Most of the students I tutor are having difficulty in learning chemistry especially to understand chemistry. Actually it is true for most people, even people who have studied chemistry for many years now. This is because chemistry is a hard subject to learn and even more difficult thing is the use of math in chemistry concepts. I have been doing chemistry tutoring for 8 years now and one thing I found common is that most students do not know the meaning of "mole" a common unit use in chemistry. Many students do not understand the meaning of mole, although they know how to solve problems relate to mole and molar mass. This is because sometimes in science even we do not understand the concept but if are are smart in math, we can figure out the math.
The way I approach sciences over the years is that when I do not understand any science concept, I try to visualize it and make a mental picture about the it. I try to put the concept in a real life perspective and then solve the problem. The advantage of this way of learning is that science concepts are related and links to each other. And when we visualize something, it stays in our mind more often than not. For example, mole is a concept like dozen in math. It means number, also known as Avogadros' Number. Like dozen, which means 12 of something, a mole is a number equal to 6.022*10*23 particles! It means that when we have one mole of something we have this number. Another words, it does not matter if it is element, atom, ion, or compound as long as you have 1 mole of something, it contains 6.022*10*23 particles.
Sodium is a metal whose atomic number is 11 and mass number is 23. The easy way to find the number of moles a particular amount of sodium contains is to look at the periodic table and see the molar mass (mass of one mole) of sodium. If we look at the periodic table we find that the molar mass of sodium is 23 g of sodium, which means that if we have 23 g of sodium we have 1 mole of sodium. Similarly, if we have 46 g of sodium, we have 2 moles of sodium, 69 g will have 3 moles, 92 g will have 4 moles of sodium and so on. So if one mole contains 6.022*1023 number particle, 2 moles will have 12.044*10*46 of particles.