QUESTION 1
How much 50% glucose contains the same amount of glucose as 500 ml of 17.5% glucose?
- 17.5% w/v glucose = 17.5 g/100 ml = 87.5 g/500 ml
- 50% glucose = 50 g/100 ml
- 87.5 g / 50 g = 1.75 dl (175 ml)
QUESTION 2
If you use your answer to Question 1 to make up 500 ml of your final solution, but using 10% glucose as a diluent rather than water, what will the final glucose concentration be?
- 175 ml of the solution will be 50% glucose, which will provide 87.5 g of glucose
- To make up to 500 ml, we will need 500 – 175 = 325 ml of 10% glucose
- 10% glucose = 10 g/100 ml; therefore, 32.5 g/325 ml
- This means the total amount of glucose is 32.5g + 87.5 g = 120 g
- 120 g in 500 ml = 24 g/100 ml = 24%w/v
QUESTION 3
Substitute the appropriate values into the equation above to produce a ratio of the concentrations required.
- High-concentration solution (50%) ratio = 17.5 - 10 = 7.5
- Low-concentration solution (10%) ratio = 50 - 17.5 = 32.5
- Therefore, to make an appropriate solution for every 7.5 parts of 50% glucose needed, we need to dilute it with 32.5 parts of 10% glucose. As a quick internal sense check, the less concentrated solution is in the greater quantity, so the answer looks initially reasonable.
QUESTION 4
Use the ratios from Question 3 to calculate the volumes of each solution required to make 500 ml of 17.5% weight per volume (w/v) glucose.
- From Q3, we can see that the total number of parts is 7.5 + 32.5 = 40 parts
- 500 ml divided by 40 parts = 12.5 ml per part
- For 10% glucose, we need 12.5 ml x 32.5 parts = 406.25 ml
- For 50% glucose, we need 12.5ml x 7.5 parts = 93.75 ml
QUESTION 5
Using your calculated answers from Question 4, check your answer is correct by calculating the amounts of glucose present in the initial solutions and totalling them together for the amount in the final solution. Does this provide 17.5 g/100 ml?
- 10% glucose = 10g in 100ml; in 406.25ml, there will be 40.625g glucose
- 50% glucose = 50g in 100ml; in 93.75ml, there will be 46.875g glucose
- Total amount of glucose in the final solution = 40.625g + 45.875g = 87.5g
- Volume of final solution = 406.25ml + 93.75ml = 500ml
- Final concentration = 87.5g/500ml = 17.5g/100ml = 17.5%w/v