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A mole is like a dozen - it is a number of something. You can have a dozen people (12 people), a dozen oranges and so on. A dozen is useful for big objects like oranges, but atoms and molecules a...

x₁ = (-b + (b² - 4ac)^1/2)/2a and x₂ = (-b - (b² - 4ac)^1/2)/2a. So with the values a = 1, b = 3 and c = 2: x₁ = (-3 + (3^{2 <...}

x²+2x+1=0, (x+1)(x+1)=0, (x+1)²=0. So x=-1

I recommend using study cards.  Write down the spanish word on one side and the english word on the other side. Set yourself the task of learning 5 words a day and ask someone to test you.

To form Al2O3 you need both Al and O2 (oxygen gas is a dimer):

Al + O2 -> Al2O3

But this equation is not balanced. To balance it, first equate the number of oxygen atoms:

Al + 3O2 ...