How do I go about doing this in a lab?

Question

Solution preparation

1. Prepare 20 mls of a 10% w/v solution of cobaltous chloride (pink colour, max. ABS @510nm)

in a 30ml sample bottle.

2. Using pipettes and sample bottles, make dilutions of the 10% stock to give 8%, 4%, 2%, 1%

and 0.5% solutions (all w/v); each 10mls volume.

Answer 1

1). To make the original stock 10% (w/v) cobaltous chloride (CoCl₂):

10% (w/v) = 10 g Co Cl₂ / 100 ml

To make 20 mls: 10 g/100 ml x 20 ml = 2 g

Weigh 2 g CoCl₂ and place it in the 30 ml sample bottle.

Add 20 mls of water (use a 20 ml pipet if available)

2). To make the desired dilutions you can use C1V1 = C2V2 where C1 = initial concentration (10%), V1 = volume of that (?), C2 = final concentration (8%, 4%, 2%...) and V2 = final volume (10 ml)

8%: (x ml)(10%) = (10 ml (8%); x = 8 mls. Take 8 mls original stock and add 2 mls water

4%: (x ml)(10%) = (10 ml)(4%); x = 4 mls. Take 4 mls original stock and add 6 mls water

etc....etc...

Hopefully you see the trend and can do the others yourself.