Preparing Standard Solutions From Solids From Liquids

What is a standard solution? A standard solution is a solution whose concentration is known accurately. Its concentration is usually given in mol/L. When making up a standard solution it is important that the correct mass of substance is accurately measured. It is also important that all of this is successfully transferred to the volumetric flask used to make up the solution.

Standard solution from Solid 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 the appropriate sized volumetric flask. Be careful to transfer all of the solid

3. Add enough distilled water to half-fill the volumetric flask 3. Add enough distilled water to half-fill the volumetric flask. Swirl to dissolve the crystals. 4. Add distilled water to just below the line on the volumetric flask. Add the final drops carefully 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 solution. 6. Label your solution with your name, the date, and the contents, e.g. 2.0M NaCl. Then tidy up!

Standard Solution from Liquid This can also be referred to as a dilution. A small volume of a solution of known concentration is used to make a diluted solution. The new concentration can be calculated using the equation below.             c1v1=c2v2          First, an exact volume of a solution of known concentration is pipetted into a clean volumetric flask. Second, the solution is diluted to the volumetric mark using distilled water.

Concentration Units % by mass - medicated creams % by volume - rubbing alcohol ppm, ppb - water contaminants molarity - used by chemists molality - used by chemists

PPM, PPB Parts per million is a unit used for VERY LOW concentrations of solute

Example Find the concentration of a 3.5 mL sample if 3.0 x 10-6 g of a toxin is found in the sample.

Calculating Solute needed for Standard Solutions Calculate the mass of Zn(NO3)2 needed to make up 250.0 mL of 1.5 M solution

Calculating Dilution What volume of 18M H2SO4 is needed to prepare 500.0 mL of 2.5M H2SO4?