5. Referente Teórico
5.1 Enseñanza de las ciencias
1. A = Z + N
where A = nucleon number, Z = proton number and N = number of neutrons.
2. From the mass spectrum of an element which has n isotopes with m/e ratios of m1, m2, ..., mn:
Relative atomic mass = ∑(miQi)
∑Qi =
m1Q1 + m2Q2 + … + mnQn Q1 + Q2 + … + Qn
where mi = m/e ratio, Qi = relative height of peak or relative abundance 3. Avogadro constant = 6.02 × 1023 mol–1
4. Amount of substance (mol) = Number of atoms or molecules Avogadro constant 5. Mass = Number of moles ×Ar (or Mr)
6. Concentration (mol dm–3) = Amount of solute (mol) Volume of solution (dm3)
7. Concentration (g dm–3) = Concentration (mol dm–3) × Relative molecular mass
Chapter-01.indd 39
8. Amount of solute (mol) = Concentration (mol dm
–3) × Volume (cm3) 1000
9. Molality = Moles of solute Mass of solvent (kg) nA = number of moles of A, 10. Mole fraction of A (XA) = nA nA + nB where nB = number of moles of B
11. Percentage by mass (% w/w) = Mass of component
Total mass of solution × 100%
12. Percentage by volume (% v/v) = Volume of component
Total volume of solution× 100%
13. Percentage yield = Actual yield
Theoretical yield× 100%
14. One mole of any gas occupies a volume of 22.4 dm3 at s.t.p. (0 °C, 1 atm) and 24 dm3 at room temperature and pressure.
Focus on Exam
1
OBJECTIVE QUESTIONS
1. Which of the following atoms contain twelve neutrons?
A 199F and 2412Mg B 199F and 2010Ne C Mg and 2311Na D 199F and 2311Na
2. Which of the following species has (a) more protons than electrons, (b) more protons than neutrons? (H = 1 1H; D = 2 1H; O = 16 8O) A D2O B D3O+ C H 3O + D HO– 3. Which statement is true of the two isotopes,
12 6C and
14 6C?
A They have the same number of neutrons. B They have the same relative isotopic mass. C They have a different number of electrons. D They have different physical properties. 4. A sample of nitrogen gas contains the 14N and
15N isotopes. How many lines corresponding to the N2+ species are found in the mass spectrum of nitrogen gas?
A 2 C 4
B 3 D 5
5. The mass spectrum of neon is shown in the following figure. The relative atomic mass of neon is 20.18.
What are the values of x and y? x y A 0.1 9.0 B 0.2 8.9 C 0.4 8.4 D 0.5 8.6
6. When 69.0 g of lead were heated in excess oxygen, 79.6 g of an oxide of lead were obtained. What is the empirical formula of the oxide?
(Relative atomic mass: O, 16; Pb, 207) A PbO C Pb2O3 B PbO2 D Pb3O4
7. The equation for the reaction of chromium(III)
oxide with carbon monoxide is shown below. Cr2O3 + 3CO → 2Cr + 3CO2
What is the mass of chromium produced when 5.46 kg of chromium(III) oxide reacts with excess
carbon monoxide?
(Relative atomic mass: O, 16.0; Cr, 52.0)
relative abundance 20 21 22 10Ne (90.9%) m/e 20 10Ne (y %) 22 10Ne (x %) 21 Chapter-01.indd 40 Chapter-01.indd 40 4/30/2012 7:11:38 PM4/30/2012 7:11:38 PM
A 0.933 kg C 1.86 kg B 1.243 kg D 3.73 kg
8. What is the volume of oxygen gas at s.t.p. which contains 1.5 × 1024 oxygen atoms?
(Molar volume of gas = 22.4 dm3 at s.t.p.; Avogadro constant = 6.02 × 1023)
A 14 dm3 C 56 dm3 B 28 dm3 D 70 dm3
9. 0.24 g of a sample of a monobasic acid requires 8.0 cm3 of sodium hydroxide solution for a complete reaction. If the concentration of the sodium hydroxide solution is 0.4 mol dm–3, what is the relative molecular mass of the acid?
A 37.5 C 75
B 62.5 D 125
10. Hydroxylamine (NH2OH) and its salts are powerful reducing agents. The half-equations for the reaction between hydroxylamine and bromate(V) ions are shown below.
