RP1a: Making a standard solution

What is the first step in making a standard solution? (1)

Weigh the sample bottle containing the required mass of solid on a 2 decimal place balance

How is the mass of the solid determined after transferring it to the beaker? (1)

Reweigh the sample bottle and record the difference in mass (differential weighing)

How is the solid dissolved in the beaker? (2)

1. Add 100 cm³ of distilled water to the beaker.

2. Use a glass rod to stir and help dissolve the solid.

How is the solution transferred to the volumetric flask? (2)

1. Pour the solution into a 250 cm³ graduated flask via a funnel.

2. Rinse the beaker and funnel, adding the washings to the volumetric flask.

How is the solution made up to the required volume? (2)

1. Add distilled water up to the mark using a dropping pipette for the final few drops.

2. Invert the flask several times to ensure a uniform solution.

What should be done if the substance does not dissolve in cold water? (1)

The beaker and its contents should be gently heated until all the solid has dissolved

Why is it important to correctly fill the volumetric flask up to the mark? (1)

- The bottom of the meniscus must sit on the line to ensure accurate concentration

- Especially for dark liquids like potassium manganate, where the meniscus is hard to see