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# Concentration of chemicals watch

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1. Is there a maximum concentration (in moles) in secondary school science labs of the concentration of chemicals? If so, what is it? I am doing a mock coursework on the sulfur clock so what concentrations of sodium thiosulfate and Hydrochloric acid should I put in the method. Thank you in advance!
2. Yeah 70% I think.
3. (Original post by caitlinford3)
Yeah 70% I think.
Thank you, would you be able to say it in moles?

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4. (Original post by laur.m)
Thank you, would you be able to say it in moles?

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The amount of moles depends on the volume of the acid, I just know the concentration is 70%. You should use the titration method to work out the number of moles using the chemical formula & whatever volume you are asking of
5. (Original post by caitlinford3)
The amount of moles depends on the volume of the acid, I just know the concentration is 70%. You should use the titration method to work out the number of moles using the chemical formula & whatever volume you are asking of
Ah, we have not done titration yet, I am assuming it is in unit 3? If I was reacting 50cm3 sodium thiosulfate and 5cm3 Hydrochloric acid, would you be able to possibly explain how you use this formula to say the maximum for each?

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6. (Original post by laur.m)
Ah, we have not done titration yet, I am assuming it is in unit 3? If I was reacting 50cm3 sodium thiosulfate and 5cm3 Hydrochloric acid, would you be able to possibly explain how you use this formula to say the maximum for each?

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Yeah it's in unit 3
Basically, to do a titration reaction you should write out both compounds first with their formula then write the labels 'moles, volume, concentration) under BOTH.

Na2S2O3 (Sodium Thiosulphate)
moles -
volume -
concentration -

HCl (Hydrochloric acid)
moles -
volume -
concentration -

Now, as we can see there is no integer (the whole number before the formula, there is a proper name for this but I've totally forgotten it atm lmfao) it means the ratio of the two compounds is 1:1, if one of them had a 2 infront it would be 2:1, if one had a 2 infront and one had a 3 infront it would be 2:3 and so on. Usually at GCSE they will only make the compound 1:1 as you don't get the formula for this so it's alot to remember.

Okay, so now you fill in the 'volume, concentration' with all the information you've been given in the question. Whichever you have the information of both the volume and concentration for, is the one we will work with.

Something you MUST remember is that you can only write the concentation in dm3. Like in your question, they do sometimes give it in cm3 and if you wrote that you'd lose marks basically. To get to dm3 from cm3 you do cm3 / 1000.
(I have divided them both by 1000 and wrote them as dm3 below)

ratio 1:1
Na2S2O3 (Sodium Thiosulphate)
moles -
volume - 0.05dm3
concentration -

HCl (Hydrochloric acid)
moles -
volume - 0.005dm3
concentration -

Now I've got to this point and realised you didn't say a concentration for any lmfao! Do you have a concentration for either or am I working with the 70% concentration I suggested?
7. (Original post by caitlinford3)
Yeah it's in unit 3
Basically, to do a titration reaction you should write out both compounds first with their formula then write the labels 'moles, volume, concentration) under BOTH.

Na2S2O3 (Sodium Thiosulphate)
moles -
volume -
concentration -

HCl (Hydrochloric acid)
moles -
volume -
concentration -

Now, as we can see there is no integer (the whole number before the formula, there is a proper name for this but I've totally forgotten it atm lmfao) it means the ratio of the two compounds is 1:1, if one of them had a 2 infront it would be 2:1, if one had a 2 infront and one had a 3 infront it would be 2:3 and so on. Usually at GCSE they will only make the compound 1:1 as you don't get the formula for this so it's alot to remember.

Okay, so now you fill in the 'volume, concentration' with all the information you've been given in the question. Whichever you have the information of both the volume and concentration for, is the one we will work with.

Something you MUST remember is that you can only write the concentation in dm3. Like in your question, they do sometimes give it in cm3 and if you wrote that you'd lose marks basically. To get to dm3 from cm3 you do cm3 / 1000.
(I have divided them both by 1000 and wrote them as dm3 below)

ratio 1:1
Na2S2O3 (Sodium Thiosulphate)
moles -
volume - 0.05dm3
concentration -

HCl (Hydrochloric acid)
moles -
volume - 0.005dm3
concentration -

Now I've got to this point and realised you didn't say a concentration for any lmfao! Do you have a concentration for either or am I working with the 70% concentration I suggested?
That seems so confusing (really not looking forward to unit 3!) I think I have found a method that uses concentrations of 0.1M, 0.2M, 0.3M and 0.4M for sodium thiosulfate solution and 2M for the Hydrochloric acid so I assume that they are appropriate, however I appreciate your explanation and will refer to it when I get bamboozled by titration in a couple of months thank you for your help!!!

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8. (Original post by laur.m)
That seems so confusing (really not looking forward to unit 3!) I think I have found a method that uses concentrations of 0.1M, 0.2M, 0.3M and 0.4M for sodium thiosulfate solution and 2M for the Hydrochloric acid so I assume that they are appropriate, however I appreciate your explanation and will refer to it when I get bamboozled by titration in a couple of months thank you for your help!!!

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No problem! It is confusing but I personally feel like it's one of the easiest things on unit 3 because unit 3 is such a killer haha!

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