₃(PO₄)₂

(iv) NaCl

(v) Na₂SO₄

(vi) Na₃PO₄

(vii) FeCl₃

(viii) Fe₂(SO₄)₃

(ix) FePO₄

H₂ – It is a covalent compound.

(a) Chemical formula of compound formed from calcium and fluorine = CaF₂

(b) Chemical formula of compound formed from hydrogen and sulphur = H₂S

(c) Chemical formula of compound formed from nitrogen and hydrogen = NH₃ (d) Chemical formula of compound formed from carbon and chlorine = CCl₄ (e) Chemical formula of compound formed from Sodium and oxygen = Na₂O

(f) Chemical formula of compound formed from Carbon and oxygen = CO₂ or CO

(Aluminium fluoride a) Ammonia = NH₃

The atomic mass of N = 14

The atomic mass of H = 1

Thus, Ratio by mass = N : H × 3

= 14 : 1 × 3

= 14:3

(b) Carbon monoxide = CO

The atomic mass of C = 12

The atomic mass of O = 16

Thus, Ratio by mass = C:O

= 12:16

= 3:6

(c) Hydrogen chloride = HCl

The atomic mass of H = 1

The atomic mass of Cl = 35.5

Thus, Ratio by mass = H : Cl

= 1:35.5

(d) Aluminium fluoride = AlF₃

The atomic mass of Al = 27

The atomic mass of F = 19

Thus, Ratio by mass = Al : F × 3

= 27 : 19 × 3

= 27 : 57

= 9 : 19

(e) Magnesium sulphide = MgS

The atomic mass of Mg = 24

The atomic mass of S = 32

Thus, Ratio by mass = Mg : S

= 24 : 32

= 3 : 4

(a) The number of atoms in CO₃^2- = the atom of C + the atom of oxygen

= 1 + 3

= 4

(b) The number of atoms in PO₄^3– = the atom of P + the atoms of oxygen

= 1 + 4

= 5

(c) The number of atoms in P₂O₅ = the atoms of P + the atoms of oxygen

= 2 + 5

= 7

(d) The number of atoms in CO = the atom of C + the atoms of oxygen

= 1 + 1

= 2

The mass of 1 mole of a substance is equal to its relative atomic or molecular mass in grams.

Mass of one mole of neutrons = 1g

Mass of one neutron =

No of neutrons in H = 0

No of neutrons in O = 8

Total neutrons in water (H₂O) = 2 × 0 + 1 × 8 = 8

Mass of 8 neutrons =

The molar mass of water = 18g

Mass of one molecule of water =

Fraction of mass of water due to neutrons = = 0.444 = 44.44%

Yes, the solubility of a substance increase with an increase in temperature.

For example,

1. Take approximately 50 mL of water in a beaker.

2. Add sugar in the beaker with continuous stirring.

3. When no more sugar can be dissolved, heat the contents of the beaker. The temperature of the solution is brought to 40°C.

4. Start adding sugar again until it doesn’t dissolve in water anymore. The amount of sugar that has been added is calculated and recorded.

5. Steps 3 and 4 are again repeated at 60°C, 80°C, and 100°C and the results are recorded.

The results show that as the temperature of the water increases, the amount of salt dissolving in the solution is also higher.

The number of atoms constituting a molecule is known as its atomicity. On the basis of atomicity, the elements may be classified as follows:

(i) On heating the powder: sugar has a higher boiling point than salt. On heating, if the white powder is sugar, it will melt down to a light brown liquid form. Salt, on the other hand, will not melt.

(ii) Salt is a better conductor of electricity: The white powder is dissolved in water and conduction of electricity is checked. If the solution conducts electricity, it is a salt. This is because salt is made up of ions while sugar is made of uncharged particles.

The number of moles =
n =

Here, n = Number of moles

M = Given mass

M = Molar mass

Thus, the number of moles of magnesium (Mg) =

n = 0.5mole

(a) Mass of given sample = Number of moles X Molar mass

Thus, the mass of 5 moles of CO₂ = 5 × 44 (Molar mass of CO₂ = 44g/mole)

= 220g

The mass of 5 moles of H₂O = 5 × 18 (Molar mass of H₂O = 18g/mole)

= 90g

Therefore, we can say that 5 moles of CO₂ and 5 moles of H₂O do not have the same mass.

