Re: How do u make a 6 volt battery?

You are given copper metal, magnesium metal, and copper sulfate.  I presume you are also given 
some water and perhaps a borosilicate beaker.  You will need the water to dissolve the copper 
sulfate in.  The beaker would be convenient, but you could make a container out of the copper.

By definition a battery is an assembly of similar devices.  In electrochemistry a battery is usually a 
series assembly of electrochemical cells.  The positive end of one cell is connected to the 
negative end of the next cell in the series.  Thus if you have a battery of two cells in series the 
voltage delivered by the battery would be twice that of either cell.

For example the twelve volt lead-acid battery in a car is actually six individual cells connected in 
series.

Hve you written the half-cell reactions for the magnesium/copper sulfate/copper cell?

On one side magnesium metal will be oxidized to magnesium sulfate.

On the other side copper sulfate will be reduced to copper metal.

If you connect the two metals together by a resistor electrons will leave the magnesium, flow 
through the resistor, enter the copper wire and reduce the copper sulfate.

Your job, and I leave it to you, is to go to the electromotive force table which you should have in 
your textbook and estimate the potential difference that you would measure between a copper 
wire and a magnesium wire stuck into a solution of coppersulfate.  Then you would divide six by 
that number to get the number of cells you would need to place in series to get six volts.

Or you could assemble a single cell and measure the voltage with a voltmeter.  If you have the 
supplies at hand that might be easier, and certainly more fun, than looking up stuff in a table.

[Actually magnesium is a poor choice for this exercise as it tends to form a poorly conducting 
oxide coating.]

The word battery has been so corrupted that in the vernacular a AA battery is used to refer to a 
single 1.5 volt cell of a certain size.  The 9-volt battery is actaully of battery of six 1.5 volt cells 
in series.