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Author Topic: Simple inorganic tasks  (Read 1198 times)

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elementX

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Simple inorganic tasks
« on: November 16, 2018, 08:08:54 AM »

Hello.
Can you help solve four (relatively) simple tasks of some stechiometry and inorganic?

If you can't/won't attach the procedure, at least the results, please. But if you attach the procedure (or your way to solve it) i will learn (and earn skill) more.
It is for educational purpose, not industrial or commercial.

Thanks anticipately
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Borek

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Re: Simple inorganic tasks
« Reply #1 on: November 16, 2018, 08:22:51 AM »

Show the first question, show what you already did and explain where and why you got stuck, and we will start from there.
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elementX

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Re: Simple inorganic tasks
« Reply #2 on: November 16, 2018, 09:04:52 AM »

Thank you very much.
In the meanwhile i attach the task(s).

At 1 litre of a solution cointaining 0,1 moles of Potassium Acetate (CH3COOK) and 0,1 moles of  Acetic Acid (CH3COOH) i add 0,1 litres of a Sodium Hydroxide (NaOH) solution with pH 12.
Need to calculate the pH variation.
- I'm struck at "100ml of the NaOH solution" to convert in moles by taking in consideration the water moles, and how the NaOH interact with water protolisys H3O+ and the OH- in relation with its pH 12.

At 0,5 litres of a saturated solution of Silver Chloride (AgCl), i add 3 grams of Silver Nitrate (AgNO3).
Need to calculate the potential of a Silver electrode submerged into this solution. The temperature is 25° Celsius.

An organic compound consist of 60% Carbon, 13,3% Hydrogen and 27,6 Oxygen, in weight.
Need to know the "empirical formula".

A solid mix with total mass of 20 grams cointaining Magnesium and Copper being treated with 0,31 litres of a solution of 1M of Hydrocloric Acid. The molar fraction of Magnesium is 0,2.
Need to calculate the mass of the gas that generate.

I struck at early stages. I'm trying to solve myself, but lack and/or confuse the step-by-step procedure, still.
Would like an "help-model" so once i know how, i can create similar excercises mylself based on such model and practise alot until got good confidence and understanding with all.
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Borek

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Re: Simple inorganic tasks
« Reply #3 on: November 16, 2018, 01:24:58 PM »

At 1 litre of a solution cointaining 0,1 moles of Potassium Acetate (CH3COOK) and 0,1 moles of  Acetic Acid (CH3COOH) i add 0,1 litres of a Sodium Hydroxide (NaOH) solution with pH 12.
Need to calculate the pH variation.
- I'm struck at "100ml of the NaOH solution" to convert in moles by taking in consideration the water moles, and how the NaOH interact with water protolisys H3O+ and the OH- in relation with its pH 12.

Sounds like you are making it more complicated than it really is.

Assuming full dissociation, what is the concentration of NaOH if the pH of the solution is 12?
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elementX

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Re: Simple inorganic tasks
« Reply #4 on: November 16, 2018, 07:20:21 PM »

Assuming full dissociation it means totally
dissolved in [Na+] and [OH-] lites. 50% and 50%.
Thus [Na+] = [OH-] and [NaOH]~=Cb.

Kb=[OH-]² / Cb ;

[OH-]=sqrt(Kb*Cb) ;


pOH=-log10 sqrt(Kb*Cb);

pH=12-pOH == 12+ log10 sqrt(Kb*Cb)

Cannot bring the 100ml in moles to calculate the concentration.

Volume concentration nominally is 10%, but i dont think is useful, and do not take into account the other two 0,1 moles of the other two compounds (so, really, is not 10% but less).

What your way? Can you write/suggest?
I'm sure in your question there is the solving(of task), with simply, and without doing all those passages.
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Borek

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Re: Simple inorganic tasks
« Reply #5 on: November 16, 2018, 10:04:32 PM »

You are overcomplicating things and confusing simple relationship between pOH and OH- with methods for calculating pOH from known base concentration/Kb. And you already wrote

[Na+] = [OH-] and [NaOH]~=Cb

(actually the latter is quite exact).

pOH → [OH-] → C is the simple way to go.
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