if a 10cm cube pipette were not available, which one of the following would be the best way of measuring a 10cm cube portion of a solution?

a. weigh 10 times the mass of 1cm cube of the solution.
b. weigh 10g of the solution.

I think this is a trick question. There seems to be no difference in the two answers; however, a is the correct answer. If you know the mass of 1 cc then 10x that will be the mass of 10 cc. But the mass of 1 cc of the solution, due to the temperature and density differences, may not be 1 g and 10 g may not be 10 cc. I think the unknown density of the solution is the trick part.

but if the solution is pure water, then the two answers should be both correct?

You are correct that the two answers may seem similar at first, but there is actually a key difference between them. The best way to measure a 10 cm cube portion of a solution is to use option a: weigh 10 times the mass of a 1 cm cube of the solution.

The reason for this is that the density of a solution may not be exactly 1 g/cm³. Therefore, weighing 10 g (option b) may not necessarily give you a 10 cm³ volume of the solution. However, if you know the mass of 1 cm³ of the solution, multiplying it by 10 will give you the correct mass for a 10 cm³ volume.

However, if the solution is pure water, which has a density very close to 1 g/cm³, then both options would give you the correct measurement. This is because in the case of pure water, 10 g would indeed be very close to a 10 cm³ volume.