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# Sodium Hydroxide: How to make to 0.5 M strength

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A 'molar solution' or '1.0 M' solution is defined as a solution which contains one gram-equivalent weight of the substance in question dissolved in 1 liter of solution (the water).

The atomic weight of a molecule of sodium hydroxide, NaOH, would be the atomic weight of 1 atom of Na plus 1 atom of O plus one atom of H (the atomic weights can be obtained from the Periodic Table, or an appendix in the Metal Finishing Guidebook) as

22.997 + 16.000 + 1.008 or 40.005

-- let's round it to 40.

So a 1.0 M solution of sodium hydroxide contains 40 grams of sodium hydroxide per liter of water. Working with different strengths like 0.5 M (1/2 molar or 20 g/L) and different volumes is then a matter of simple arithmetic.

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Current postings:

October 11, 2021Q. How to prepare 0.5 Mole of NaOH - to make 20 ml of solution.

My Query: Is it correct [we know that 0.5M NaOH is equal to 20 grams - it was dissolved in 20 ml of water] this statement is correct or not ? Please reply sir!

Researcher - Tamil Nadu

October 2021

A. Hi Dr. Paul. The statement is incorrect.

We've now added a 'Tutorial' sidebar at the top of the page explaining the concept and offering the bottom line answer that a 1.0 M solution of sodium hydroxide contains 40 grams of sodium hydroxide per liter (1000 mL) of water, and the rest is simply arithmetic.

Luck & Regards,

Ted Mooney, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

*<- Ed. note: No abstract
questions please!
Please tell us YOUR
situation. What? Huh?*

Q. Hi There. May I please have help with the following?

How many mL of water must be added to 10 grams of NaOH to make a 0.50 molar solution?

- Los Angeles, California

May 2022

A. Hi Connie. We explain on this page how/why a 1.0 molar solution is 40 g of NaOH per 1000 mL, and that a 0.5 molar solution would be 20 grams per 1000 mL. If that doesn't do it for you, what step in the arithmetic are you having trouble with?

But for safety, never *"water must be added"* to NaOH -- you add the NaOH to the water :-)

Luck & Regards,

Ted Mooney, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

May 17, 2022

Much appreciated! Thank you!

Connie Pierson [returning]- Los Angeles, CA

May 20, 2022

Q. I need to prepare 0.5 mol solution of NaOH from a prepared 1 mol solution of NaOH. I have no solid NaOH and need to prepare this in a volumetric flask, and I want to find out how much 1 mol NaOH and how much water I need to mix.

Dozer Peters- Iowa

May 2022

A. Hi Dozer. That would depend on how much of it you need to prepare, wouldn't it?

When you understand what a "1 mol" solution actually means, and what a "0.5 mol" solution actually means, the answer will be very obvious, and we are happy to take as much time trying to explain this as you need. But it would be a disservice for us to tell students whether to divide by two or to multiply by two so they can answer their homework questions without them putting in any effort to understand the question. Let's put in equal parts here.

Luck & Regards,

Ted Mooney, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

Closely related Q&A's, oldest first:

2002Q. Hello Folks,

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

Thanks,

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

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 2002 A. Dissolve 20 g NaOH to a total volume of 1 L in water. James Totter, CEF - Tallahassee, Florida |

2002
A. Dear Mr Arroyo, One mole of NaOH weighs 23(Na)+16(O)+1(H)=40 g Kind regards, Sjamp van Esch - Eindhoven, The Netherlands 2002 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 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 cousin Angel. A "half molar" solution is exactly the same as a "0.5 M" solution, so this was already answered by 4 helpers. If you remain confused, please explain in what way these answers are proving unsatisfactory. Thanks.

Regards,

Ted Mooney, P.E.

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

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

Jelo, I know that you know that to make half as much quantity of *anything*, you just use half as much of the ingredients.

I think these students are just pulling our leg now, rather than being unable to divide by two. Thank god I didn't go into teaching; I wouldn't last the first period :-)

Regards,

Ted Mooney, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

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?

- Abu dhabi, UAE

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

Regards,

Ted Mooney, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

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.

Regards,

Ted Mooney, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

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 cousin Umahi. The calculation for this has been explained 6 times on this page now. Please take the time to read it then tell us what it is that you are not understanding. I'd 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 start working with hazardous chemicals. Good luck.

Regards,

Ted Mooney, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

**"Standard Methods for Examination of Water & Wastewater"**

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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

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?

- 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.

Regards,

Ted Mooney, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

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Ed. note: If any reader is having difficulty understanding how to do such calculations, please **explain your difficulty, what you are not following**, and we will certainly be happy to try to clarify things for you so you fully understand! But we've been receiving many inquiries lately asking for the answers with nothing at all changed but the numbers -- in others words, asking us to do the arithmetic of multiplying or dividing. Sorry, but we must move forward and discard arithmetic questions or this discussion would stay mired forever at 3rd grade level. Apologies.

March 31, 2020

Hi Ted,

Happy to see your patience in Answering all these questions ... Thank you :-)

Hope you and your family are safe from this Corona Pandemic.. Take Care and my prayers that you get plenty of health, wealth and happiness.

- Anand, Gujarat, India

April 2020

Thank you cousin Rahul!

My wife and I are fortunate to live in a private house in a pleasant suburb with the ravages of this pandemic safely outside of the gate of our comfortable little world so far. The internet has been treating us kindly so far, letting me administer the site without venturing outside of home. I wish you and yours an easy passage through this trying time.

Regards,

Ted Mooney, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey