The ammonia concentration of a solution is determined by titrating with aqueous hcl (previously standardized against na2co3) using a ph meter. which of the following errors will lead to a measured concentration of nh3 that is higher than the actual concentration? (a) some of the na2co3 used in the standardization is spilled before being transferred to the titration flask. (b) the glass stirring rod used to stir the ammonia solution is wiped with a paper towel after each aliquot of hcl is added. (c) the ammonia solution is allowed to stand in an open beaker for an hour before being titrated. (d) the ph meter has been miscalibrated so that all readings are 2.00 ph units higher than the actual ph.