[kiki]

Question #1: How do I prepare 2.0 x 10^-4M DCPIP titratnt solution?
Question #2: How do I prepare 100ml of 0.8M H3PO4 from 85% stock solution?
Question #3: 100g of orange juice contains 50mg ascorbic acid. How much of a 2.0 x 10^-4M DCPIP titratnt woul be required to titrate a 100g sample? What would be a good sample size.
 

[kiki]

DCPIP MW is 290.12. Its an organic dye with both acid/base and redox properties. In a weak acid it is red, blue in basic solutions. DCPIP is a good oxidizing agent and ascorbic acid is a good antioxidant.

[Nobby]

You need the molecular weights of the chemicals.  With m = n*M you can calculate the mass.
For the Phosphoric you need also the specific gravity.

[kiki]

this is what i have for question one...40ml X 1L/1000ml X .05363g/1L= 21.45x10^-4 g in 40ml water.. i made up the 40mL. i don't know how many to use.




this is what i have for question # 3
I have 50mg ascorbic acid.  Molar mass is 176.13gmol-1, so that is 0.05/176.13 = 2.838 E-4.  .  Molarity of DCPIP is 2*10-4.
So V=n/c = 2.838E-4/(2*10-4) = 1.4194L



and i have know idea how to do question numebr 2. please help soon. thanks you in advance

[kiki]

the only molecular weights of the chemicals i have is DCPIP and it is 290.12. how do i find any of the others. and how do i find the specific gravity and what do i use that for? I am really lost. i need lost of help, im sorry

[Nobby]

1. m = n*M  m = 2* 10^-4 mol * 290.12 g/mol = 0.058 g

This has to be dissolved in 1 l water.

2. H₃PO₄ M = 98 g/mol

m = n*M  m = 0,8 mol *98 g/mol = 78,4 g  100% This is the value for 1 l. For 100 ml you need 7,84 g

85% means you need more 9.223 g

Specific gravity is 1,689 g/cm³

Rho = m/V  V = m/Rho  V = 9,223 g/1,689 g/ml = 5,46 ml