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By means of chemical equations express the following chemical reactions:
(a) [Cr(H2O)6]Cl3 dissolved in water, is mixed with an excess of sodium hydroxide solution. A clear green solution is formed. The colour of the solution changes to yellow when an aqueous hydrogen peroxide solution is added.
(b) If an aqueous solution of a violet manganese compound is mixed with a hydrogen peroxide solution, the resulting solution is decolourised and a gas is released from it.
(a) [Cr(H2O)6]3+ 4OH–→ [Cr(OH)4(H2O)2]– + 4H2O 2[Cr(OH)4(H2O)2]– + 3H2O2 + 2OH– → 2 CrO2-4+12H2O (b) Equation is given in 2a.
(a) [Cr(H2O)6]3+ 4OH–→ [Cr(OH)4(H2O)2]– + 4H2O
2[Cr(OH)4(H2O)2]– + 3H2O2 + 2OH– → 2 CrO2-4+12H2O
(b) Equation is given in 2a.
See lessAn amount of 20 g of cooper (II) oxide was treated with a stoichiometric amount of a warm 20% sulphuric acid solution to produce a solution of copper (II) sulphate.
How many grams of crystalline copper(II) sulphate (CuSO4 . 5 H2O) have crystallised when the solution is cooled to 20 °C?
Relative atomic masses: Ar(Cu) = 63.5; Ar(S) = 32; Ar(O) = 16; Ar(H) = 1
Solubility of CuSO4 at 20 oC: s = 20.9 g of CuSO4 in 100 g of H2O.
CuO + H2SO4 → CuSO4 + H2O n(CuO) = m(CuO)/M(CuO) = 20 g/79.5 g mol-1 = 0.2516 gn(H2SO4) = n(CuSO4) = 0.2516 mol Mass of the CuSO4 solution obtained by the reaction: m(solution CuSO4) = m(CuO) + m(solution H2SO4) = = m(CuO) + n(H2SO4) x M(H2SO4)/w(H2SO4) = 20 g + 0.2516 mol 98 g mo-1/ 0.20m(solutionRead more
CuO + H2SO4 → CuSO4 + H2O
n(CuO) = m(CuO)/M(CuO) = 20 g/79.5 g mol-1 = 0.2516 g
n(H2SO4) = n(CuSO4) = 0.2516 mol
Mass of the CuSO4 solution obtained by the reaction:
m(solution CuSO4) = m(CuO) + m(solution H2SO4) =
= m(CuO) + n(H2SO4) x M(H2SO4)/w(H2SO4)
= 20 g + 0.2516 mol 98 g mo-1/ 0.20
m(solution CuSO4) = 143.28 g
Mass fraction of CuSO4:
(a) in the solution obtained:
w(CuSO4) = m(CuSO4)/m(solution CuSO4)
= n(CuSO ) (CuSO )/(solution CuSO4) = 028
(b) in saturated solution of CuSO4 at 20°C:
w(CuSO4) = 209 g/120.9 g = 0.173
(c) in crystalline CuSO4 . 5 H2O:
w(CuSO4) = M(CuSO4)/M (CuSO4.5H2O) =0.639
Mass balance equation for CuSO4:
0.28 m = 0.639 m1 + 0.173 m2
m – mass of the CuSO4 solution obtained by the reaction at a higher temperature.
m1 – mass of the crystalline CuSO4 .5H2O.
m2 – mass of the saturated solution of CuSO4 at 20 °C.
0.28 × 143.28 = 0.639 m1 + 0.173 × (143.28 – m1)
m1 = 32.9 g
The yield of the crystallisation is 32.9 g of CuSO4 . 5H2O.
See lessWhich of the following acid-base pairs is most suitable for keeping the pH constant at 9 in an aqueous solution?
(a) CH3COOH – CH3COO–
(b) NH+4 – NH3
(c) H2CO3 –HCO–3
(d) H2PO–4 –HPO2-4
(e) H2C2O4 – HC2O–4
(b) NH+4 – NH3
(b) NH+4 – NH3
See lessOne of the following statements cannot be correct. State which one.
(a) A water-soluble solid contains Mg2+, Cr3+, and Br– .
(b) A solid soluble in a sodium hydroxide solution contains Al3+, K+, and SO2-4.
(c) A solid soluble in aqueous ammonia solution contains Ag+, Cu2+, and Cl– .
(d) A solid soluble in nitric acid contains Ba2+, Fe2+, and CO2-3 .
(e) A solution neutral to litmus contains Na+, Ca2+, and PO3-4 .
(e) A solution neutral to litmus contains Na+, Ca2+, and PO3-4 .
(e) A solution neutral to litmus contains Na+, Ca2+, and PO3-4 .
See lessExplain by means of generally used international symbols and formulas which compounds are named as peroxo compounds. Write summary formulas for six of them.
Peroxo compounds contain the functional group: O2-2Examples: H2O2, Na2O2, BaO2, H2SO5, H2S2O8, K2C2O6, CrO5, [VO2]3+
Peroxo compounds contain the functional group: O2-2
Examples: H2O2, Na2O2, BaO2, H2SO5, H2S2O8, K2C2O6, CrO5, [VO2]3+
See lessComplete the following equation: H3AsO4 + Zn → AsH3 + Zn2+
The reaction is carried out in an acid solution. Fill in the missing particles and balance the reaction equation.
H3AsO4 + 4Zn + 8H+ → AsH3 + 4Zn2+ + 4H2O
H3AsO4 + 4Zn + 8H+ → AsH3 + 4Zn2+ + 4H2O
See lessA compound A contains 38.67 % of potassium, 13.85 % of nitrogen, and 47.48 % of oxygen. On heating, it is converted to a compound B containing 45.85 % of potassium, 16.47 % of nitrogen, and 37.66 % of oxygen.
