The w/v is the mass by volume concentration in percent, which tells you the mass of a certain substance (in this case diphenylcarbazide) for a specific amount of volume.

In this case a 0,5% w/v solution should contain 0,5g of substance per 100ml of liquid.

The solubility of diphenylcarbazide should be quite good in aceton, so it should all dissolve without the need to add water. The reason why water was added in the literature your citing might be because of side reactions if you use pure aceton for the rest of the method. But without knowing the specific method or experiment that is just a guess on my part.

So to sum it up: You should be good dissolving diphenylcarbazide (0,5g) in pure aceton (100ml). But the pure aceton might interfer with your experiment down stream if you dont add water.

Falco Haarnagel thank you for your help.

How much should i dilute acetone? Will it not change the concentration of the solution from 0.5%?

It will change the concentration. The level of dilution will depend on the reaction you want to perfom with it.

What do you want to use it for? If you want to use it as an indicator for the quantification of heavy metall-ions, the water might be needed as a solvent for your reaction/titration due to the bad solubility of many salts in organic solvents.

Falco Haarnagel yes I want to estimate the quantity of chromium in solution. The protocol mentioned in literature is 1 mL of 0.5% w/v diphenyl carbazide+1 mL of 0.2 M sulphuric acid and this is added to chromium solution of 2 ml and the color will change to violet and then absorbance is measured at 543 nm.

Depending on the concentration of the chromium-salt, it could fall out of solution when you add the 1,5-diphenylcarbazide solution. You could do a test with an undiluted solution. If no solid is forming you should be fine and with a calibration you then can quantify the chromium.

If some solid is forming or your soultion gets clody then you will need to add water to your 1,5-diphenylcarbazide solution. This will change the concentration however. I dont know if the method you are following acounted for that (i.e. if they want you to prepare a 0,5% Solution that you then dilute or if they want you to prepare a 1,5% solution that you then dilute with water to 0,5%).

In practical terms: i would try the undiluted 1,5-diphenylcarbazide solution first and if that doesn't work well, i would then dilute the 0,5% solution and use this together with a calibration for the quantification.

Falco Haarnagel thank you for helping out. I have run a test sample and it turned violet with chromium solution. Without the addition of water in diphenylcarbazide (just with pure acetone).

It is likely the presence of water will help to stabilise the metal ions. In the presence of pure acetone the inorganic metal may be insoluble and unavailable to react?

As per above, taking the 0,5 gram and dissolving in pure acetone, then making this up to 100ml, maybe using 50mL acetone, and then using distilled water to complete the volume requirement?