(b) Number of moles of given sample:

Thus, number of moles of 240 g of calcium:

n₁ =

n₁ = 6

Number of moles of 240 g magnesium:

n₂ =

n₂ = 10

Therefore, the ratio of number of moles: n₁ : n₂

6:10

3:5

Now, we can say that 240 g of calcium and 240 g magnesium elements have a mole ratio of 3:5.

(a) CaCO₃

Atomic mass of Ca = 40

Atomic mass of C = 12

Atomic mass of O = 16

Thus, CaCO₃ = 40 : 12 : 16 × 3

= 40 : 12 : 48

Ratio by mass = 10 : 3 : 12

(b) MgCl₂:

Atomic mass of Mg = 24

Atomic mass of Cl = 35.5

Thus, the ratio by mass = Mg : Cl x 2

= 24 : 35.5 x 2

= 24 : 71

(c) H₂SO₄:

Atomic mass of H = 1

Atomic mass of S = 32

Atomic mass of O = 16

Thus, the ratio by mass = 2XH : S : 4XO

= 2 : 32 : 64

= 1 : 16 : 32

(d) C₂H₅OH

The ratio by mass = 2XC : 6XH : O

= 2X12 : 6 : 16

= 24 : 6 : 16

= 12 : 3 : 8

(e) NH₃

The ratio by mass = N : 3 × H

14 : 1

(f) Ca(OH)₂

The ratio by mass = Ca : 2XO : 2 × H

= 40 : 32 : 2

= 20 : 16 : 1

Molar mass of CaCl₂ = The atomic mass of Ca + 2 × the atomic mass of Cl

= 40 + 35.5 × 2 = 111 g/mol

1 mole of calcium chloride = 111g

Thus, 222g of CaCl₂ is equivalent to 2 moles of CaCl₂

Since 1 formula unit CaCl₂ gives 3 ions (one Ca²⁺ cation and two Cl^- anions),

Therefore, 1 mole 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 ×10²³

= 36.132 ×10²³

= 3.6132 ×10²⁴ ions

A sodium atom and ion, differ by one electron. Sodium loses one electron to form sodium ion.

for 100 moles, each of sodium atoms and ions there would be a difference of 100 moles of electrons. Thus, the mass of 100 moles of electrons = 5.48002 g

As 1 mole of electron have 6.022 × 10²³ electrons

Therefore, mass of 6.022 × 10²³electrons =

Mass of one electron = = 9.1 ×10^-28 g

Molar mass of HgS = The molar mass of Hg + the molar mass of S

= 200.6 + 32 = 232.6 g mol^–1

1molecule of HgS contains 1 atom of Hg

232.6 g of HgS contains 200.6 g of Hg

Therefore, Mass of Hg in 225 g of HgS =

Mass of one steel screw = 4.11g

Mass of Earth = 5.98 × 10²⁴kg = 5.98 × 10²⁷kg

We know, 1 mole = 6.022 x 10²³

One mole of screws weigh = 4.11 x 6.022 x 10²³ = 2.48 ×10²⁴g

Mass of the Earth/ Mass of 1 mole of screws = 5.98 ×10²⁷ kg / 2.48 ×10²⁴ kg = 2.4 x 10³

Therefore, we can say that the mass of earth is 2.4×10³ times the mass of screws.

The earth is 2400 times heavier than one mole of the screw.

We know,

1 mole = 6.022 x 10²³

The number of moles =

n = 4.28mol

(a) The atomic mass of carbon atoms: 12

Thus, the mass of 5 moles of carbon atoms carried by Raunak:

m = Number of moles X Molar mass of given sample

= 5 × 12 = 60g

The atomic mass of sodium atoms:23

Thus, the mass of 5 moles of sodium atoms carried by Krish =

m = 5 ×23 = 115g

Thus, Krish’s container is heavier than Raunak’s container.

