I think you may be asking about the use of baking soda to either use as an exfoliant or possibly to reduce the oiliness of skin. I have seen articles advocating this… but would advise against using either on skin.
Firstly, in answer to your query, baking soda is sodium bicarbonate and needs to come into contact with an acid and water in order to make carbon dioxide, (which makes a batter light and full of little bubbles). Baking powder is also sodium bicarbonate but with the acid added already, so it just requires water to make the carbon dioxide.
As it is a powder and not a solution, it doesn’t strictly have a pH, but when you add water to it and apply it to skin, it is alkaline with a pH of around 8 - the acid mantle of skin is around pH 5. You can put more alkaline or acidic solutions on your skin without harming it, but it should be done under direction - there is usually a good reason to do this and damage can result if done in excess. If a skincare product has a particularly low pH, it is usually necessary to allow an ingredient to work. I believe some acid peels are neutralised using sodium bicarbonate, but it wouldn’t be recommended for home use.
If you regularly wash skin in baking soda, the acid mantle could become compromised. It is there to protect the skin from damage and infection and If it is disrupted, skin can be vulnerable to inflammation and spots.
Occasional use shouldn’t do any significant damage, providing you are not sensitive to it; some people react with redness, swelling, itching and cracked skin. If you don’t react adversely, then you could use this as an exfoliating scrub occasionally, although I think there are better alternatives.
It’s not the most exciting method, but I would always advise going gently and slowly with skin. It is already doing a good job and the most important consideration is to simply help it to do what it is designed to do. Gently rubbing skin with a cotton face cloth should be all the exfoliating most skin needs.
Strengthening the skin will get a longer-term result, if it has become inflamed or damaged, or if it just getting a tad old! So keep it clean, use a hydrosol, a gentle cleanser or jojoba, coconut or even olive oil to remove city grime or makeup. Then it needs moisture and some protection from the environment. Use a good quality moisturiser - this needn’t be expensive and make sure you use something occlusive, if the weather conditions are harsh and a good broad spectrum SPF if the sun is hot enough to burn.
Remember that the skin needs vitamins to function and will start to be problematic if supplies run low. Simply eating them is the easiest way to prevent problems. Vitamins A, B and C are all found in the skin and it needs a constant supply to keep these at optimum levels. If you are not eating enough, topicals creams and serums can help, but it is better to prevent the depletion before it happens.