Here's how the master chef in a classy Chinese restaurant I worked in tenderised all chicken using baking soda. The amounts  and timings need to be precise or you risk failure. The amounts below are for ONE chicken breast; multiply the amounts for more than one. Keep the timings the same as below irrespective of how many breasts you are using. This method gives moist, tender shiny chicken.

1/2 teaspoon baking soda 
1 chicken breast sliced as thin as possible across or with the grain - your preference (interestingly, the Master chef insisted his chicken breast be sliced very thinly with the grain). Sprinkle baking soda over chicken and mix gently but thoroughly to make sure it's evenly distributed. Cover in refrigerator for 10-12 mins. Remove and place in strainer. Rinse with lots of cold water gently but very thoroughly to remove all baking soda. Pat dry thoroughly with paper towels. 

Place in a bowl with 1/2 teaspoon of corn starch and I teaspoon of Chinese rice wine. Cover and refrigerate for 15 mins.

Then use in recipe as per usual. Don't overcook; it will take 30 secs to 1 min only in a very hot wok.