calculations

Question 1

Unknown amount of cystein was dissolved in 500 ml of water. from this solution 20 ml was titrated against phenopthalein using 15.5ml of 200mM NaOH. calculate the molar concentration of cystein.

Answer 1

15,5 * 0,2 / 1000 = 3,1 * 10^-3

3,110^3/2010^-3 = 0,155 M

Question 2

How many grams of vitamin C is in 600 ml solution, if to titrate 12 ml of this solution 55 ml of 0,005 M DCPIP has been used. (Vit. C 176 g/Mole)

Answer 2

0,005 * 55 / 1000 = 2,75*10^-4

2,75*10^-4 = 12 ml
1 mole = 176 g

2,75*10^-4 * 176 = 0,0484g

0,0484g * 0,6L / 0,012 L = 2,42g of vit c

Question 3

How many mg of vitamin c is non oxidized in the expired vit c preparation, which was dissolved In 15 ml of water, if to titrate this solution 16 ml of 0,01 M DCPIP has been used (vit c 176g/mole)

Answer 3

160,01M/1000 = 1,610^-4

1,6*10^-4 = 15 ml
1 mole = 176 g

1,6*10^-4 * 176 = 0,02816g

28 mg

Question 4

15 ml of TCA was added to 7,5 ml of milk, as well as 22,5 of water. after a while the mixture was filtered and 10 ml of deprotinized milk sample was added into the erlenmayer flask, as well as 5 ml of 0,1M AgNo3. After formation of AgCl precipitate adding 1ml of chloroform, an analyte was titrated by 0,1 M NH4CNS in the presence of FE3+ 4,25ml titrant was used . calculate mg% of the chloride in the milk.

Answer 4

NH4CNS = 0,00425L * 0,1 M = 4,2510^-4
AgNO3 = 0,005L * 0,1M = 510^-4

Chlor:
510^-4 - 4,2510^-4 = 0,75*10^-4

how many ml of milk:
7,5 + 22,4 + 15 = 45
7,5 *10/45 = 1,67 ml

0,7510^-435,5g(Cl Mm) = 2,66mg

mg% = 100 * 2,66mg / 1,67 = 159,3