a 3.81 g sample of NaHCO3 was completely decomposed. After decomposition, Na2CO3 had mass of 2.86g. Determine mass of H2CO3 produced.

1.67g H2CO3 are produced

Explanation:

Based on the reaction:

2NaHCO3 → Na2CO3 + H2CO3

2 moles of NaHCO3 produce 1 mole of Na2CO3 and 1 mole of H2CO3

To solve this question we need to find the moles of Na2CO3 = Moles of H2CO3. With their moles we can find the mass of H2CO3 as follows:

Moles Na2CO3 -Molar mass: 105.99g/mol-

2.86g Na2CO3 * (1mol/105.99g) = 0.02698 moles Na2CO3 = Moles H2CO3

Mass H2CO3 -Molar mass: 62.03g/mol-

0.02698 moles  * (62.03g/mol) =

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

it's c. elements are placed in rows based on how may valencies electrons have.