(a) (i) Define a base according to Arrhenius concept.
(ii) Give one example of an Arrhenius base.
(iii) Identify each of the following substances in aqueous solutions as strong electrolyte, non-electrolyte or weak electrolyte.
I. C\(_{12}\)H\(_{22}\)O\(_{11}\) II. NH\(_3\) Ill. NaOH
(iv) Write a balanced equation to represent the reaction between CH\(_3\)COOH and KOH.
(b) Calculate the volume of 0.500 mol dm\(^{-3}\) HCI required to neutralize 20.00 cm\(^3\) of 0.300 mol dm\(^{-3}\) NaOH.
(c) Give the IUPAC name of each of the following salts: (ii) NaOCI; (iii) Mg(HCO\(_3\))\(_2\).
(d)(i) Define the term standard solution.
(ii) Consider the following compounds: NaOH and Na\(_2\)CO\(_3\). Which of the compounds is suitable for the preparation of a standard alkaline solution? Give reason for your answer
(iii) Fe completely reacted with dilute HCI.
I. Write an equation for the reaction
II. If 3.08g of Fe completely reacted with 50.0 cm\(^3\) of 2.20 mol dm\(^{-3}\) HCI, calculate the relative atomic mass of the metal.
(a) Acids, bases and electrolytes
- (i) According to Arrhenius, a base is a substance that dissociates in water to produce hydroxide ions (OH\(^-\)) as the only negative ions.
- (ii) Example: sodium hydroxide, NaOH (or KOH).
- (iii) I. C\(_{12}\)H\(_{22}\)O\(_{11}\) (sugar): non-electrolyte. II. NH\(_3\): weak electrolyte. III. NaOH: strong electrolyte.
- (iv) \[CH_3COOH + KOH \to CH_3COOK + H_2O\]
(b) Volume of HCl to neutralize 20.00 cm\(^3\) of 0.300 mol dm\(^{-3}\) NaOH (reaction 1:1). Moles NaOH \(= \dfrac{0.300 \times 20.00}{1000} = 6.00\times10^{-3}\) mol. Moles HCl needed = same = \(6.00\times10^{-3}\) mol. \[V = \frac{6.00\times10^{-3}}{0.500} = 0.0120\ \text{dm}^3 = 12.0\ \text{cm}^3.\]
(c) IUPAC names
- NaOCl: sodium chlorate(I) (sodium oxochlorate(I)).
- Mg(HCO\(_3\))\(_2\): magnesium hydrogentrioxocarbonate(IV) (magnesium hydrogencarbonate).
(d) Standard solution and iron
- (i) A standard solution is a solution whose concentration is accurately known.
- (ii) Na\(_2\)CO\(_3\) is the suitable one. Reason: sodium carbonate can be obtained pure, is stable and does not absorb moisture or carbon dioxide from the air, so a known mass gives an accurately known concentration; NaOH is deliquescent and absorbs CO\(_2\), so it cannot be weighed out accurately as a primary standard.
- (iii) I. \[Fe + 2HCl \to FeCl_2 + H_2\uparrow\] II. Moles of HCl \(= \dfrac{2.20 \times 50.0}{1000} = 0.110\) mol. From the equation Fe : HCl = 1 : 2, so moles of Fe \(= \dfrac{0.110}{2} = 0.0550\) mol. \[\text{Relative atomic mass} = \frac{\text{mass}}{\text{moles}} = \frac{3.08}{0.0550} = 56.0.\] So the relative atomic mass of the metal is 56.
(a) Acids, bases and electrolytes
- (i) According to Arrhenius, a base is a substance that dissociates in water to produce hydroxide ions (OH\(^-\)) as the only negative ions.
- (ii) Example: sodium hydroxide, NaOH (or KOH).
- (iii) I. C\(_{12}\)H\(_{22}\)O\(_{11}\) (sugar): non-electrolyte. II. NH\(_3\): weak electrolyte. III. NaOH: strong electrolyte.
- (iv) \[CH_3COOH + KOH \to CH_3COOK + H_2O\]
(b) Volume of HCl to neutralize 20.00 cm\(^3\) of 0.300 mol dm\(^{-3}\) NaOH (reaction 1:1). Moles NaOH \(= \dfrac{0.300 \times 20.00}{1000} = 6.00\times10^{-3}\) mol. Moles HCl needed = same = \(6.00\times10^{-3}\) mol. \[V = \frac{6.00\times10^{-3}}{0.500} = 0.0120\ \text{dm}^3 = 12.0\ \text{cm}^3.\]
(c) IUPAC names
- NaOCl: sodium chlorate(I) (sodium oxochlorate(I)).
- Mg(HCO\(_3\))\(_2\): magnesium hydrogentrioxocarbonate(IV) (magnesium hydrogencarbonate).
(d) Standard solution and iron
- (i) A standard solution is a solution whose concentration is accurately known.
- (ii) Na\(_2\)CO\(_3\) is the suitable one. Reason: sodium carbonate can be obtained pure, is stable and does not absorb moisture or carbon dioxide from the air, so a known mass gives an accurately known concentration; NaOH is deliquescent and absorbs CO\(_2\), so it cannot be weighed out accurately as a primary standard.
- (iii) I. \[Fe + 2HCl \to FeCl_2 + H_2\uparrow\] II. Moles of HCl \(= \dfrac{2.20 \times 50.0}{1000} = 0.110\) mol. From the equation Fe : HCl = 1 : 2, so moles of Fe \(= \dfrac{0.110}{2} = 0.0550\) mol. \[\text{Relative atomic mass} = \frac{\text{mass}}{\text{moles}} = \frac{3.08}{0.0550} = 56.0.\] So the relative atomic mass of the metal is 56.
