How would you balance Na2B4O7 + H2SO4 + H2O --> H3BO3 + Na2SO4?

##Na_2B_4O_7## + ##H_2SO_4## + ##5H_2O## ##rarr## ##4H_3BO_3## + ##Na_2SO_4##

You first balance the metals, namely Sodium (##Na##), but in this case it is already balanced, 2 on the left of the arrow and 2 on the right.

Next you do the non-metals, starting with anything but Oxygen (##O##) and Hydrogen (##H##), which in this case is Sulphur but since its part of a polyatomic ion, being Suphate (##SO_4##) you balance it as a whole, in this case they are both balanced though.

Next is Boron (##B##), on the left there is 4 and on the right there is one, so you add a 4 before the ##H_3BO_3## to balance it.

The you balance the Hydrogen (##H##) atoms, on the left there is 4 and on the right there is 12 after putting a 4 in front of (##H_3BO_3##). So you add a 5 to the water molecule on the left such that it doesn't effect the Sulphate ion, and in doing so balances the amount of Hydrogens (12 each side).

Everything should now balance, including Oxygen (16 on left and 16 on the right), if it doesn't, just keep trying by putting different values of coefficients before each molecule until it works out.

Remember that the coefficients should be the lowest value possible, and must not be fractions.

Hope I helped :)