Tap water contains a number of dissolved chemicals - Scottish Highers Chemistry - Question 7 - 2023

The term used to describe this part of the molecule is "ionic."

To calculate the concentration of calcium ions:

1. Calculate the moles of EDTA used:

   $\text{Moles of EDTA} = \text{concentration} \times \text{volume} = 0.0045 \text{ mol dm}^{-3} \times 0.0093 \text{ dm}^{3} = 4.185 \times 10^{-5} \text{ mol}$

2. Moles of calcium ions: From the balanced equation, the mole ratio of Ca²⁺ to EDTA is 1:1. Thus, moles of Ca²⁺ = moles of EDTA = $4.185 \times 10^{-5} \text{ mol}$.

3. Calculate concentration of Ca²⁺ in the original water sample:

   $\text{Concentration of Ca}^{2+} = \frac{\text{moles}}{\text{volume}} = \frac{4.185 \times 10^{-5} \text{ mol}}{0.0500 \text{ dm}^{3}} = 0.000837 \text{ mol dm}^{-3}$

To estimate the concentration of permanganate ions based on the absorbance:

1. Plot an appropriate line of best fit on the given graph.
2. From the graph, for an absorbance of 0.08, the estimated concentration of permanganate ions is approximately between 4.4 and 5.4 mg dm⁻³.

Trichloromethane (CHCl₃) is polar because of the presence of a permanent dipole due to the asymmetric distribution of charge, with one hydrogen atom providing a slight positive charge. On the other hand, tetrachloromethane (CCl₄) is non-polar, as it has a symmetrical tetrahedral structure where the dipoles from the four chlorine atoms cancel each other out, resulting in no overall dipole moment.

To calculate the enthalpy change:

1. Use bond enthalpy data to find the energy required to break the bonds in the reactants and the energy released in forming the bonds in the products.

2. The enthalpy change can then be calculated using:

   $\Delta H = \text{Energy of bonds broken} - \text{Energy of bonds formed}$

3. If the bond enthalpy calculations give an answer of approximately -14 kJ mol⁻¹, write the final answer as -14 kJ mol⁻¹.