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Pharmacy maths calculations, please help and show workings!

1. How many millimol of sodium chloride are contained in 250 mL of a 0.9% saline solution? [atomic]

38.5 mmol

2. What volume of a 2% solution can be produced from 300 mL of 250 mg/10 mL solution?
375 mL

3. An infusion solution contains 100 mg phenylephrine in 500 mL. What rate of infusion should be used to give 130 mcg/min when using a giving set delivering 20 drops/mL?

13 drops per minute

4. How much benzalkonium chloride (in mg) is required to make 60 mL of a solution which, when 15 mL is diluted to 150 mL, produces a 1 in 1250 solution?

480 mg

5. . How manygrams of potassium chloride are needed to prepare 500 mL of a solutioncontaining 6 mmol of potassium ions per 5 mL spoonful?

[Atomicweight]

44.7 g

I don't know how to get the answers :frown:

(edited 8 years ago)

Reply 1

ghostwalker

Original post by yellow333

1. How many millimol of sodium chloride are contained in 250 mL of a 0.9% saline solution? [atomic]

38.5 mmol

I'll do the first one for you, but you then need to have a go at the rest yourself.

0.9% w/v means 0.9g in 100ml

Multiply by 2.5 to get 2.25g in 250ml.

mol. wt. NaCl is 23+35.5 = 58.5g

So, 1 mole of NaCl weight 58.5g

Divide by 58.5 and multiply by 2.25:

2.25/58.5 moles weigh (58.5/58.5)x2.25=2.25g.

And 2.25/58.5 = 0.03846... moles

= 38.5 mmol

(edited 8 years ago)