Chapter 3 Calculations
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What is a Mole?
The number of atoms in 12g of Carbon-12
How do you calculate the number of atoms in Zg of X
Find the number of moles by N=M/Mr Multiply by Avagadros constant (6.02x10^23)
What is molar mass?
Mass per mole of a substance
What is empirical formula?
Simplest whole number ration of atoms of each element in a compound
What are the parts of a hydrated salt?
Water=Water of crystallisation Salt= Anhydrous Salt
Why might an experiment to calculate moles of water in a hydrated salt be incorrect?
Not all of the mass of water is removed The salt may have decomposed
Formula link V, N , and C
N=cV
What is the molar gas volume?
The volume per mole of gas molecules at a stated temperature and pressure (at RTP 24dm3)
What are the conditions are RTP?
298K 100KPa
What is the ideal gas equation?
pV=nKt Pressure (pa) x Volume (m3)= Moles x Gas constant x Temperature (Kelvin) Gas Constant = 8.314 +273 to convert celcius to Kelvin
What is Stoichiometry?
The ratio of the amount, in moles, of each substance in a chemical reaction
What is the formula for percentage yield?
(Actual Yield/ Theoretical Yield ) x 100
What is the formula for atom economy ?
(Mr of desired product/ Mr total products) x 100
What would happen to the water of crystallisation coefficient if not all of the water was removed in the experiment?
Too small Not all of the water is removed so it would appear to be smaller than it is
What would happen to the coefficient of the crystallisation of water in the experiment if some of the salt decomposed?
Too large The mass of water lost is too large, as some of the salt which is lost is perceived as lost water, making x too large
How can you improve the accuracy of heating to collect gas in a gas syringe?
Heat until the volume does not change Wait for the syringe to cool before measuring volume
A hydrated salt is heated until some of the water is removed. Given the mass of the water lost and original hydrated salt, how can you calculate the formula for the remaining salt?
n=m/mr for original salt and water lost Write an equation for the decomposition For 0.02 mol of salt, 0.08 mol water So ratio 1:4, 4 waters lost from the original salt So if started at .8 H20, now .4H20
How can you decrease the percentage uncertainty of the heating till constant mass experiment? How do you measure percentage uncertainty for this experiment?
Use a larger mass of the salt Use a scale which is more precise and more accurate (Mass of water loss (not of salt or of crucible, need to calculate water loss) / uncertainty) x 2 (or number of readings) x 100