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April 25, 2014

Homework Help: plz help now, chemistry

Posted by Beautiful on Thursday, December 21, 2006 at 6:32pm.

How do you write chemical formulas? For example how so you right a chemical formula for calcium fuoride?

Calcium flouride would be CaF2

This is because ..

Calcium symbol - Ca
Flourine symbol - F

you would write CaF

BUT you must consider charges

calcium has a 2+ charge
and Flourine has a 1- charge.

The charges criss-cross and so the 2 charge goes on the F and the 1 charge goes on the Ca. Since 1 can be assumed we don't write it.

Your final answer would be CaF2

is the two a subscript


yes

A good response. It might be worth noting that the charges do criss-cross but the sign of the charge is ignored. For example, for sodium oxide, the charge on Na is +1 and the charge on oxygen is -2; therefore, the formula is Na2O (not Na-2O with the 2 being a subscript, Na2O. We DON'T write it as Na-2O. It is SO MUCH trouble, however, to write the subscripts, we just assume everyone knows Na2O is Na2O. Thanks for using Jiskha.

In the lab, 20.0 g of sodium hydroxide is added to a beaker giving it a total mass of 128.4 g. Sulfuric acid is added until all of the sodium hydroxide reacts. After heating, the total mass of the beaker and the dry compound is 142.3 g. Caculate the percent yeild.

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