What is a standard solution?
A standard solution is one of known concentration. Its concentration is usually given in mol/dm3.
Standard solution preparation
Standard solutions can be prepared in TWO ways:
(i) By dissolving an accurately measured mass of solute in a known volume of solvent, or
(ii) By diluting a more concentrated solution
(i) By dissolving an accurately measured mass of solute in a known volume of solvent, or
(ii) By diluting a more concentrated solution
Making up the standard solution using a measured mass:
1. Take a watch glass and place it on the balance. Tare the balance (set it to zero). Carefully weigh out the required mass of substance.
2. Transfer this amount to a beaker. Add water from a wash bottle to dissolve it. Use some of the water to rinse all the substance off the watch glass. Do this at least twice.
3. Stir with a glass rod until all the solid is dissolved, then transfer the solution to the volumetric flask. Use more water from the wash bottle to rinse out the beaker and the glass rod.
4. Add water to just below the line on the volumetric flask. Add the final drops with a dropper to ensure that the bottom of the meniscus is on the line.
5. Put the lid on the flask and turn the flask over a couple of times to mix the solutions.
6. Label your solution.
2. Transfer this amount to a beaker. Add water from a wash bottle to dissolve it. Use some of the water to rinse all the substance off the watch glass. Do this at least twice.
3. Stir with a glass rod until all the solid is dissolved, then transfer the solution to the volumetric flask. Use more water from the wash bottle to rinse out the beaker and the glass rod.
4. Add water to just below the line on the volumetric flask. Add the final drops with a dropper to ensure that the bottom of the meniscus is on the line.
5. Put the lid on the flask and turn the flask over a couple of times to mix the solutions.
6. Label your solution.
Problem: How much sodium chloride is needed to make 1 litre of an aqueous 1M solutions?
Answer:
1) Calculate the molar mass of NaCl.
Molar mass of NaCl: Na (23) + Cl (35.5)= 58.5g/mol
2) To make a 1M solution of NaCl, dissolve 58.5 grams of the salt in some distilled water (add enough water to dissolve the salt). 3) Then add more water to the flask until it totals 1 litre.
End result: 1M NaCl solution.
1) Calculate the molar mass of NaCl.
Molar mass of NaCl: Na (23) + Cl (35.5)= 58.5g/mol
2) To make a 1M solution of NaCl, dissolve 58.5 grams of the salt in some distilled water (add enough water to dissolve the salt). 3) Then add more water to the flask until it totals 1 litre.
End result: 1M NaCl solution.
Making molar solutions from concentrated aqueous solutions
Problem: Make 1 litre of a 1M aqueous solution of sulphuric acid.
Answer:
1) Read the label on the sulphuric acid reagent bottle. The label will tell you the molarity (which is usually 18.0 M). This means that there are 18.0 moles of sulphuric acid in each litre of solution.
2) To make a much more diluted solution, you will need to add one mole of the concentrated acid to a fresh batch of water. HOW DO WE DO THIS?
3) If 18 moles of sulphuric acid is contained in 1000ml,
Then 1 mole of sulphuric acid will be contained in 1 mole x 1000ml / 18 moles
Therefore, the volume of acid needed is 55.6ml
SO, we add slowly 55.6mls of the acid to 500ml distilled water. The flask is then filled with more water to "top it off" to the 1 litre mark on the flask.
The end result a 1M sulphuric acid solution.
NB: NEVER add water into a large volume of concentrated acid. You risk creating an explosion.
Answer:
1) Read the label on the sulphuric acid reagent bottle. The label will tell you the molarity (which is usually 18.0 M). This means that there are 18.0 moles of sulphuric acid in each litre of solution.
2) To make a much more diluted solution, you will need to add one mole of the concentrated acid to a fresh batch of water. HOW DO WE DO THIS?
3) If 18 moles of sulphuric acid is contained in 1000ml,
Then 1 mole of sulphuric acid will be contained in 1 mole x 1000ml / 18 moles
Therefore, the volume of acid needed is 55.6ml
SO, we add slowly 55.6mls of the acid to 500ml distilled water. The flask is then filled with more water to "top it off" to the 1 litre mark on the flask.
The end result a 1M sulphuric acid solution.
NB: NEVER add water into a large volume of concentrated acid. You risk creating an explosion.