# AS Chemistry (NEW-2008) : Calculations

Calculations Formalae

HideShow resource information

First 295 words of the document:

Chemistry HELP-SHEET 4
MOLE CALCULATIONS
· the mole is the standard unit of amount ... its value is 6.022 x 1023
· molar mass = the mass of one mole ... it is usually measured in grams per mol... g mol-1
· to calculate the number of moles ... use one of the following relationships
SINGLE SUBSTANCE MOLES = MASS / MOLAR MASS
mass = moles x molar mass
molar mass = mass / moles
SOLUTION moles = concentration x volume
concentration = moles / volume
volume = moles / concentration
BUT if volume is in cm3 MOLES = CONCENTRATION x VOLUME (in cm3)
1000
EQUATIONS · give you the ratio in which chemicals react and are formed
· need to be balanced in order to do a calculation
WORKED EXAMPLE
CaCO3 + 2HCl ------> CaCl2 + CO2 + H2O
1. What is the relative molecular mass of CaCO3 ? ANS 40 + 12 + (3 x 16) = 100
2. What is the mass of 1 mole of CaCO3 ? ANS 100 g
3. What does 0.1M HCl mean ? ANS the concentration is 0.1 mol dm-3
4. How many moles of HCl are in 20cm3 of 0.1M HCl ? ANS 0.1 x 20 = 0.002 moles
1000
5. How many moles of CaCO3 will react ? ANS ½ x 0.002 = 0.001 moles
6. What is the mass of 0.001 moles of CaCO3 ? ANS mass = moles x molar mass
= 0.001 x 100 = 0.1 g
7. What mass of CO2 is produced ? ANS moles of CO2 = moles of CaCO3
moles of CO2 = 0.001 moles
mass of CO2 = 0.001 x 44 = 0.044g
QUESTION
a) Balance the equation :- NaOH + H2SO4 ------> Na2SO4 + H2O
b) How many moles in 30 cm3 of 0.100M H2SO4 ?
c) How many moles of NaOH will react with 30 cm3 of 0.100M H2SO4 ?
d) What volume of 0.08M NaOH will react with 30 cm3 of 0.100M H2SO4 ?