(b) The number of atoms = (Given mass)/(Molar mass)

(i) Raunak container (5 moles of carbon atoms):

Number of atoms =

(ii) Krish container (5 moles of sodium atoms):

Number of atoms =

Both containers have the same number of atoms.

(a) No of H₂O particles:

No of moles = 2

1 mole = 6.022 x 10²³

Thus, 2 moles of H₂O = 2 X 6.022 x 10²³ = 12.044 x 10²³ particles

(b) (i) No of moles of CO₂:

we know,

1 mole = 6.022 × 10²³

The number of moles

(ii) Thus, The number of moles =

Given mass = Number of moles x Molar mass

= 0.5 x 44

= 22g

(c) (i) The number of moles =

Molar mass of Na = 23g/mole

Given mass = 115g

Thus, the number of moles =

(ii) 1 mole = 6.022 x 10²³

Since, 5 moles = 5 x 6.022 X 10²³ = 30.11 X 10²³

(d) (i) No of moles of MgCl₂ = 0.5

The number of moles =

Molar mass of MgCl₂ = 95g/mole

Thus, mass of MgCl₂ = 0.5 X 95 = 47.5g

(ii) Number of particles: 1 mole = 6.022 x 10²³

0.5 mole = 0.5 x 6.022 x 10²³

Number of particles= 3.011 x 10²³

1 mole = 6.022 × 10²³

The number of moles

=

of stars are present in the visible universe.

10³ = 1000 = kilo

(b) 10^–1 = 1/10 = 0.1 = deci

(c) 10^–2 = 1/100 = 0.01 = centi

(d) 10^–6 = 0.000 001 = micro

(e) 10^–9 = 0.000 000 001 = nano

(f) 10^–12 = 0.000 000 000 001 = pico

(a) 5.84×10^-3 mg = 5.84×10^-9 kg

(b) 58.34 g = 5.834 x 10^-2 kg

(c) 0.584g = 5.84 x 10^-4 kg

(d) 5.873×10^-21g = (d) 5.873×10^-24 kg

A Mg atom and Mg²⁺ ion differ by two electrons.

For 10³ moles, each of magnesium atoms and ions there would be a difference of 10³ x 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

The number of atoms =

⇒ N = × N₀

The number of molecules in 100g of N₂:

Atomic mass of nitrogen (N) = 14

Molar mass of N₂ molecules = 14x2 = 28g

Number of atoms in N₂ = 1 + 1 = 2

= 2 X = 43.01X 10²³

The number of molecules in 100g of NH₃:

Molar mass of NH₃ molecules = 14+3X1 = 17g

number of atoms in NH₃ = 1 + 3 = 4

= 4 X

Therefore, NH₃ would have more atoms.

The molar mass of NaCl = The atomic weight of Na + The atomic weight of Cl

Atomic weight; Na = 22.99 g, Cl = 35.45 g

Thus, molar mass of NaCl = 23 + 35.5 = 58.5g/mole.

The number of moles =

Each NaCl particle contains one Na⁺ and one Cl^– ion = 2 ions

Total moles of ions = 0.1 × 2 = 0.2 moles

Number of ions = total number of moles of ions X Avogadro's number

Therefore,

No. of ions = 0.2 × 6.022 ×10²³

= 1.2042 ×10²³ ions

In the given sample, gold (Au) is 90%.

Thus, One gram of gold sample will contain =

The molar weight of gold = 197g/mole

The number of moles of gold (Au) =

We know, 1mole = 6.022 x 10²³

∴ 0.0046 mole of gold will contain = 0.0046 × 6.022 ×10²³

= 2.77 ×10²¹ atoms of gold particle

Ionic compounds: Ionic compounds are formed by the transfer of electrons are called as ionic compound. The bond found in these compounds are ionic in nature.

Positively charged ions are known as cations and negatively charged ions are known as anions. Ionic compounds are formed.

For example, sodium chloride (NaCl). Its constituent particles are positively charged sodium ions (Na⁺) and negatively charged chloride ions (Cl^–).

Molecular Compounds: They are also known as covalent compounds. Atoms of different elements join together in definite proportions to form molecular compounds. These compounds are formed by sharing of electrons between the two atoms and the elements are held together by covalent bonds.

