This is quite difficult if titration is not allowed. Here are some of my thoughts.

Drying the solution to dryness isn’t a good method in this case as you lose the water for dissolving the acid.

An alternative method is to do filtration, but then we would have to find out the type of acid used using a small sample of acid (whether it is nitric acid, hydrochloric acid etc).

In this case, we would need to put in as much of the, say, 20 g of powdered magnesium oxide to allow complete reaction, before we proceed to find the mass of the unreacted powdered magnesium oxide after drying and so on.

It’s just my line of thought, but this may not be the best answer or may not even be a correct answer.

What I would do is this. A quick, rough plan.

1. Test out the type of acid

2. Prepare a sample of 100.0 cm3 of acid using 4 x 25.0 cm3 burette (they mentioned no titration method, but they never mentioned we are not allowed to use the apparatus in titration)

3. Prepare say 100 g powdered magnesium oxide (or calcium carbonate etc, but maybe 100g is too much)

4. Add all the 100g powdered magnesium oxide into the acid, stir/shake, filtrate the mixture to filter out the unreacted magnesium oxide and wash/dry it

5. Measure the mass of the unreacted magnesium oxide

6. Calculate mass of reacted magnesium oxide, from there we work out the mass of acid

7. From there we can compute the concentration

thank you :)

If you use carbonate, you also also measure the volume of carbon dioxide produced.

In any case, make sure to write in that the experiment is repeated at least twice. And that average of the three (or more) readings is taken to find the average concentration