Keep in mind that you are doing percent volume, rather than percent weight.

Here you are assuming that 1 gram of anything = 1 ml.

That is close...

However, the density of Ethanol is .789 g/cc, rather than 1 g/cc.

Hmmm

500ml of vodka will have to weigh less than 500ml of water, so it would have to weigh less than 500g. Somewhere the 1220g must be wrong. Did you weigh the bottle?

Anyway, the first thing to do is to figure out how much water, and how much alcohol you have.

500ml * 0.625 = 312.5 ml (g) water.

500ml * 0.375 = 187.5 ml alcohol

187.5 ml * .789 g/ml = 147.9 g ethanol.

Total: 312.5 g water + 147.9 g ethanol = 460.4 g solution.

Add 200g --> 660.4 g solution.

**WEIGHT Percent Ethanol = 147.9 g / 660.4 g = 22.4%**

If you wanted to calculate volume percent, you would need to know the volume of the sweets in the solution.

The density of sugar is about 1.59 g/cm³. However, my guess is that the density in solution is closer to 2 g/cm³.

So, let's put in 100cm³ = 200g of sweets in solution as an estimate

From above:

312.5 ml (g) water

187.5 ml alcohol

500 ml solution.

Add 100 ml sugar (approx).

600 ml final solution (approx).

**Volume Percent Ethanol 187.5 ml / 600ml = 31.2% (approx).**