Final answer:
To prepare a 20% zinc oxide ointment from a 5% zinc oxide ointment, 600g of zinc oxide should be added to the existing 3200g of ointment.
Step-by-step explanation:
To prepare an ointment containing 20% zinc oxide from a 5% zinc oxide ointment, we need to calculate the additional amount of zinc oxide required. The starting mass of the ointment is 3200g, and it contains 5% zinc oxide, which is 160g of zinc oxide (5% of 3200g). To have a 20% zinc oxide ointment, we need to have 20% of the final mass of the ointment as zinc oxide.
Let's denote the additional amount of zinc oxide required as x. The final amount of zinc oxide will be 160g + x, and the final mass of the ointment will be 3200g + x.
In equation form: 0.20 × (3200g + x) = 160g + x.
Solving for x gives us:
- 640g + 0.20x = 160g + x
- 0.20x - x = 160g - 640g
- -0.80x = -480g
- x = 600g
Therefore, 600g of zinc oxide should be added to the ointment to achieve the desired concentration.