# Need help with titrations and buffers

1. Apr 18, 2005

### bohemian

I have two homework questions that don't make sense at all. I don't really know what formulas to use exactly. Here they are:

1. Molar mass of a certain metal carbonate, MCO3, can be determined by adding an excess of HCl acid to react with the carbonate and then "back-titrating" the remaining acid with NaOH.
a. Write an equation for these reactions
b. In a certain experiment, 20.00 ml of 0.800M HCl were added to a O.1022 gram sample of MCO3. The excess HCl required 5.64 ml of 0.1000M NaOH for neutralization. Calculate the molar mass of the carbonate and identify M.

and

2. Calculate the volume in ml of 6.0 M NaOH that must be added to 0.500 L of a buffer made of 0.0200M acetic acid and 0.0250M sodium acetate, in order to obtain a final pH of 5.75.

Any help to get me started on these would be greatly appreciated. My homework is due on Wed. so if anyone could reply back before then, that would be great. Thank you.

2. Apr 18, 2005

### dextercioby

I can help u with the first.From the notation,i'd suspect that the metal ion is divalent so the reactions would go

$$MCO_{3}+2HCl\rightarrow MCl_{2}+CO_{2}\uparrow+H_{2}O$$

$$NaOH+HCl\rightarrow H_{2}O+NaCl$$

Daniel.

3. Apr 18, 2005