What is the concentration of the sucrose in the last tube En

What is the concentration of the sucrose in the last tube? Enter the answer in the text box (round up to nearest hundredth, if needed; e.g., 12.88) %

Solution

concentration of sucrose in the last test tube is 6.07%

Clearly, all of the sucrose that there will be in the first dilution solution must come from the 2mL of the 95% (w/v) sucrose solution that you add to the 10mL of water. (The 10 mL of water, itself, contains no sucrose.) Therefore, the total mass of sucrose in the first dilution solution must be 2mL X 0.95g/mL = 1.90 g. Note that in the original sucrose solution 95% (w/v) means 95g sucrose per 100 mL of solution, which is also 0.95 g/mL. Multiplying that gives you 1.90g of sucrose. Again, that is the total amount (mass, weight) of sucrose that the first (diluted) solution will contain.

When you multiplied 2mL by 0.95 g/mL, the mL units canceled out

At this point in working the problem, you have 1.90 g of sucrose. Obviously, that is not a concentration expression. Continuing, that 1.90 g of sucrose is now in a total volume (firs dilution solution) of 2mL + 10 mL = 12mL. Therefore, the concentration of the new solution is 1.90g/12mL = 0.158g/mL, which is the same as 15. 8g/100 mL, which is 15.8% (w/v)

From this first dilution solution (Second test tube) we added 5ml into 8ml of water. 0.158g/mL*5mL=0.79g

0.79g of sucrose is now in a total volume (Second dilution solution) of 5mL +8mL=13mL.Therefore the concentration of final solution is 0.79g/mL/13mL=0.0607/mL, 6.07g/100mL, which is 6.07%(w/v).