Determine the molecular formula of an oxide of iron in which the mass per cent of iron and oxygen are 69.9 and 30.1 respectively. Given that the molar mass of the oxide is 159.69 g mol–1.
From the available data Percentage of iron = 69.9
Percentage of oxygen= 30.1
Total percentage of iron & oxygen= 69.9+30.1= 100%
Step 1 calculation of simplest whole number ratios of the elements
Element |
Percentage |
Atomic mass |
Atomic ratio |
Simplest ratio |
Simplest whole no ratio |
Fe |
69.9 |
55.84 |
69.9/55.84=1.25 |
1.25= 1 |
2 |
O |
30.1 |
16 |
30.1/16 = 1.88 |
1.88=1.5 |
3 |
Step 2 Writing the empirical formula of the compound
The empirical formula of the compound = Fe2 O3
Step 3 determination of molecular formula of the compound
Empirical formula mass = 2 X69.9 + 3 X16=187.8 amu
Molecular mass of oxide= 159.69g/mol(given)
Now we know molecular formula = n x Empirical formula
And n= molecular mass / empirical formula mass= 159.69/187.8 = 0.85 = approx 1
Therefore molecular formula = n x empirical formula
=1 x(Fe2O3) = Fe2O3
The molecular formula of the oxide is Fe2O3
Calculate the amount of carbon dioxide that could be produced when
(i) 1 mole of carbon is burnt in air.
(ii) 1 mole of carbon is burnt in 16 g of dioxygen.
(iii) 2 moles of carbon are burnt in 16 g of dioxygen.
In a reaction A + B2 → AB2 Identify the limiting reagent, if any, in the following reaction mixtures.
(i) 300 atoms of A + 200 molecules of B
(ii) 2 mol A + 3 mol B
(iii) 100 atoms of A + 100 molecules of B
(iv) 5 mol A + 2.5 mol B
(v) 2.5 mol A + 5 mol B
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(i) 1 g Au (s)
(ii) 1 g Na (s)
(iii) 1 g Li (s)
(iv) 1 g of Cl2(g)
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4HCl(aq) + MnO2(s) → 2H2O(l) + MnCl2(aq) + Cl2(g)
How many grams of HCl react with 5.0 g of manganese dioxide?
Determine the empirical formula of an oxide of iron which has 69.9% iron and 30.1% dioxygen by mass.
A sample of drinking water was found to be severely contaminated with chloroform, CHCl3, supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass).
(i) Express this in percent by mass.
(ii) Determine the molality of chloroform in the water sample.
Calcium carbonate reacts with aqueous HCl to give CaCl2 and CO2 according to the reaction,
CaCO3(s) + 2 HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)
What mass of CaCO3 is required to react completely with 25 mL of 0.75 M HCl?
Calculate the mass of sodium acetate (CH3COONa) required to make 500 mL of 0.375 molar aqueous solution. Molar mass of sodium acetate is 82.0245 g mol–1
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(i) empirical formula,
(ii) molar mass of the gas, and
(iii) molecular formula.
How many significant figures are present in the following?
(i) 0.0025
(ii) 208
(iii) 5005
(iv) 126,000
(v) 500.0
(vi) 2.0034
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What are hybridisation states of each carbon atom in the following compounds ?
(i) CH2=C=O,
(ii) CH3CH=CH2,
(iii) (CH3)2CO,
(iv) CH2=CHCN,
(v) C6H6
What will be the minimum pressure required to compress 500 dm3 of air at 1 bar to 200 dm3 at 30°C?
What are the common physical and chemical features of alkali metals?
Assign oxidation number to the underlined elements in each of the following species:
(a) NaH2PO4
(b) NaHSO4
(c) H4P2O7
(d) K2MnO4
(e) CaO2
(f) NaBH4
(g) H2S2O7
(h) KAl(SO4)2.12 H2O
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Explain the formation of a chemical bond.
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(i) used to determine heat changes
(ii) whose value is independent of path
(iii) used to determine pressure volume work
(iv) whose value depends on temperature only.
A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.
a) What is the initial effect of the change on vapour pressure?
b) How do rates of evaporation and condensation change initially?
c) What happens when equilibrium is restored finally and what will be the final vapour pressure?
Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.
Give the IUPAC names of the following compounds:
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(b) F > O > Cl > N
(c) Cl > F > O > N
(d) O > F > N > Cl
Explain structures of diborane and boric acid.
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(a) Na (b) K (c) Rb (d) Cs
Draw the structure of (i) BeCl2 (vapour) (ii) BeCl2 (solid).
Compare the solubility and thermal stability of the following compounds of the alkali metals with those of the alkaline earth metals.
(a) Nitrates (b) Carbonates (c) Sulphates.
Discuss the pattern of variation in the oxidation states of
(i) B to Tl and (ii) C to Pb.
Find out the value of Kc for each of the following equilibria from the value of Kp:
(i) 2NOCl (g) ↔ 2NO (g) + Cl2 (g); Kp = 1.8 × 10–2 at 500 K
(ii) CaCO3 (s) ↔ CaO(s) + CO2(g); Kp = 167 at 1073 K
Define octet rule. Write its significance and limitations.
What are the various factors due to which the ionization enthalpy of the main group elements tends to decrease down a group?
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Respected teacher, You have taken the percentage of iron instead of the molar mass of iron while calculating the Empirical Formula mass.Thank you for making available such detailed answers to us.
In NCERT the molecular mass of oxide is not given....that's why I was in trouble to find the answer...thank's for this information..