Chapter 3 Calculations

Question 1

What is a Mole?

Answer 1

The number of atoms in 12g of Carbon-12

Question 2

How do you calculate the number of atoms in Zg of X

Answer 2

Find the number of moles by N=M/Mr
Multiply by Avagadros constant (6.02x10^23)

Question 3

What is molar mass?

Answer 3

Mass per mole of a substance

Question 4

What is empirical formula?

Answer 4

Simplest whole number ration of atoms of each element in a compound

Question 5

What are the parts of a hydrated salt?

Answer 5

Water=Water of crystallisation
Salt= Anhydrous Salt

Question 6

Why might an experiment to calculate moles of water in a hydrated salt be incorrect?

Answer 6

Not all of the mass of water is removed
The salt may have decomposed

Question 7

Formula link V, N , and C

Answer 7

N=cV

Question 8

What is the molar gas volume?

Answer 8

The volume per mole of gas molecules at a stated temperature and pressure (at RTP 24dm3)

Question 9

What are the conditions are RTP?

Answer 9

298K
100KPa

Question 10

What is the ideal gas equation?

Answer 10

pV=nKt

Pressure (pa) x Volume (m3)= Moles x Gas constant x Temperature (Kelvin)

Gas Constant = 8.314
+273 to convert celcius to Kelvin

Question 11

What is Stoichiometry?

Answer 11

The ratio of the amount, in moles, of each substance in a chemical reaction

Question 12

What is the formula for percentage yield?

Answer 12

(Actual Yield/ Theoretical Yield ) x 100

Question 13

What is the formula for atom economy ?

Answer 13

(Mr of desired product/ Mr total products) x 100

Question 14

What would happen to the water of crystallisation coefficient if not all of the water was removed in the experiment?

Answer 14

Too small
Not all of the water is removed so it would appear to be smaller than it is

Question 15

What would happen to the coefficient of the crystallisation of water in the experiment if some of the salt decomposed?

Answer 15

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

Question 16

How can you improve the accuracy of heating to collect gas in a gas syringe?

Answer 16

Heat until the volume does not change
Wait for the syringe to cool before measuring volume

Question 17

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?

Answer 17

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

Question 18

How can you decrease the percentage uncertainty of the heating till constant mass experiment?
How do you measure percentage uncertainty for this experiment?

Answer 18

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