Chemists say that some chemicals are strong bases and some chemicals are weak base. Sodium bicarbonate is a strong base: if you put some of it into water and measure its pH, you will find a number much higher than 7. Ammonia is a weak base: if you put the same amount of ammonia into water and measure its pH, you will find that the number is not much higher than 7. The stronger the base, the more quickly it will react with an acid like vinegar.