Quick questions on Dilution, concentration units and pH on dilution explained: HSC Chemistry Module 6

Molarity is the default HSC unit because it links directly to stoichiometry ($n = cV$). The other units appear in environmental and biological contexts (lead in drinking water, residual chlorine, salinity).

If you need a very dilute solution, a single one-step dilution can be inaccurate (pipetting a very small volume). Serial dilution does it in stages: each step is a 10- or 100-fold dilution. To go from 1.00 mol/L to $1.00 \times 10^{-4}$ mol/L, do four successive 10-fold dilutions.

A 10-fold dilution raises pH by:

State the dilution equation $c_1 V_1 = c_2 V_2$ and explain why moles of solute are conserved on dilution. [2 marks]

Calculate the volume of concentrated 18.0 mol L$^{-1}$ $H_2SO_4$ required to prepare 500 mL of 0.250 mol L$^{-1}$ acid. [2 marks]

A 0.10 mol L$^{-1}$ solution of HCl and a 0.10 mol L$^{-1}$ solution of acetic acid (pKa = 4.74) are each diluted 100-fold. (a) Calculate the pH of each before dilution. (b) Calculate the pH of each after dilution.