[NTP]

Hi,

Hi,

CAN SOMEONE EXPLAIN THE REASONING BEHIND THIS SUM, THANK YOU.

Write down the mass of calcium which has the same number of atoms as 12g of magnesium.



Not sure if I worked it right, I first worked out the number of atoms of 12gmagnesium and the result was 3 *10 ²³. Then I used this and to find the mass of calcium by doing moles of atoms= mass / ram, and my final answer was 1.2 *10 ²⁵

wOULD APPRECIATE A FEEDBACK , THANK YOU

[AWK]

12 g of Mg is equivalent to 1/2 mole. How many grams weights 1/2 mole of Ca?

[NTP]

20g is 1/2 of Ca

[xiankai]

and there is your correct answer

[NTP]

But if the elements are from different groups not like it was with the previous answer both group 2 elements, it has to be worked different?
Example:

Write down the mass of silver which has the same number of atoms as 3g of aluminium.

I worked it out the same way and my answer is 7.2 * 10²⁴g of Ag. Not sure if it correct.

[AWK]

3 g of Al is approx. 1/9 mole - take 1/9 mole of Ag

[DevaDevil]

Write down the mass of silver which has the same number of atoms as 3g of aluminium.

I worked it out the same way and my answer is 7.2 * 10²⁴g of Ag.

O.o, that would mean that 3g aluminium has the same amount of moles as 7,200,000,000,000,000,000 tonnes of silver?

Somehow I don't think that's correct



You do not need Avogadro's number for these calculations. Just calculate mass to moles (mass [g] / molar mass [g/mol] = moles, do not calculate to molecules) and then back to mass of the other element.
As a mol of a compound has the same number of molecules independant of the compound, moles are easier to work with than molecules. That is precisely why the unit was introduced

[AWK]

I worked it out the same way and my answer is 7.2 * 1024g of Ag. Not sure if it correct.

It does not matter 10^-24 or 10²⁴, isn't it?

[NTP]

I worked it out this way using moles so it is correct now hehe 

Number of moles  = mass / ram    (3g of Al)

N = 3/ 27
N= 0.1111111

Therefore: number of moles =  mass /ram   (mass of Ag).
                  0.1111111  =    mass / 108
                0.1111111 * 108
 Mass of Ag = 12g

My Answer is 12g of Ag .
Still not sure but hehe

[xiankai]

right on the dot again you are. its quite easy and merely involves simple arithmetic.

[NTP]

Thank you all for the help