This is the chemical formula for talc (the main ingredient in talcum powder):
mg3( si2o5)2(oh)2
an analytical chemist has determined by measurements that there are 21.4 moles of magnesium in a sample of talc. how many moles of silicon are in the sample?

28.53 moles of silicon

Explanation:

Chemical formula helps us to see which elements are contained in a compound. If correctly written, it can also help us see how much atoms of each element are there.

For this particular case, in one molecule of talc, we have;

3 atoms of Mg

4 atoms of Si

12 atoms of O

2 atoms of H

From here, we can find the ratio of any two atoms from the molecule. So, we can say that the ratio of Mg: H is 3:2, or that ratio of O: Mg is 12:3 etc.

Now, if we expand this concept on moles, we can easily solve this problem.

We know there are 21.4 moles of Mg and want to know how many moles of Si are there. Since we can see the ratio of Mg: Si which is 3:4, we write a proportion:

3 : 4 = 21.4 : x

x = 21.4 • 4 / 3

x = 28.53 moles of Si

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g