NH2OH(aq) ➝ NO(g) + 3H+(aq) + 3e– BrO3–(aq) + 6H+(aq) + 6e– ➝ Br–(aq) + 3H
2O What is the volume of 0.25 mol dm–3
hydroxylamine required to react completely with 25.0 cm3 of 0.2 mol dm–3 potassium bromate(
V)
solution?
A 20.0 cm3 C 30.0 cm3 B 25.0 cm3 D 40.0 cm3
11. When excess silver nitrate solution was added to 25.0 cm3 of magnesium chloride solution, 2.87 g of silver chloride were precipitated. What is the concentration of magnesium chloride?
(Relative atomic masses: Ag, 108; Cl, 35.5) A 0.1 mol dm–3 C 0.4 mol dm–3 B 0.2 mol dm–3 D 0.8 mol dm–3
12. What is the mole fraction of hydrogen chloride in hydrochloric acid which contains 36% HCl by mass?
A 0.11 C 0.33 B 0.22 D 0.44
13. What are the changes in the oxidation numbers of iodine and sulphur for the following reaction? KIO3 + 2Na2SO3➝ KIO+ 2Na2SO4
Iodine Sulphur
A +5 to +1 +4 to +6
B +5 to +1 +2 to +4
C +1 to –1 +4 to +6
D –1 to +1 +2 to +4
For questions 14 to 18, use this table to select the correct answer. A B C D I only is correct I and II only are correct II and III only are correct I, II and III are correct
14. The mass spectrum of an element shows I the relative isotopic mass of the isotopes
of the element
II the relative abundances of isotopes III the average atomic mass of the element 15. Which of the following chlorine compounds
contain the same number of atoms as the number of atoms in two moles of chlorine gas?
I 2 mol hydrogen chloride II 1 mol chlorous acid, HClO2 III 2 mol chlorine monoxide, Cl2O
16. Which of the following statements is/are correct?
I The mass of one atom of aluminium is 27
6.02 × 1023 g.
II One mole of oxygen molecules contains 6.02 × 1023 oxygen atoms.
III One mole of aluminium has the same mass as one mole of oxygen molecules.
(Relative atomic mass: O, 16; Al, 27; Avogadro constant = 6.02 × 1023)
17. The combustion of heptane (C7H16) in excess oxygen can be represented by the following chemical equation:
C7H16 + 11O2➝ 7CO2 + 8H2O
The combustion of 25.0 g of heptane in excess oxygen will produce
I 36 g of water
II 42 dm3 of carbon dioxide at room temperature III 7 moles of carbon dioxide
(Relative atomic mass: H, 1; C, 12; O, 16; 1 mole of any gas occupies 24.0 dm3 at room temperature.)
18. A solution is made by dissolving 5.0 g of toluene (C7H8) in 225 g of benzene (C6H6). Which of the following statements is/are correct?
I The solution contains 0.054 mole of toluene.
II The molality of the solution is 0.24 mol kg–1. III The molarity of the solution is 0.30 M.
Chapter-01.indd 41
SUBJECTIVE QUESTIONS
1. (a) X+ and Y2– ions and the isotope 40
18Z have the same number of electrons. With reference to the periodic table, identify X+ and Y2–. (b) Complete the table to show the numbers
of protons, neutrons and electrons for the following species. Species Number of protons Number of neutrons Number of electrons 60 28Ni 31P3– 16 Fe2+ 30 24
2. (a) Germanium is used in the manufacture of semiconductor devices. Give the relative mass and charge for the three types of particles present in germanium atoms. (b) Analysis using mass spectrometer shows that
boron consists of two isotopes, 10B and 11B. Calculate the percentage relative abundance for each isotope, given that the ratio of relative abundance for the two isotopes is:
10B
–— = 0.23
11B
3. The mass spectrum of an element X is shown below. relativ e ab undance 90.9% 0.26% 20 21 22 m/e 8.8%
Calculate the relative atomic mass of X. 4. (a) Define the term mole.
(b) Calculate
(i) the number of particles in 0.02 mole of water molecules,
(ii) the number of moles in 3.01 × 1022 copper atoms,
(iii) the mass of 0.75 mole of urea, CO(NH2)2.
