APhA Naplex Quizbank - Calculation question

[yummygummy]

Hi SDN,

Could someone please explain the following calculation problem to me --
Calculate the amount of water (in grams) in 100 mL of 65% (w/w) syrup that has a density of 1.313.

Answer: 45.95 g

APhA explanation:
Note that 65 %w/w means 65 g in 100 g syrup. The total weight of the 100 mL syrup is 100 mL x1.313 (density) = 131.3 g. Every 100 g of syrup contains 35 g of water, so...[explanation is cut off in my google chrome and safari browser]

My work:
65% = 65grams solute/100 grams syrup
65grams solute/1.313 = 49.5 mg displaced by solute
100mL total volume - 49.5 mg volume displaced = 50.5mg water

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[yummygummy]

I've already done the RxPrep calculations and the SDN 120 calculations. I'm doing the Apha quizbank with math calculations for more practice and find some unfamiliar questions such: aliquots, ppm, ppb, dissociation factor, minimum weighable quantity, freezing point depression, etc. Have any of you seen these types of question on the Naplex thus far? Thank you!

 

[rxbud]

Hi,I did this way Bro.
step 1: 65 remaining from 100 syrup is 35
Step 2: 35*100/100ml=35
step 3: 35*1.313=45.955 gm, so lets round it to nearest 100th for answer so its 45.95gm.
Hope this help you.

 

[NAPLEXCPJE2014]

rxbud's explaination is correct. But I doubt, whether we can multiply 35 (which is already in grams) by 1.313 (which is density) to get the weight of water again in grams.

To continue with AphA explanation:
100 gms contain 65 gms of syrup and 35 gms of water
Weight of 100 ml syrup is 100 * 1.313 (density) = 131.3 gms
Now, 100 gms syrup contain 35 gms of water. 131.3 gms of syrup contain how many gms of water?
131.3 * 35 / 100 = 45.95 gms of water