Question

The human population is increasing, so more food needs to be produced. Farmers use fertilisers to increase the yield of wheat. A farmer wants to find out the optimum concentration of fertiliser to use on his wheat plants. He has a stock solution of concentrated fertiliser which is stated as 100%. He dilutes the stock solution to make 5%, 10%, 15%, and 20% solutions. He makes 100 cm³ of each solution.

Describe how the farmer prepares 100 cm³ of the 20% solution?

a) Measure 20 cm³ of the concentrated 100% fertiliser and add it to 80 cm³ of water.
b) Measure 20 cm³ of water and add it to 80 cm³ of the concentrated 100% fertiliser.
c) Mix equal parts of the concentrated 100% fertiliser and water, each measuring 50 cm³.
d) Dilute 20 cm³ of the concentrated 100% fertiliser with 80 cm³ of the 5% solution.

Answer 1

To prepare 100 cm³ of a 20% fertiliser solution, the farmer should measure 20 cm³ of the 100% stock solution and mix it with 80 cm³ of water.

Step-by-step explanation:

The farmer prepares 100 cm³ of the 20% solution by measuring 20 cm³ of the concentrated 100% fertiliser and adding it to 80 cm³ of water. This is because when preparing a solution of a desired concentration, it is necessary to dilute a small volume of a more concentrated solution with additional solvent. In this case, the concentrated fertiliser is the stock solution, and by adding water to it in a specific ratio, the farmer can achieve the desired concentration.

The preparation of a 20% solution from a concentrated stock solution of fertiliser involves adding a certain volume of the stock solution to a certain volume of water to achieve the desired concentration. The correct method to prepare 100 cm³ of a 20% solution would be to measure 20 cm³ of the concentrated 100% fertiliser and add it to 80 cm³ of water, as in option a). This maintains the total volume at 100 cm³ while ensuring the final concentration is 20% of the original.