• The?concentration?of a solution is the amount of?solute?dissolved in a?solvent?to make 1 dm3?of??solution
  • The solute is the substance that dissolves in a solvent to form a solution
  • The solvent is often water

   

• A?concentrated?solution is a solution that has a?high?concentration of solute
• A?dilute?solution is a solution with a?low?concentration of solute
• When carrying out calculations involve concentrations in mol dm-3?the following points need to be considered:
  • Change mass in grams to?moles
  • Change cm3?to dm3

   

• To calculate the?mass?of a substance present in solution of known?concentration and volume:
  • Rearrange the concentration equation

   

number of moles (mol) = concentration (mol dm-3) x volume (dm3)

• • Multiply the moles of solute by its molar mass

mass of solute (g) = number of moles (mol) x molar mass (g mol-1)

Answer

Step 1:?Write the balanced symbol equation

CaCO3??+ ?2HCl ?→ ?CaCl2??+ ?H2O ?+ ?CO2

Step 2:?Calculate the amount, in moles, of calcium carbonate that reacts

Step 3:?Calculate the moles of hydrochloric acid required using the reaction’s stoichiometry

1 mol of CaCO3?requires 2 mol of HCl

So 0.025 mol of CaCO3?requires 0.05 mol of HCl

Step 4:?Calculate the volume of HCl required

Volume of hydrochloric acid = 0.05 dm3

Answer

Step 1:?Write the balanced symbol equation

Na2CO3??+ ?2HCl ?→? 2NaCl ?+ ?H2O ?+ ?CO2

Step 2:?Calculate the amount, in moles, of sodium carbonate reacted by rearranging the equation for amount of substance (mol) and dividing the volume by 1000 to convert cm3?to dm3

amount (Na2CO3) = 0.025 dm3?x 0.050 mol dm-3?= 0.00125 mol

Step 3:?Calculate the moles of hydrochloric acid required using the reaction’s stoichiometry

1 mol of Na2CO3?reacts with 2 mol of HCl, so the molar ratio is 1 : 2

Therefore 0.00125 moles of Na2CO3?react with 0.00250 moles of HCl

Step 4:?Calculate the concentration, in mol dm-3, of hydrochloric acid

concentration (HCl) (mol dm-3) = 0.125 mol dm-3

Volumes of gases

• Avogadro?suggested that ‘equal volumes of gases contain the same number of molecules’ (also called?Avogadro’s hypothesis)
• At room temperature (20 degrees Celsius) and pressure (1 atm)?one mole?of any gas has a volume of 24.0 dm3
• This?molar gas volume?of 24.0 dm3?mol-1?can be used??to find:
  • The volume of a given mass or number of moles of gas:

   

volume of gas (dm3) = amount of gas (mol) x 24?dm3?mol-1

• The mass or number of moles of a given volume of gas:

Answer