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Amounts of Substance

Key formulas

Mass= Relative Molecular mass x Moles
Pressure x Temperature=number of moles x Gas Constant x Volume
Percentage yield= Actual yield/Theoretical yield x 100
% Atom economy= Mass of desired product/Total mass of reactants x 100

How to convert between dm3, cm3 and m3

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Doing a titration

First wash out a conical flask with distilled water and a pipette with the alkali that you are
using. This prevents cross contamination.
Then measure out some alkali using a pipette and put it in a conical flask along with some
indicator. Either Methyl Orange or Phenolphthalein…

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Question based on titrations and using formulas

MgCO3+2HCl MgCl2 +H2O +CO2

When 75.0 cm3 of 0.500 moldm-3hydrochloric acid were added to 1.25g of impure MgCO3 some
acid was left unreacted. This unreacted acid required 21.6cm3 of a 0.500 moldm-3 solution of
sodium hydroxide for a complete reaction.

(i)Calculate the number…

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Mass= Mr Moles

Moles= Mass/Mr

1.00g/101.1 =? = 9.89x10-3

Question using Ideal Gas Equation

(ii)At 298 K and 100kPa the oxygen gas produced in this decomposition occupied a volume of
1.22 x 10-4 m3.

State the ideal gas equation and use it to calculate the number of moles of oxygen…

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1K 2K 1K 2K

1N 2N 1N 2N

3O 6O 4O 6O

2KNO3 2KNO2 + O2

Question on atom economy and % yield.

Cr2O3 + 2Al ---> 2Cr + Al2O3
(i)Calculate % atom economy for Chromium

Mass of desired product/Total mass of reactants x 100

2(52)/(52+52)+(16+16+16)+2(27) =0.5048543689



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