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Solution Stoichiometry, Titrations. Please Help!

Submitted by PollysCracker on Tue, 11/30/2010 - 21:35

My teacher assigned this homework without giving us notes to go from. Please explain these problems for me.

1. What mass of NaCl is needed to precipitate the silver ions from 20 mL of 0.100 M AgNO3?

2. What mass of NaOH is needed to precipitate the Cd2+ ions from 25.0 mL of 0.500 M Cd(NO3)2 solution?

3. a) What volume of 0.115 M HCIO4 solution is needed to neutralize 50.00 mL of0.0875 M NaOH?
   b) What volume of 0.128 M HCl is needed to neutralize 2.87 g of Mg(OH)2?
   c) If 25.8 mL of AgNO3 is needed to precipitate all the Cl- ions in a 785 mg sample of KCl(forming AgCl), what is the molarity of the AgNO3 solution?
   d) If 45.3 mL of 0.108 M HCl solution is needed to neutralize a solution of KOH, how many grams of KOH must be present in the solution?

Thank you.


Very useful equations:
no. of moles = volume in litres x molarity
These are derived from the above
volume in litres = no.of moles/molarity
molarity = no.of moles/volume in litres

Also the formula mass of a compound in grams is the molar mass eg H2O = 1x2 +16 = 18g/mole

Mass of substance = number of moles x molar mass

1. You can find number of moles AgNO3
Each moles AgNO3 has 1 mole of Ag+ (from its formula). So you know the number of moles of Ag+ ions
You then need to find the ratio in which Ag+ reacts with Na+Cl-. This is the stoichiometric equation
Na+Cl-(aq) +  Ag+(aq)  --->  AgCl(s) + Na+(aq). This can be written as Cl-(aq) + Ag+(aq) ----> AgCl(s)
So this tells you that 1 mole of NaCl is needed per mole of Ag+ (or AgNO3)
So you also now know moles of NaCl needed. Find the mass of this number of moles.
2. is similar
3. Find moles of NaOH. Find moles of HClO4 from the stoichiometric equation.
For the rest I have given the equations you need at the start.

Try them and post your work