Can anyone offer me real help?

Question

I need help with these two problems; please help me!

1.A soft drink contains an unknown amount of citric acid, C6H8O7. If 100. mL of the soft drink require 33.51 mL of 0.0102 M NaOH to neutralize completely the citric acid, how many grams of citric acid (molar mass = 192.13 g/mol) does the soft drink contain per 100. mL? The reaction of citric acid and NaOH is

C6H8O7(aq) + 3NaOH(aq) --> Na3C6H5O7(aq) + H2O(l)

2. In the photographic process, silver bromide is dissolved by adding sodium thiosulfate.

AgBr(s) + 2Na2S2O3(aq) --> Na3Ag(S2O3)2(aq) + NaBr(aq)

If you want to dissolve 0.250 g of AgBr (molar mass = 187.8 g/mol), how many milliliters of 0.0138 M Na2S2O3 should you add?

Answer 1

1.) Step 1: Find how many moles of NaOH you added to the drink.
moles = volume * molarity
moles = .03351 L * 0.0102 moles/L
moles = 0.000341802 moles NaOH

Step 2: Since you need 3 moles NaOH per mole of C6H8O7, you must have 0.000113934 moles of C6H8O7.

Step 3: Find the mass of C6H8O7.
192.13 g/mol * 0.000113934 mole = 0.0219 g C6H8O7 (solution!)

2.) In the photographic process, silver bromide is dissolved by adding sodium thiosulfate.

AgBr(s) + 2Na2S2O3(aq) --> Na3Ag(S2O3)2(aq) + NaBr(aq)

If you want to dissolve 0.250 g of AgBr (molar mass = 187.8 g/mol), how many milliliters of 0.0138 M Na2S2O3 should you add?

Step 1: Find how many moles of AgBr you have:
Moles = mass / molar mass
moles = .250 g / 187.8 g/mol
moles = 0.0013312 moles

Step 2: Find how many moles of Na2S2O3 you need:
0.0013312 moles AgBr * 2 = 0.0026624 moles Na2S2O3

Step 3: Find how many mL you need of 0.0138 M Na2S2O3.
molarity = moles / volume
volume = moles / molarity
volume = 0.0026624 moles / 0.0138 M
v = 0.192928 L
v = 192.93 mL (solution!)

Answer 2

You might want to ask your teacher for help.

Answer 3

good luck with that!