O Calculations

Question 1

What is the equation for enthalpy change of solution?

Answer 1

Question 2

How do you work out pH of a strong acid?

Answer 2

1. Write out an ionisation expression for the acid
2. Use molar ratios to deduce the [H+]
3. Substitute into pH = -log[H+]

Question 3

How do you work out the pH of a weak acid?

Answer 3

1. Write out the Ka expression for the weak acid
2. Assume that [H+] is the same as [A-]
3. Rearrange to make [H+] the subject
4. substitute into pH = -log[H+]

Question 4

How do you work out pH of a strong base?

Answer 4

1. Write out ionisation expression for the base
2. Use molar ratios to deduce the [OH-]
3. Substitute [OH-] into Kw
4. Rearrange to [H+] the subject
5. Substitute into pH = -log[H+]

Question 5

How do you work out pH of a buffer solution?

Answer 5

1. Write out the Ka expression for the buffer
   [A-] = salt [HA] = weak acid
2. Recalculate the concentrations of HA and A- in the new total volume of the buffer (C1 x V1 = C2 x V2)
3. Rearrange to make [H+] the subject
4. Calculate H+
5. Substitute into pH = -log[H+]

Question 6

How do you work out enthalpy change of a reaction from experimental data?

Answer 6

Question 7

How do you calculate the minimum temperature a reaction is feasible at?

Answer 7