Difference Between Baking Soda and Baking Powder

Both baking soda and baking powder are leavening agents, which means they are added to baked goods before cooking to produce carbon dioxide and cause them to 'rise'. Baking powder contains baking soda, but the two substances are used under different conditions.  Both are white powders, odorless and nearly indistinguishable. Yet both help your baked goods to rise.

Baking Soda

Baking soda is pure sodium bicarbonate. 

When baking soda is combined with moisture and an acidic ingredient (e.g., yogurt, chocolate, buttermilk, honey), the resulting chemical reaction produces bubbles of carbon dioxide that expand under oven temperatures, causing baked goods to rise. 

When heated, It leaves an unpleasant, alkaline flavor behind to avoid that always mix with acidic food (like lemon juice or another citric acid carrier), it neutralizes and leaves no bitter taste. This acid also helps the carbon dioxide gas release more quickly.

The reaction begins immediately upon mixing the ingredients, so you need to bake recipes which call for baking soda immediately, or else they will fall flat!

Baking Powder

Baking powder contains sodium bicarbonate, but it includes the acidifying agent (cream of tartar), and also a drying agent (usually starch). 

Baking powders some gas is released at room temperature when the powder is added to dough, but the majority of the gas is released after the temperature of the dough increases in the oven. Addition of starch helps to absorb moisture, and thus prolong shelf life by keeping mixture alkaline and keeping acidic components from reacting prematurely.

In Recipes:
"Some recipes call for baing soda, while others call for baking powder. Which ingredient is used depends on the other ingredients in the recipe."

    'Commonly Used In':

• Baking soda used recipes like cookie, pancakes, quick breads, and other baked and fried foods.
• Baking powder is a common ingredient in cakes, biscuits, muffins, scones and American-style biscuits .

Always add baking soda with another acidic ingredients like buttermilk, orange juice, cream of tartar, lemon juice, yogurt, cocoa, vinegar etc. If wanted to use milk in recipe then add tbsp of vinegar each cup of milk to form buttermilk.

Baking powder contains both an acid and a base and has an overall neutral effect in terms of taste. Always use baking powder with neutral tasting ingredients like milk. If wanted to add some acidic ingredient like lemon or orange juice then smply add 1/4 tsp baking soda for each tsp of baking powder in the original recipe. 

Substituting:

You can substitute baking powder in place of baking soda (Baking soda is 4 time stronger than baking powder)

You can not use baking soda when a recipe calls for baking powder. 

*Note: This post will change as get more information Source:about.com, wiki.