b. How many mEq of NaOH must be added in order to adjust the volume and
concentration to 100 mL of 1.0 Eq/L NaOH solution? In order to determine how many
mEq of NaOH must be added you must first ascertain the number of mEq present in the
desired volume and concentration of solution. You desire 100 mL of a 1.0 Eq/L NaOH.
With this information the number of mEq desired can be calculated.
L
1.0 Eq
1000 mEq
100 mL X --------X -------- X ---------- = 100 mEq of NaOH desired
1000 mL
L
Eq
mEq needed = mEq desired -- mEq in flask
100 mEq -- 81 mEq = 19 mEq needed
Thus, 19 mEq of NaOH needs to be added to the flask and sufficient quantity
(q.s.) volume to 100 mL in order to obtain a 1.0 Eq/L NaOH solution.
c. How much stock 10 Eq/L NaOH must be added to the flask in order to adjust
the concentration to 1.0 Eq/L? Multiply the number of mEq needed times the
concentration of the stock along with appropriate conversion factors for the volume and
concentration to obtain the desired results.
Eq
L
1000 mL
19 mEq X ----------X ------X -------- = 1.9 mL
1000 mEq 10 Eq
L
1.9 mL of the stock solution must be added and the solution Q.S. to 100 mL
to yield the desired solution.
MD0837
7-7