Many household cleaners, particularly toilet cleaners and some drain cleaners have acid in them. this is the equation representing hydrochloric acid plus bleach. naclo + 2 hcl →cl2 + h2o + nacl if you mix bleach with acidic cleanser, a very noxious gas that can cause respiratory problems will be released. your sense of smell can detect this gas in air at concentrations as low as 0.08 parts per million and at that level, it is basically an irritant. levels as low as 15 parts per million can cause severe throat irritation while levels of 50 parts per million or above are very dangerous. what is this gas?