I am having a problem with making buffer of 0.2 M tribasic sodium phosphate dodecahydrate which has 6.8 pH. But I don't know how much weight I have to take
For that?

The buffer which contains 1:3 ratio, in which 1 part of 0.2 M tribasic sodium phospahte dodecahydrate and 3 parts of 0.1 N HCL in 1000 ml.

I want to make total 10 litters of buffer.

Please help me if someone can.