Question

You have made the following coal tar ointment Coal tar 4 g Castor oil 2 g Emulsifying ointment 94 g The current prescription requires an ointment with 2.0 % w/w coal tar. How many g of emulsifying ointment would need to be added to 230 g of the coal tar ointment above to make an ointment with 2.0 % w/w coal tar? (1 decimal places)

Answer 1

Coal tar 4gm

Castor oil 2gm

Emulsifying ointment 94gm

Total gm of coal tar ointment - 100gm

To calculate how many g of emulsifying ointment would need to be added to 230 g of the coal tar ointment above to make an ointment with 2.0 % w/w coal tar

Using unitary method :

100gm of coal tar contains 94gm of emulsifying ointment

1gm of coal tar will contain 94/100gm of emulsifying ointment

Then 230gm of coal tar ointment will have 94/100×230

= 216.2 gm of emulsifying ointment