you are right on all the ones you did
Pure substances contain a single type of chemical species, either element or compound. Elements cannot be further broken into simpler units by chemical methods. If we consider a sample of elements, it has a single type of atoms present in it. A compound has one or more atoms bound together chemically. Compounds can be broken down into simpler units by chemical means. When we consider a sample of a single compound say water, it has all the pure water molecules. Hence, elements and compounds are pure substances.
The percentage by mass of water in Na2CO3.10H2O from the calculation is 62.9%
<h3>What is percentage by mass?</h3>
The term percentage by mass refers to the amount of a particular moiety by mass in a molecule.
In this case, we know that the molar mass of Na2CO3.10H2O is 286 g/mol the molar mass of the 10 moles of water is 180 g/mol hence the percentage by mass of water in the compound is; 180 g/mol /286 g/mol * 100/1 = 62.9%
Learn more about percentage by mass: brainly.com/question/16885872
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