yr1 calculations

The mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12.

Relative atomic mass is the average mass of one atom compared to one-twelfth of the mass of one atom of carbon-12

Relative molecular mass is the average mass of a molecule compared to one-twelfth of the mass of one atom of carbon-12

There are 6.022 x 1023 atoms in 12 grams of carbon-12. Therefore explained in simpler terms ‘One mole of any specified entity contains 6.022 x 1023 of that entity’:

No of particles = moles of substance (in mol) X Avogadro’s constant

moles = mass/Ar = 6.00/ 118.7 = 0.05055 mol Number atoms = moles x 6.022 x 1023 = 0.05055 x 6.022 x 1023 = 3.04 x1022

mass over volume

An empirical formula is the simplest ratio of atoms of each element in the compound

: A molecular formula is the actual number of atoms of each element in the compound

C3H6O has a mass of 58 The empirical formula fits twice into Mr of 116 So molecular formula is C6H12O2

A Hydrated salt contains water of crystallisation

x=10 Molar mass xH2O = 322.1 – (23x2 + 32.1 + 16x4) = 180 X = 180/18 =10

• Weigh an empty clean dry crucible and lid. • Add 2g of hydrated calcium sulfate to the crucible and weigh again • Heat strongly with a Bunsen for a couple of minutes • Allow to cool • Weigh the crucible and contents again • Heat crucible again and reweigh until you reach a constant mass ( do this to ensure the reaction is complete).

The lid improves the accuracy of the experiment as it prevents loss of solid from the crucible but should be loose fitting to allow gas to escape

• Weigh the sample bottle containing the required mass of solid on a 2 dp balance • Transfer to the beaker and reweigh sample bottle • Record the difference in mass • Add 100cm3 of distilled water to the beaker. Use a glass rod to stir to help dissolve the solid. • Sometimes the substance may not dissolve well in cold water so the beaker and its contents could be heated gently until all the solid had dissolved. • Pour the solution into a 250cm3 graduated flask via a funnel. • Rinse beaker and funnel and add washings from the beaker and glass rod to the volumetric flask. • make up to the mark with distilled water using a dropping pipette for the last few drops. • Invert flask several times to ensure a uniform solution. Remember to fill so the bottom of the meniscus sits on the line on the neck of the flask. With dark liquids like potassium manganate, it can be difficult to see the meniscus

• Pipette 25cm3 of original solution into a 250cm3 volumetric flask • make up to the mark with distilled water using a dropping pipette for the last few drops. • Invert flask several times to ensure a uniform solution. Using a volumetric pipette is more accurate than a measuring cylinder because it has a smaller uncertainty Use a teat pipette to make up to the mark in a volumetric flask to ensure the volume of solution accurately measured and one doesn’t go over the line.

new diluted concentration = original concentration x original volume over new diluted volume