Standardising 100mL of 0.5M NaOH with HCl?

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Standardising 100mL of 0.5M NaOH with HCl?

Postby Limobean » Thu Oct 25, 2012 12:51 am

I am really confused how to perform calculations on how to create 0.5M NaOH.
I actually have to create this concentration to perform an acid-base titration to find how much acid there is in different types of viegar.

Our school has NaOH pellets, and HCL, but I don't know the concentration.
I am unsure how to create this concentration? I've searched online, but I can't find any websites that explain it in simple terms.
Please help? Also could you provide working out so I can see what's happening? And also a formula if there is one?

Thanks!
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Re: Standardising 100mL of 0.5M NaOH with HCl?

Postby edneu3 » Thu Oct 25, 2012 8:58 am

Hi,

Are you working on a science project or trying to figure out a problem for a school chemistry class?

If you are working on a school chemistry class problem, it would be best to work directly with your instructor to learn how to formulate molal mixtures.

If you are working on a science fair project, it would be best to give us a bit more background about what you are trying to do.

Here are some internet sites that may provide some useful additional information for you:

http://cnx.org/content/m16618/latest/

https://chemistry.twu.edu/tutorial/MolalitySum.html

http://www.chemteam.info/Solutions/Molality.html

http://www.ausetute.com.au/molality.html

Good luck with your project.
Ed Neu
Buffalo, MN
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Re: Standardising 100mL of 0.5M NaOH with HCl?

Postby Craig_Bridge » Thu Oct 25, 2012 3:12 pm

I can't believe that you have to prepare your own solutions from pure NaOH pellets. Most chemistry labs make stock 1.0M solutions from which to start.

Making NaOH stock solutions from NaOH pellets is DANGEROUS if you have never been taught how to do it and all of the safety proceedures requred. Full face shields, rubber protective gloves, rubber apron, safety sink, eye wash station, etc....

ONLY DO THIS WITH DIRECT SUPERVISON OF THE PERSON IN CHARGE OF THE LAB!
Adjust your quantities based on how many mL of stock solution your supervisor wants you to make!

What is the molecular weight of NaOH? You have the chemical formula, given your on this web site, you have internet access to the molecular weights of the atoms Na, O, and H. You should be able to do this step yourself. Post your answer and we can cross check it.
By definition, a 0.5M NaOH aqueous solution is 0.5 x molecluar weight disolved in 1 liter of pure water.

Put 1 liter of pure water into a clean 1.5 liter pyrex flask. Dry out a safety sink and place the flask on the bottom of the sink to one side.

CAUTION: Disolving NaOH in water is an exothermic reaction that will generate a considerable amount of heat!
Keep all surfaces and equipment used to prepare the NaOH completely DRY!
Work on a surface that drains into your DRY safety sink that will contain any spills should you have an accident.
Weigh out 1/2 a mole of NaOH pellets, grind in mortar with a pestle. SLOWLY add and stir small amounts of the NaOH into 1 liter of pure water in a pyrex flask allowing for the solution to cool before adding more.

Place the newly made stock solution somewhere safe and clear of your work area.

Clean up your work area and all of your equipment to make sure you didn't leave any traces of NaOH behind.

I SUSPECT that your teacher just wants you to do the calculations as a learning exercise and isn't actually going to have you make the stock solution!
-Craig
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