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# Help!!! watch

1. an someone please show me how to work these out?!!!!

How much solid must be used to make up 2 litres of a 0.3% weight/volume solution?

How much solid must be used to make up 360ml of a 1 in 10 solution?

How much salbutamol syrup (2mg/5ml) is required to make up 100ml of salbutanol syrup containing 1.5mg/5ml?

What volume of 90% alcohol is required to prepare 450ml of 60% alcohol?

How much pholcodiene linchus 5mg/5ml is required to make 400ml of paedratic pholcodiene linchus 2mg/5ml?
2. (Original post by kay123)
an someone please show me how to work these out?!!!!

How much solid must be used to make up 2 litres of a 0.3% weight/volume solution?
How much solid must be used to make up 360ml of a 1 in 10 solution?
How much salbutamol syrup (2mg/5ml) is required to make up 100ml of salbutanol syrup containing 1.5mg/5ml?
What volume of 90% alcohol is required to prepare 450ml of 60% alcohol?
How much pholcodiene linchus 5mg/5ml is required to make 400ml of paedratic pholcodiene linchus 2mg/5ml?
1. w/v is mass of solute and volume of solvent - 2000cm3 water with 6g of solute dissolved

2. 1 in 10 means 10% so 36g solute made up to 360ml with solvent

3. In this case the volume of the syrup must be taken into account
100ml of the target syrup must contain 1.5 x 20 mg = 30mg
to get this mass you must use 6 x 5ml of the source syrup = 30ml
the total volume = 100ml so you make up 30ml of source syrup + 70ml of solvent.

4. The quantity of alcohol in 450ml of 60% = 450 x 0.6 = 270 parts alcohol
in the source solution there are 0.9 parts alcohol therefore you need 270/0.9 ml to obtain the requirement = 300ml then add 150ml of solvent

5. Again target requirement = 400ml at 2mg/5ml
400/5 = 80 therefore mass required = 80 x 2 = 160mg
to obtain 160 mg from the source solution you need 160/5 lots of 5 ml = 160ml
So your solution is made by combining 160ml of the source soluton with 240 ml of the solvent.

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Updated: June 19, 2005
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