Burning a magnesium ribbon in the air is an addition reaction while heating potassium manganate 7 is a decomposition reaction.
<h3>Addition and decomposition reactions</h3>
Magnesium burns in air to produce magnesium oxide as follows:

Potassium manganate 7 burns to produce multiple products as follows:

Thus, the MgO will be heavier than Mg. On the other hand,
will be less heavy than
.
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When q is the heat energy in joules (J)
so, according to this formula, we can get q (in joule unit):
q = M*C*ΔT
when M is the mass of the water sample = 1.85 g
C is the specific heat capacity of water = 4.18 J/g.°C
and Δ T is the difference in temperature (Tf-Ti) = 33 - 22 = 11°C
So, by substitution, we will get the value of q ( in Joule):
∴ q = 1.85 g * 4.18 J/g.°C * 11 °C
= 85 J
Hey there!
The answer as well as the explanation is in the image attached. Let me know if there's anything you're unable to see.
Hope this helps!
Answer:
about 0.9 mol
Explanation:
there are 22.990 g/mol of Na
20.7/22.99 = 0.900391 mol
about 0.9 mol