1. ALLIGATIONS

2. Purpose
Used when you need to prepare (compound) a percent strength that you do not have in stock.
To make the strength you need to use TWO other strengths to attain the correct one.

3. EXAMPLE
If a doctor orders 20% KCL, but you only have 10% and 50% on hand, you would have to calculate the amount of each solution to attain a 20% solution.
You can only do this if at least one of the two strengths is less concentrated than the final solution.
This means that you cannot make a 20% solution from a 5% and a 10% solution.
Water can be used as another element for a solution and water is considered 0%.

4. PROBLEM
You have in stock 70% solution and a 20% solution. How much of each do you need in order to create 1L of 40% solution?
We will work it together coming up…. Please have a scrap piece of paper available.

5. Use a simple TIC-TAC-TOE diagram following these rules:
Draw a tic-tac-toe board.
Place your desired strength in the middle square.
40%

6. Use a simple TIC-TAC-TOE diagram following these rules:
Put your higher strength solution in the top left square. 20
Put your lower strength in the bottom left square. If you are using water, you will place a zero in this square.

7. Tic-tac-toe diagram (Continued)
Subtract the lower number (top left or middle) from the lower number (top left or middle) and put that # in the bottom right square. Then do the same with the middle and bottom left squares and place that # in the top right square.
Then add the right top and bottom numbers. Divide the top right by this new #. Then, divide the bottom right by this new number.
.20 / .50 = .40 and .30/.50 = .60

8. Tic-tac-toe diagram (Continued)
Multiply both numbers (individually) by the total volume that you need. This will be how much you will need of each solution.
.40 X 1000ml (1 L) = and .60 X 1000ml = 600
Check your answer by adding the two parts. They should equal the total volume.
= 1000ml (1 L)

9. Practice problem
Prepare a 20% KCL 500ml from your stock of 5% and 70% KCL. Answer: 70% = 115ml 5% = 385ml