Guide
1
ratio, ie the number of standing in front of the molecules of the chemical formula applies to all characters, and each is multiplied by the index of each character!It is multiplied, and does not add up!It may seem incredible, but some students add up the two numbers instead of multiply.
2
In other words, if the left side reactions recorded:
2Na3PO4 + 3CaCl2 = ... This means that the reaction took 6 sodium atoms 2 phosphorus atoms, eight oxygen atoms, three atoms of calcium and 6 atomschlorine.
3
number of atoms of each element of the starting materials (ie, located on the left side of the equation
) must match the number of atoms of each element of the reaction products (respectively, under its right-hand side).
4
Consider this rule by writing to the end of the reaction equation sodium phosphate with calcium chloride.For greater clarity, remove from the left side of the equation coefficients .Na3PO4 + CaCl2 = Ca3 (PO4) 2 + NaCl
5
formed during the reaction is practically insoluble salt - calcium phosphate - sodium and chloride.How to place factors ?Just note that the phosphate ion (PO 4) in the right side of the index is equal to two.Therefore, in order to equalize the amount of phosphorus and oxygen atoms on the left and right parts of the molecule to the formula of sodium phosphate should be put ratio 2. Get: 2Na3PO4 + CaCl2 = Ca3 (PO4) 2 + NaCl
6
You see,that the amount of phosphorus and oxygen atoms equalized, but yet different number of atoms of sodium, calcium and chlorine.On the left side: sodium - 6 atoms of calcium - 1 atom of chlorine - 2 atoms.In the right part, respectively: sodium - one atom of calcium - 3 atoms, a chlorine - 1 atom.
7
equalizes the number of sodium atoms, attributing factor of 6 to a molecule of sodium chloride.It turns out: 2Na3 (PO4) 2 + CaCl2 = Ca3 (PO4) 2 + 6NaCl
8
're equalize the last two elements.You can see that the left side of one calcium atom and two chlorine atoms, and the right - 3 atoms of calcium and 6 chlorine atoms.That is, exactly three times as much!Substituting the ratio 3 to a molecule of calcium chloride, will get the final equation: 2Na3 (PO4) 2 + 3CaCl2 = Ca3 (PO4) 2 + 6NaCl