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topic 17894

Sodium Hydroxide: How to make to 0.5 M strength

A discussion started in 2002 but continuing through 2017


Q. Hello Folks,

Can anybody help me to make a 0.5 M NaOH solution, I forgot that formula?


Reynaldo Arroyo
- Valencia, California, U.S.A.

simultaneous 2002

A. NaOH has a valence of 1, so molar and Normal are the same. One mole of NaOH in one Liter of pure water = 1 N. Since you want 0.5, use 1/2 mole (20.0 grams) of NaOH. If this is for a titration, you will need to standardize it. By the time you make it up, filter it (if required), cool it and then standardize it, you will find that it is cheaper to buy the premade solution from VWR-SP or Fisher or ?.

James Watts
- Navarre, Florida


A. Dissolve 20 g NaOH to a total volume of 1 L in water.

James Totter
James Totter, CEF
- Tallahassee, Florida

simultaneous 2002

A. Dear Mr Arroyo,

One mole of NaOH weighs 23(Na)+16(O)+1(H)=40 g
A 0.5 M NaOH is then 20 g NaOH/L.
So dissolve 20 g NaOH in 500 ml water let it cool down to room temperature and fill it up to one liter. For accurate results you can use an analytical balance and a volumetric flask.

Kind regards,

Sjamp van Esch
Sjamp van Esch
- Eindhoven, The Netherlands


A. M means Gram Molecular Weight, so 0.5 M means half the gram molecular weight of the chemical. In the case of NaOH the mole. wt. is Na=23, O = 16, H =1, so NaOH = 40. Half of that is 20, so 0.5 M NaOH is the same as 20 g/l. I trust you now remember your basic chemistry.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

September 17, 2013

Q. Please help me with my research: How are we going to prepare a half molar NaOH?

Angel de Silva
- Davao City, Philippines

September 23, 2013

A. Hi Angel. A "half molar" solution is the same as "0.5 M", so this was already answered 4 times. If you are still confused, please explain in what way these answers are proving unsatisfactory. Thanks.


Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey
We need "Aloha" now more than ever

March 26, 2015

A. To make 0.5 M of NaOH, measure 20 g of sodium hydroxide and dissolve it in 1000 ml of water; we have used 20 g because the RMM [relative molar mass] of NaOH is 40 and we are making 0.5 M solution.

cyprian nthuli
- mombasa , kenya

September 29, 2015

Q. How many grams NaOH are needed to prepare 500 ml of 0.5 M NaOH

jelo pabular
- Cebu city, Philippines

thumbs up signI think these students are just pulling our leg now, rather than not knowing how to divide by two. Thank god I didn't go into teaching :-)


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Ted Mooney, P.E. RET
Pine Beach, New Jersey
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December 20, 2015

Q. Dear Friends,
I have a Query regarding the Sodium hydroxide solution preparation. I prepared the sodium hydroxide solution with respect to 15 gram per liter and poured into a glass bottle, after 2 days I titrated it to find out the concentration of NaOH and surprisingly found that NaOH conc. reduces to 10 g/l and even I found aluminum as 4 g/l, so can somebody explain me how this aluminium introduced into this solution?

Aijazullah Tajir
- Abu dhabi, UAE

A. Hi Aijazullah. It's obviously either experimental error or a jar which contained reactable aluminum. Good luck.


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Ted Mooney, P.E. RET
Pine Beach, New Jersey
We need "Aloha" now more than ever

April 20, 2016

Q. How to make 20% sodium hydroxide solution from a 1 Normal solution?

Tammy Lee
- Birmingham, Alabama, USA

April 2016

A. Hi Tammy. As you can see from the 5 explanations above, your 1N solution is 40 g / 1000 g or 4% by weight. You could heat it and evaporate the water until it was 20% NaOH by weight, but I doubt that evaporating the water from a dilute caustic solution to make a more concentrated and dangerous one would be approved by your university these days though. Good luck.


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Ted Mooney, P.E. RET
Pine Beach, New Jersey
We need "Aloha" now more than ever

April 3, 2017

Q. How do I prepare 0.4 mol/l of NaOH? Someone help please.

UMAHI O [last name deleted for privacy by Editor]
diagnostic center - Nigeria

April 2017

A. Hi Umahi. The calculation for this has been explained 6 times on this page now. Please take the time to tell us what it is that you are not understanding. I would be worried about the sufficiency of my haz-mat training if I were you because this is pretty basic stuff you should know before you work with hazardous chemicals. Good luck.


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Ted Mooney, P.E. RET
Pine Beach, New Jersey
We need "Aloha" now more than ever

"Standard Methods for Examination of Water & Wastewater"
from Abe Books

April 3, 2017

A. The best way is to make a 50% w/w solution of NaOH in DI water, allow it to cool, let any solids settle out (Na2CO3) and then weigh out 8.0 g of this prep into a volumetric flask. Make up to the mark with DI, with lots of swirling, let cool, then make up to the mark again.

For maximum accuracy, a standardization vs. KH pthalate would be advisable. Check "Standard Methods" for this procedure.

This is really kind of basic Chem 101 stuff, if I may say.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

April 4, 2017

Q. I have a 5% solution of Sodium Hydroxide w/v.
I would like a 1.5% solution of Sodium hydroxide.

How do I solve this?

Stan Ihori
- Tualatin, Oregon, USA

April 2017

A. Hi Stan. I guess you're saying you have a solution with 50 grams of NaOH for every 1000 mls? And you would like to dilute it to the point where you have only 15 grams of NaOH for every 1000 mls?

So for every 15 mls of solution of 5% solution you wish to dilute, add 35 mls of water to end up with 50 mls of 1.5% solution.


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Ted Mooney, P.E. RET
Pine Beach, New Jersey
We need "Aloha" now more than ever

Ed. note: If any reader is having difficulty understanding how to do such calculations, please explain your difficulty and we will try to clarify things for you. But we've been receiving many inquiries asking for the answers with nothing changed but the numbers -- in others words, asking us to do the arithmetic -- and we have been discarding them.

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