35.50 cm3 of NaOH solution is required for the complete neutralisation of a 25.00 cm3 sample of 0.200 mol dm−3 H2SO4. Calculate the concentration of the NaOH solution (in mol dm−3).

First, we need to calculate the number of moles of H2SO4. We can do this using the formula:

Moles = Concentration x Volume

For H2SO4, this is:

Moles = 0.200 mol/dm^3 x 25.00 cm^3 x (1 dm^3/1000 cm^3) = 0.005 mol

Since the reaction between NaOH and H2SO4 is a 2:1 ratio (2 moles of NaOH react with 1 mole of H2SO4), the moles of NaOH required for neutralisation is twice that of H2SO4. So, the moles of NaOH is:

Moles = 2 x 0.005 mol = 0.01 mol

Finally, we can calculate the concentration of the NaOH solution using the formula:

Concentration = Moles / Volume

For NaOH, this is:

Concentration = 0.01 mol / 35.50 cm^3 x (1 dm^3/1000 cm^3) = 0.282 mol/dm^3

So, the concentration of the NaOH solution is 0.282 mol/dm^3.