These, are the pure substances, formed by non-metals. Molecular compounds can exist as either solid, liquid or gaseous state.

Examples: carbon dioxide, carbon monoxide, hydrogen chloride, water, methane etc.

Mass of 1 mole of aluminium atom = the molar mass of aluminium = 27 g mol^–1

A aluminium atom and ion, differ by three electrons. Aluminium loses three electrons to form aluminium ion.

The mass of one electron = 9.1×10^–28 g

For one mole of A1³⁺ ion, three moles of electrons are to be lost

Therefore, total number of electrons lost = 3

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 Al³⁺ = molar mass of aluminium – mass of electrons

= 27–0.00164 = 26.9984 g mol^–1

Therefore, difference in masses of one mole each of aluminium atoms and one mole of its ions

= 27 – 26.9984 = 0.0016 g

Mass of silver = ‘m’ g

Mass of gold = m/100 g

Number of atoms of silver(Ag) =

= {Atomic weight of Silver (Ag) = 108g/mole}

Number of atoms of gold(Au) =

=

Ratio of number of atoms of gold to silver = Au : Ag

= :

= 108 : 100 × 197

= 108 : 19700

= 1 : 182.41

Number of molecules of methane (CH₄) = 1.5 ×10²⁰

Mass of 1 mole of CH₄ = 16 g

Mass of 1 mole of ethane (C₂H₆) = 30g

1 mole of substances contains 6.022 X 10²³ molecules.

Thus, the mass of 6.022 X 10²³ molecules of CH₄ = 16 g

Thus, the mass of 1.5 ×10²⁰ molecules of methane = 1.5 ×10²⁰ × 16/ 6.022 X 10²³

= 3.98 x 10^-3g

Mass of molecules of C₂H₆ is = Mass of CH₄(given)

Mass of 6.022 X 10²³ molecules of C₂H₆ = 30g

Therefore, 3.98 x 10^-3g of ethane will contain = 6.022 x 10²³ x 3.98 x 10^-3 / 30

= 0.8 × 10²⁰ molecules

(a) In a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is called law of conservation of mass.

(b) A group of atoms carrying a fixed charge on them is called polyatomic ion.

(c) The formula unit mass of Ca₃ (PO₄)₂ is (3 × atomic mass of Ca) + (2 × atomic mass of phosphorus) + (8 × atomic mass of oxygen) = 310

(d) Formula of sodium carbonate is Na₂CO₃ and that of ammonium sulphate is (NH₄)₂SO_4.

The names of these elements are given as follows:

The total number of inert gases in this puzzle is six. Their names and symbols are as follows:

(a) The chemical formula of caustic potash is KOH.

Molecular mass of Caustic potash (KOH) = The molar mass of K + the molar mass of O + molar mass of H

= 39 + 16 + 1 = 56g/mole

(b) The chemical formula of baking powder is NaHCO_3.

Molecular mass of baking powder (NaHCO₃) = 23 + 1 + 12 + 3 X 16

= 84g/mole

(c) The chemical formula of Lime stone is CaCO₃.

= 40 + 12 + 3X16

= 100g/mole

(d) The chemical formula of Caustic soda is NaOH.

Molecular mass of Caustic soda (NaOH) = 23+ 16+1

= 40g/mole

(e) The chemical formula of Ethanol is C₂H₅OH.

Molecular mass of Ethanol (C₂H₅OH) = 2 X 12 + 5 X 1 + 16 + 1

= 46g/mole

(f) The chemical formula of Common salt is NaCl.

Molecular mass of Common salt (NaCl) = 23 + 35.5 = 58.5g/mole

During photosynthesis, following reaction takes place:

6 CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

1 mole glucose needs 6 moles of water.

Molar mass of glucose (C₆ H₁₂ O₆) = 180g

molar mass of water = 18g

We know, Number of moles =

180 g of glucose needs = (6 x 18)g of water

1g glucose will need =

18g glucose would need =

Volume =

The density of water = 1 gcm^-3

Therefore, volume of water consumed = =