[alexbold]

Good day
I know it's an easy question and even I can google it. but the problem actually started when I searched it in the web.
Please make it easy to understand. I just want to make 10% sodium hydroxide solution. what should be the proportion of milli-q water and NaOH? let's say I want 200 ml of 10% sodium hydroxide solution.
PLEASE don't make it complicated.

Regards.

[chenbeier]

You have to convert the 200 ml to the mass.Need specific Gravity for this. In a table book you can find it.
In this Case it would be 1,1089 g/ ml
Now you can calculate the mass. 10% of it is the mass of solid NaOH and 90% is the water.

[Borek]

This gets a bit convoluted when you aim at an exact volume, but as long as it doesn't matter much - what would be the concentration if you mix 180 g of water with 20 g of NaOH?

[alexbold]

This gets a bit convoluted when you aim at an exact volume, but as long as it doesn't matter much - what would be the concentration if you mix 180 g of water with 20 g of NaOH?

This was the thing that I was thinking. But the problem actually started when I saw in some web pages that they said 20 g in 200 ml.

[mjc123]

People sometimes use % to mean "% weight/volume". That is, a 10% w/v solution contains 10 g solute in 100 mL solution. But it is also used to mean % w/w, i.e. 10 g solute in 100 g solution.
Using it without specifying which, as in "10% NaOH solution", is ambiguous - it could mean either.

[billnotgatez]

@mjc123 or anyone else with an opinion.

Many times I have seen that  1 ml of water is assumed to be 1 g of water. Is this just sloppy or reasonable.

I pose this to give @alexbold some context to his question.

Bill

[Borek]

Many times I have seen that  1 ml of water is assumed to be 1 g of water. Is this just sloppy or reasonable.

That's how originally 1 g was defined - mass of 1 cubic centimeter of water at the melting point. Later it was changed to 1 cubic centimeter of water at 4°C. 1 cubic centimeter and 1 mL are (or at least were at some point, I believe definitions were changing several times) exactly the same thing.

Potential problems stem from two facts:

1. We rarely work at 4°C, and at room temperature of 20°C mass of 1 mL of water is not 1 g but 0.9982 g - error of 0.2%, for most applications completely negligible.

2. We often assume the same 1 g per 1 mL not only for water, but also for solutions. As long as they are diluted this is often a reasonable estimate, but you need to know what you are doing to be sure.