Specification Point 1.34C (Paper 2C Only):
Understand how to carry out calculations involving Amount of Substance, Volume and Concentration (in mol / dm3 ) of Solution
Amount of Substance (mol) = Concentration x Volume of Solution (dm3)
Calculate the Moles of Solute Dissolved in 2 dm3 of a 0.1 mol / dm3 Solution
Concentration of Solution : 0.1 mol / dm3
Volume of Solution : 2 dm3
Moles of Solute = 0.1 x 2 = 0.2
Amount of Solute = 0.2 mol
25.0 cm3 of 0.050 mol / dm3 sodium carbonate was completely neutralised by 20.00 cm3 of dilute hydrochloric acid. Calculate the concentration, in mol / dm3 of the hydrochloric acid.
Step 1 – Calculate the amount, in moles, of sodium carbonate reacted
Amount of Na2CO3 = ( 5.0 x 0.050 ) ÷ 1000 = 0.00125 mol
Step 2 – Calculate the amount, in moles, of hydrochloric acid reacted
Na2CO3 + 2HCl → 2NaCl + H2O + CO2
1 mol of Na2CO3 reacts with 2 mol of HCl
0.00125 mol of Na2CO3 Reacts with 0.00250 mol of HCl
Step 3 – Calculate the concentration, in mol / dm3, of the Hydrochloric Acid
1 dm3 = 1000 cm3
Concentration ( mol / dm3 ) = 0.00250 ÷ ( 20 ÷ 1000 ) = 0.125
Concentration of Hydrochloric Acid = 0.125 mol / dm3
Calculate the volume of hydrochloric acid of concentration 1.0 mol / dm3 that is required to react completely with 2.5g of calcium carbonate.
Step 1 – Calculate the amount, in moles, of calcium carbonate that reacts
Mr of CaCO3 is 100
Amount of CaCO3 = ( 2.5 ÷ 100 ) = 0.025 mol
Step 2 – Calculate the moles of hydrochloric acid required
CaCO3 + 2HCl → CaCl2 + H2O + CO2
1 mol of CaCO3 requires 2 mol of HCl
0.025 mol of CaCO3 Requires 0.05 mol of HCl
Step 3 – Calculate the volume of HCl Required
Volume = ( mol of Substance ÷ Concentration )
= 0.05 ÷ 1.0
= 0.05 mol
Volume of Hydrochloric Acid = 0.05 mol
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Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.
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