SWIMfriend said:The problem is that the statement: "Add 25 ml of water with 5 ml of 10% HCl solution" is ambiguous.
does with mean containing?
"Add 25ml of water CONTAINING 5 ml of 10% HCl solution": in which can you end up with 25ml of 2% HCl
or does with mean AND?
"Add 25ml of water AND 5 ml of 10% HCl solution": in which can you end up with 30ml of 1.66% HCl
The proper way to say it is to simply state the percentage and quantity: "Add 25ml of 2% HCl"
It's best to say it that way, because different people may be using different concentrations (as in this case, where somebody has 25% HCl), so it more easily allows for different people to understand what's required and calculate based on what they have in stock.
Over to 69ron, to tie it all together and make this the most elegantly worded theoretical recipe ever.