# AS Level Chemistry Calculations HELP

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#1
Hi, I'm an alevel chemistry student. Ive just started as level chemistry and I'm struggling with the calculations .. such as ideal gas, titration, hydration (calculating the interger of water in an anhydrous compound), molecular formula. My exam board is AQA, specification is Chemistry A.
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5 years ago
#2
Hi there!

Chemistry really is about two things:
1) Calculations
2) Processes

The calculations are possibly the easiest to understand, but the toughest to master.

Some are really straight forward once you know them:

Ideal Gas Equation:
PV=nRt

So learn this equation and on every question write it down before you answer it. Rearrange the equation to whatever you are trying to find.
P = Pressure (Pa)
V = Volume (m3)
n = number of moles (if not, use m/Mr)
R = constant (given as 8.31)
t = Temperature (K)
Just solve for the unknown! (If the question is wordy, do what I do with SUVAT in physics and write out all of the values)
Titration
This one requires two equations: c=n/v (v in dm3) AND n=m/Mr
If you learn these, just write out the values you know and find the ones you don't. When doing this, find the molar ratio by writing out the balanced equation.

We haven't done hydration yet, so I'll pass on that

Molecular Formula
I assume here we're talking about empirical to molecular? If so, just find Mr of the molecule, and Mr of the empirical and then multiply the numbers in subscript in the empirical formula by the number you just calculated.

Just learn the equations and really practise. Hope this helps, and if you have any more problems just let me know.
1
#3
(Original post by Tobybeta)
Hi there!

Chemistry really is about two things:
1) Calculations
2) Processes

The calculations are possibly the easiest to understand, but the toughest to master.

Some are really straight forward once you know them:

Ideal Gas Equation:
PV=nRt

So learn this equation and on every question write it down before you answer it. Rearrange the equation to whatever you are trying to find.
P = Pressure (Pa)
V = Volume (m3)
n = number of moles (if not, use m/Mr)
R = constant (given as 8.31)
t = Temperature (K)
Just solve for the unknown! (If the question is wordy, do what I do with SUVAT in physics and write out all of the values)
Titration
This one requires two equations: c=n/v (v in dm3) AND n=m/Mr
If you learn these, just write out the values you know and find the ones you don't. When doing this, find the molar ratio by writing out the balanced equation.

We haven't done hydration yet, so I'll pass on that

Molecular Formula
I assume here we're talking about empirical to molecular? If so, just find Mr of the molecule, and Mr of the empirical and then multiply the numbers in subscript in the empirical formula by the number you just calculated.

Just learn the equations and really practise. Hope this helps, and if you have any more problems just let me know.
Thank You soo much!!! Great HELP
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