(Relative atomic mass: H, 1; C, 12; N, 14; O, 16; Avogadro constant = 6.02 × 1023)
5. (a) Naturally occurring carbon has two isotopes: 12C and 13C. The relative atomic mass of carbon is 12.01 a.m.u. If the relative isotopic mass of 12C = 12.00 a.m.u. and 13C = 13.00 a.m.u., what is the relative abundance of the 13C isotope?
(b) 37.3 g of CuSO4.5H2O is dissolved in 0.40 L of solution. Calculate the molarity of the solution.
(c) How much water should be added to 350 cm3 of 4.0 mol dm–3 sodium hydroxide solution so that the final molarity of the solution is 2.5 mol dm–3?
6. (a) Outline how you would prepare 250 cm3 of 2.0 mol dm–3 sodium carbonate solution. (b) A 250 mL sodium hydroxide solution is
prepared by dissolving 1.0 g of sodium hydroxide in water. 25 mL of the solution is neutralised by sulphuric acid, H2SO4(aq). Calculate the number of moles of H2SO4
used.
(Relative atomic mass: H, 1; O, 16; Na, 23) 7. When 6.08 g of metal oxide, M2O3 are reacted
with excess hydrogen, metal M and 2.16 g of water are formed.
M2O3(s) + 3H2(g) ➝ 2M(s) + 3H2O Calculate the relative molecular mass of M2O3
and the relative atomic mass of M. (Relative atomic mass: H, 1; O, 16)
8. (a) An organic compound contains carbon, hydrogen and oxygen only. 1.84 g of the organic compound give 3.52 g of carbon dioxide and 2.16 g of water on complete combustion. Determine the empirical formula of the organic compound.
(Relative atomic mass: H, 1; C, 12; O, 16) (b) A hydrocarbon, CxHy, is burnt in excess
oxygen. If 112 cm3 of hydrocarbon at s.t.p. produce 0.88 g of carbon dioxide, what is the value of x in the molecular formula of the hydrocarbon?
9. 1.52 g of an iron compound consisting of iron and chlorine only were dissolved completely in water. Excess silver nitrate solution was added to the metal chloride solution. The mass of silver chloride produced was 4.02 g. Calculate the empirical formula of the metal chloride.
(Relative atomic mass: Fe, 56; Ag, 108; Cl, 35.5)
Chapter-01.indd 42
10. (a) What is the meaning of limiting reagent? (b) Balance the following equation: MO2 + HCl → MCl2 + Cl2 + H2O (c) 1.5 g of MO2 were added to 40 cm3 of 2.0
mol dm–3 hydrochloric acid.
(i) Determine the limiting reagent in the reaction.
(ii) Calculate the volume of chlorine produced at room conditions.
(Relative molecular mass of MO2 = 87.2; molar volume = 24.0 dm3 at room conditions)
11. Concentrated sulphuric acid has a density of 1.84 g cm–3 and contains 98% (by mass) of H2SO4.
(a) Calculate the molarity of concentrated sulphuric acid.
(b) What volume of concentrated sulphuric acid is needed to prepare 1.0 L of 0.5 M H2SO4?
(c) Calculate the concentration (g dm–3) of 0.5 M sulphuric acid.
(Relative atomic mass: H, 1; S, 32; O, 16) 12. (a) 1.40 g of iron is dissolved in excess dilute
sulphuric acid. What is the volume (at s.t.p.) of hydrogen produced in this reaction? (Relative atomic mass: Fe, 55.8)
(b) Solution X containing 0.020 mol of iron(II)
sulphate requires 22.5 cm3 of potassium manganate(VII) for complete reaction. The
equation for the reaction is: 5Fe2+ + MnO
4
– + 8H+➝ Mn2+ + 4H 2O +
5Fe3+
What is the molarity of the KMnO4 solution? (c) When ethanoic acid, CH3COOH, reacts
with calcium hydroxide, salt and water are produced. Determine the maximum mass of the salt obtained if 27.6 g of calcium hydroxide are used for the reaction. (Relative atomic mass: H, 1; C, 12; O, 16;
Ca, 40.1)
Chapter-01.indd 43