Tens 6.50
ne elements hydrogen (
h and oxygen (o) are gases that react to make the stable
compound water (h. o. looking at the chemical formulas for the substances cobalt
(co and carbon monoxide (co), explain how you can tell which one is an element
and which one is a compound? (6.sc)

Is the atomic theory known, for certain, to be true?

No; a theory, as all scientific principles, is never certain. It is permanently subject to testing and experimental verification. Even if a theory is found to agree with all of the available observational data, and all of its predictions have been found to be ``correct'', i.e. borne out by all observations until today, it may yet be disproved by tomorrow's more precise observations. It is, in fact, the attempt to disprove the existing theories which is the purpose of most scientific experimentation.

[2.2]

Carbon atoms are about 25% lighter than oxygen atoms (the ratio of their weights is 3 to 4). What is the weight ratio of the carbon and oxygen that go into the formation of carbon monoxide? Answer the same question for carbon dioxide.

Carbon monxyde has the chemical composition CO, i.e. there is one carbon atom for every oxygen atom; therefore the weight ratio of carbon to oxygen in this compound is just the weight ratio of the atoms, i.e. 3 to 4. In carbon dioxide, tex2html_wrap_inline121 , there are two oxyen atoms per carbon atom, so the carbon to oxygen weight ratio in carbon dioxide is 3 to 8.

[2.4]

Which of these is a pure compound, which is an element, and which is neither: (a) pure water, (b) oxygen gas, (c) liquid mercury, (d) tex2html_wrap_inline123 , (e) U, (f) air,

(g) He, (h) carbon dioxide, (i) tex2html_wrap_inline125 , (j) polluted water?

Explanation:

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