Chemistry Questions & Answers

Question \( 5 \quad \) [26 marks] \( \begin{array}{l}\text { Substance } A \text { has a molecular formula of } \mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}_{2} \text {. Substance } \mathrm{A} \text { has the smell of apples. It is a } \\ \text { product of the reaction between butanoic acid and an alcohol } B \text {. } \\ \text { Answer the following questions based on the above statement: } \\ \text { 5.1.1 What family of organic compounds does substance } A \text { belong to? } \\ \text { 5.1.2 Draw the expanded structure of compound } A \text {. }\end{array} \) (1)

The water dissolves some of the chemicals in the tea leaves when you are using a tea bag to make tea.

4.4 Boric acid, \( \mathrm{B}(\mathrm{OH})_{3} \), a weak acid is used as a mild antiseptic. It ionizes in water as follows: \[ \mathrm{B}(\mathrm{OH})_{3}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightleftharpoons \mathrm{B}(\mathrm{OH})_{4}^{-}(\mathrm{aq})+\mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq}) \] 4.4.1 Calculate the hydronium ion concentration of a 0.015 M aqueous solution of boric acid, given that the equilibrium constant for this reaction is \( 5.9 \times 10^{-10} \).

Question \( 4 \quad[20 \) marks \( ] \) \( 4.1 \quad \) Write an equation in which \( \mathrm{H}_{2} \mathrm{PO}_{3}^{-} \)acts as an acid and another in which it acts as a base. (2) 4.2 A shampoo solution at \( 25^{\circ} \mathrm{C} \) has a hydroxide ion concentration of \( 1.5 \times 10^{-9} \mathrm{M} \). 4.2 .1 Calculate its hydronium ion concentration. 4.2 .2 Is this solution acidic, neutral, or basic? Give a reason for your answer. 4.3 A 1.00 L aqueous solution contained 5.80 g of sodium hydroxide, \( \mathrm{NaOH} . \mathrm{Calculate} \) the pH of this solution at \( 25^{\circ} \mathrm{C} \) ?

Alcoholes \( \begin{array}{l}\text { a) 2-propanol } \\ \text { b) 2-metil-2-butanol } \\ \text { c) 3-hexanol }\end{array} \)

3.2 Propane, \( \mathrm{C}_{3} \mathrm{H}_{8} \), is a common fuel gas. Use the following information to calculate the mass of propane you would need in order to provide 369 kJ of heat. \[ \mathrm{C}_{3} \mathrm{H}_{8}(\mathrm{~g})+5 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow 3 \mathrm{CO}_{2}(\mathrm{~g})+4 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \quad \Delta \mathrm{H}=-2043 \mathrm{~kJ} \]

10. Señala cuáles de los siguientes procesos son cambios físicos y cuáles cambios químicos a) Vaporización del agua. b) Mezcla en un recipiente de dos gases, o hidrógeno.

\( HNO _ { 3 } + Ca ( OH ) _ { 2 } \rightarrow Ca ( NO _ { 3 } ) _ { 2 } + H _ { 2 } O \)

A sample of diborane gas \( \left(\mathrm{B}_{2} \mathrm{H}_{6}\right) \), a substance that bursts into flames when exposed to air, has a pressure of 345 torr at a temperature of \( -15^{\circ} \mathrm{C} \) and a volume of 3.48 L . If conditions are changed so that the temperature is \( 36{ }^{\circ} \mathrm{C} \) and the pressure is 468 torr, what will be the volume of the sample?

9. Indica cuál de los sigulentes procedimlentos el más adecuado para separar una mezcla de sal, azufre y gasolina. Justifica tu elección explica por qué rechazas cada uno de los otros a) Calentar para que la gasolina se evapore y separar después la sal y el azufre añadiendo agua. Al filtrar quedaría el azufre en el papel y separaría la sal del agua por evaporación del agua. b) Filtrar para separar la gasolina de los sólidos. Añadir agua sobre el mismo filtro para que se dlsuelva la sal y separarla del azufre por filtración. Recuperarla dejando evaporar el agua d) Calentar para que primero se evapore la gasolina y después se funda el azufre.