Answer:
Can you send the picture of this question
Synthesis reactions are reactions that occur when two different atoms or molecules interact to form a different molecule or compound. Most of the time, when a synthesis reaction occurs, energy is released and the reaction is exothermic
The compound sodium carbonate is a strong electrolyte because it completely dissociates when placed in water into its component ions. The equation of the reaction can be expressed as:

The dissociation leads to the formation of sodium and carbonate ions with the latter held together by its internal covalent bond.
This is unlike weak electrolytes that do not dissociate completely in water or aqueous solutions. Only a small fraction of the solute exists as ions in the solution.
More on strong and weak electrolytes can be found here: brainly.com/question/3410548
The error caused will lower the number of moles when he did not do the second heating.This question is related to the empirical formula.
<h3>What is Empirical formula ?</h3>
A formula giving the proportions of the elements present in a compound but not the actual numbers or arrangement of atoms.
The empirical formula is the simplest ratio of atoms in a given compound.
we know that heating is used to eliminate most of the water molecules which are attached to the compound in the question, it's given that the second heating was not performed by the students.
This means that there are still some water molecules attached to the compound. This will imply that higher mass will be calculated for the compound because the water molecules are also considered.
So now, if we look at the calculation for the number of moles of water in this, we can say that this will be lower than the actual amount.
This is because there are some unaccounted moles of water which are still attached to the compound and these will be accounted in the compound mass rather than the waters. Therefore, the number of moles will be lower.
Hence, The error caused will lower the number of moles when he did not do the second heating.
Learn more about Empirical formula here ;
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Answer:
to identify the element by using flame tests