Preparing a Solution

What is the mass of K₂CO₃ solid needed to prepare 250.0 cm³ 0.500 M solution?

(R.a.m. : K = 39.1, C = 12.0, O = 16.0)

• 138.20 g

• 34.55 g

• 17.28 g

• 8.64 g

What are the correct steps in preparing a standard solution of 250.0 cm³ of ethanedioic acid solution from its solid? (use the number in correct order)

(1) Add distilled water until the bottom of meniscus reaches the graduation mark.

(2) Dissolve the weighed solids in a beaker using about 100 cm³ of distilled water.

(3) Stopper the flask and invert the flask several times to mix the contents well.

(4) Weigh a calculated mass of ethanedioic acid solid.

(5) Wash the beaker and the glass rod with distilled water several times and pour all the washings into the flask.

(6) Add distilled water into the flask until the meniscus of solution if about 2 cm below the graduation mark.

• 4, 5, 2, 6, 1, 3

• 4, 2, 5, 6, 1, 3

• 4, 1, 5, 2, 6, 3

• 4, 2, 6, 5, 1, 3

Which of the following equipment is used for diluting a 0.500 M NaOH solution to 0.0500 M?

• Measuring cylinder, glass rod, volumetric flask, beaker

• Pipette, volumetric flask, pipette filler

• Pipette filler, pipette, volumetric flask, dropper

• Dropper, volumetric flask, measuring cylinder

Which of the following chemicals CANNOT be used for preparing a standard solution directly from its solid?

• K₂CO₃

• Ethanedioic acid

• Na₂CO₃

• NaOH

Which of the following is NOT the criteria for using as a primary standard?

• Pure

• Stable

• Soluble in water

• Colour