How much free chlorine is there in a 10.5% Sodium Hypochlorite solution?
Depends on the pH. Most chlorine bleach is stabilised to the alkaline side, so it (mostly) exists as the hypochlorite anion. (OCl-) As you shift the system to the acid side you first form free hypochlorous acid (between approx pH 4 - pH5.5 all of the hypochlorite exists as hypochlorous acid HOCl), and below pH4 it starts to release free chlorine. If you send it very acid, it releases all of the product as chlorine gas. So, in 1 litre of a 10.5% (w/v) Sodium hypochlorite solution, you have 105g of Sodium Hypochlorite (NaOCl - m.w. 74.44) which is 47.62% by weight Cl ( or 50g). So you have 5% available chlorine (w/v) in a 10.5% Sodium hypochlorite solution.
How does sodium hypochlorite react with hydrochloric acid?
Sodium hypochlorite is a chemical compound with the formula NaClO and it is composed of a sodium cation (Na+) and a hypochlorite anion (ClO−).It may also be thought of as the sodium salt of hypochlorous acid. When dissolved in water it is commonly known as bleach. If you mixed with HCl you would get Chlorine gas released and would make you start coughing. The gas if it got in your lungs would hydrate make HCl and other acids scarring your lungs. Overexposure would cause death. Sam Castar has the right equation in his answer although chlorine gas has been said to be yellow-green.
Is it safe for me to use a sodium hypochlorite / ammonium chloride solution, or will this create chlorine gas?
Ammonium chloride is an unstable salt, NH4Cl which decomposes when warmed to produced NH3(g) and HCl(g), nether of which are pleasant to smell. But ammonium chloride is not ammonia. Ammonia is NH3 and it is a gas at room temperature. Often we see a bottle containing a liquid labeled as "ammonia". This is actually a solution in which ammonia gas has been dissolved in water. There is a misconception which abounds that combining chlorine bleach and an ammonia solution will produce chlorine gas. Instead of chlorine, you get a foul-smelling, somewhat toxic gas called "chloramine", or more specifically, monochlorammine, which has the chemical formula NH2Cl. It is what you smell around pools when people say they smell "chlorine."
What rate do you dilute sodium hypochlorite to clean a driveway and can you apply it with a tank sprayer?
sodium hypoCHLORITE is the same thing as bleach, just a different form. the best way to etch your concrete is muriatic acid, spray it on and rinse out your sprayer with water,