12. How many moles of atoms are present in 154 g of Na2O? A) 2.48 mol
B) 7.45 mol
C) 51.3 mol
D) 0.827 mol

Explanation:

We are asked to convert an amount in grams to moles. To do this, we use the molar mass. This is the number of grams in one mole of a substance. It is the same value numerically as the atomic mass on the Periodic Table, however the units are grams per mole, not atomic mass units.

Look up the molar masses for the individual elements.

Look back at the formula: Na₂O. Notice there is a subscript of 2 after sodium. This means there are 2 atoms of sodium in every molecule, so we have to multiply sodium's molar mass by 2 before adding oxygen's.

Set up a ratio using the molar mass.

Multiply by the given number of grams.

Flip the ratio so the grams of sodium oxide can cancel each other out.

The original measurement of grams given has 3 significant figures, so our answer must have the same. For the number we calculated, that is the hundredth place.

The 4 in the thousandth place tells us to leave the 8.

There are 2.48 moles of sodium oxide in 154 grams, so choice A is correct.

the formula for the conversion of temperature from degree celsius to kelvin is:

the sample of water at is converted to kelvin temperature by using the above formula as:

on comparing the two samples of water at or we can say that at and at respectively. the difference between the temperatures of two samples of water is:

hence, one can say that the sample of water at is greater than the sample of water at by .