# Thread: Within the next 3 hours

1. Senior Member Community Builder
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## Within the next 3 hours

Can someone explain to me one or more of the following...

1. Normal Saline, which is a 0.85% solution of sodium chloride in water (0.85g of solute per 100g of water.) What is the molar concentration of normal saline?

2. A current of 1.00A passes for 96.5 hours through molten anhydrous calcium chloride. What is the mass of calcium deposited?

3. A excess of magnesium carbonate was added to 50.0cm^3 of 1.00mol/dm^3 sulphuric acid. Calculate:

a) the mass of magnesium carbonate that reacted

b) the volume at r.t.p. of carbon diocide evolved.

...My chemistry exam is tomorrow... I am on my knees for help...

2. Senior Member Always Around
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which board are you taking? I'm doing chem tomorrow and I have no idea how to do 2. anyway

1. 1g of water takes up 1cm^3. 1 dm^3 is 1litre, 1 litre is 1000cm^3. so if there is 0.85g in 100cm^3, there is 8.5g in 1dm^3.
molar mass of NaCl is 58g. 8.5/58 =0.147 (3sf). so 0.147mols/dm^3

3a)since the conc. is 1mol/dm^3 and there is 50cm^3 of it, there is 50/1000 mols of acid
molar mass of magnesimu carbonate = 84g. 50/1000 * 84 = 4.2g

b) at room temp + normal pressure, 1mol of gas takes up 24000cm^3.
the molar mass of CO3 is 60g. 50/1000 * 60 = 3g
of this 3g that reacts, only 2.2 becomes CO2.
so 24000 * 2.2/44 =1200cm^3

edit: I think those are correct but it would be better if there are any college majors or something out there that they confirm it.
edit2: I love you Quira.
Last edited by jamie1990; 06-12-2007 at 11:50 AM. Reason: <3

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Your
1. was correct
2. nooope... it was 72 g :/
3. a. was 650cm^3
b. was 700cm^3 :S

Oh god, I'm gonna fail.
And are you taking GCSE?
Mine's the ermm AQA board D:

p.s. 'I love you, Quira.' ... WTF?!

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yes I am, the board I'm taking is Edexcel.
how could 3a be 650cm^3? it was aking for a mass.
How did you get 700cm^3 for 3b?

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^I have no idea.
I think I might just pray that any calculation questions aren't too hard.
Haha, gutted on you. Edexcel is way harder than AQ apparantly. =]

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Really? heh, I shouldn't be surprised. But at least with Edexcel you don't need to know about electrolysis in such detail.
With calculations, just remember to convert everything to mols and to keep the units throughout the equation so you don't lose track of it.
Good luck my love! I hope I have been of some small help!

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Good luck guys

I'd help you out, what with my chem A level next week, but seems like you've got it figured out.

8. good luck :3

i have not touched chemistry for years and have forgotten everything so i can't help, sorry

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My god.
I think I may be having a panic attack.
I don't understand these calculations at all.
And I only vaguely know who Arrhenius and the Bronsted-Lowry people are.
One of them are British. ;AILHOAISDDDD

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WTF Quira, that sounds like AS level shit that I do.

Edit: Now I'M having a panic attack.

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