Problem:
What are the stoichiometric formulas of the compounds?
Write the corresponding chemical equation.
Compound A: KxNyOz x : y : z = 38.67/39.1 = 13.85/14 = 47.48/16 = 0.989 : 0.989 : 2.968 = 1 : 1 : 3 A : KNO3 Compound B: KpNqOrp : q r: 45.67/39.1 = 16.47/14 = 37.66/16 = 1.173 : 1.176 : 2.354 = 1 : 1 : 2 B : KNO2 Equation: 2 KNO3 → 2 KNO2 + O2
Compound A:
KxNyOz
x : y : z = 38.67/39.1 = 13.85/14 = 47.48/16 = 0.989 : 0.989 : 2.968 = 1 : 1 : 3
A : KNO3
Compound B:
KpNqOr
p : q r: 45.67/39.1 = 16.47/14 = 37.66/16 = 1.173 : 1.176 : 2.354 = 1 : 1 : 2
B : KNO2
Equation: 2 KNO3 → 2 KNO2 + O2
See lessThe IUPAC name of the compound is:
(a) 5-bromo-1-hexanoic acid
(b) 5-bromo-2-hydroxy-1-hexanal
(c) 2-bromo-5-hydroxy-6-hexanal
(d) 2-bromo-2-hydroxy-1-hexanal
(e) 5-bromo-2-hydroxy-1-hexanone
(b) 5-bromo-2-hydroxy-1-hexanal
(b) 5-bromo-2-hydroxy-1-hexanal
See lessQuantitative analysis for carbon and hydrogen was originally carried out using a technique and apparatus (see figure) originally developed in 1831 by the famous chemist Justus Liebig. A carefully weighed sample of organic compound (C) is placed in a combustion tube (A) and vaporized by heating in a furnace (B). The vapours are swept by a stream of oxygen through a heated copper oxide packing (D) and through another furnace (E), which ensures the quantitative oxidation of carbon and hydrogen to carbon dioxide and water. The water vapour is absorbed in a weighed tube (F) containing magnesium perchlorate and the carbon dioxide in another weighed tube (G) containing asbestos impregnated with sodium hydroxide.
A pure liquid sample containing only carbon, hydrogen and oxygen is placed in a 0.57148 g platinum boat, which on reweighing weights 0.61227 g.The sample is ignited and the previously weighed absorption tubes are reweighed.The mass of the water absorption tube has increased from 6.47002 g to 6.50359 g, and the mass of the carbon dioxide tube has increased from 5.46311 g to 5.54466 g.
(a) Calculate the mass composition of the compound.
(b) Give the empirical formula of the compound.To estimate the molar mass of the compound,1.0045 g was gasified. The volume, measured at a temperature of 350 K and a pressure of 35.0 kPa, was 0.95 dm3.
(c) Give the molar mass and the molecular formula of the compound.
(d) Draw possible structures corresponding to the molecular formula excluding cyclic structures, stereo isomers, peroxides and unsaturated compounds.There are about 15 possibilities.Give 10 of them.
When the compound is heated with a sodium hydroxide solution, two products are formed. Fractional distillation of the reaction mixture yields one of the substances.The other substance is purified by distillation after acidification and appears to be an acid.
(e) What structures are possible for compound C?
0.1005 g of the acid are dissolved in water and titrated with a sodium hydroxide solution with a concentration of 0.1000 mol dm-3. The indicator changes colour on addition of 16.75 cm3 of hydroxide solution.
(f) What was the original substance C?
(a) Mass percentage composition: 54.56 % C; 9.21 % H; 36.23 % O (b) Empirical formula: C2H4O (c) Molar mass: 88 g mol-1 Molecular formula: C4H8O2 (d) Possible structures: 1. CH3-CH2-CH2-COOH 2. CH3-CH(CH3)-COOH 3. CH3-O-CO-CH2-CH3 4. CH3-CH2-O-CO-CH3 5. CH3-CH2-CH2-O-CO-H6. CH3-CH(CH3)-O-CO-H 7. CHRead more
(a) Mass percentage composition: 54.56 % C; 9.21 % H; 36.23 % O
(b) Empirical formula: C2H4O
(c) Molar mass: 88 g mol-1 Molecular formula: C4H8O2
(d) Possible structures:
1. CH3-CH2-CH2-COOH
2. CH3-CH(CH3)-COOH
3. CH3-O-CO-CH2-CH3
4. CH3-CH2-O-CO-CH3
5. CH3-CH2-CH2-O-CO-H
6. CH3-CH(CH3)-O-CO-H
7. CH3-CH2-CH(OH)-CHO
8. CH3-CH(OH)-CH2-CHO
9. CH2(OH)-CH2-CH2-CHO
10. CH3-C(OH)(CH3)-CHO
11. CH2(OH)-CH(CH3)-CHO
12. CH3-O-CH2-CH2-CHO
13. CH3-CH2-O-CH2-CHO
14. CH3-O-CH(CH3)-CHO
15. CH3-CH2-CO-CH2-OH
16. CH3-CH(OH)-CO-CH3
17. CH2(OH)-CH2-CO-CH3
18. CH3-O-CH2-CO-CH3
(e) The possible structures are 3, 4, 5, 6.
(f) The structure of the compound C is CH3-CH2-O-CO-CH3.
See lessWrite down equations for the reactions:
Oxidation of chromium(III) chloride with bromine in alkaline solution (KOH).
2CrCl3 + 3 Br2 + 16 KOH → 2 K2CrO4 + 6 KBr + 6 KCl + 8 H2O
2CrCl3 + 3 Br2 + 16 KOH → 2 K2CrO4 + 6 KBr + 6 KCl + 8 H2O
See less