RP1 - Make up a Volumetric Solution

Question 1

Making a volumetric solution of 250cm3 solution of Sodium Hydrogen Carbonate With a concentration of 0.100Mol dm3

Question 2

Describe how you would carry out a volumetric solution?

Answer 2

1. Place a clean, dry weighing boat on a mass balance and zero
2. Take the empty weighing boat off the balance and add using a spatula approx. the correct mass of Sodium Hydrogen Carbonate
3. Re weigh and repeat step 3 adding small amount of the solid, until the required mass = obtained
4. Carefully without spilling any solid, place all in clean 250cm^3 beaker and add about 100cm^3 of water. Rince the weighing boat several times to ensure all crystals have been transferred in to the beaker (known as the washings.
5. Do not add more than 200cm^3 at this stage
6. Stir and crush crystals if needed until all the solid has dissolved
7. Pour solution using a clean funnel into a clean 250cm^3 volumetric flask
8. Use wash bottle to rinse the beaker and funnel in to the volumetric flask. Rinse the stirring rod in to these washings
9. use pastette to add water carefully dropwise until bottom of miniscus sits on the 250cm^3 line.
10. Place a stopper on the volumetric flask and invert/shake thoroughly

Question 3

What are some errors that we need to make sure of in this investigation?

Answer 3

● If using anhydrous sodium hydrogensulfate (NaHSO4 ), make sure it is not too old as it will have picked up water and therefore mass values will not be as accurate.
● Balance – usually gives to 0.01g (systematic error - same for each value that is recorded).
● Alternatively the known mass of solid in the weighing bottle could be transferred to beaker, washed and washings added to the beaker.
● Remember to fill so the bottom of the meniscus sits on the line on the neck of the flask. With dark liquids like potassium manganate (K2MnO4) it can be difficult to see the meniscus, so placing a piece of white paper behind to make the marker clearer to see.

Question 4

How do we reduce uncertainties in measuring mass?

Answer 4

● Using a more accurate balance or a larger mass will reduce the uncertainty in weighing a solid.
● Weighing sample before and after addition and then calculating difference (weighing by difference) will ensure a more accurate measurement of the mass added.

Question 5

Finish