1. a substance that can be separated into two or more substances only by a chemical change is a(n)

solution
element
mixture
compound

2.
which of the following materials is a substance?

air
gasoline
stainless steel
silver

3.
the first figure in a properly written chemical symbol always is

boldfaced
capitalized
italicized
underlined

4.
which of the following represents a compound?

h
h-3
h2o
o-16

5. what do chemical symbols and formulas represent, respectively?

elements and compounds
atoms and mixtures
compounds and mixtures
elements and ions

These are five questions and five answers.


1. A substance that can be separated into two or more substances only by a chemical change is a.

compound


Explanation:


i) solution is a homogenous mixture and it can be separated by physical media. For example, a brine: you can evaporate the water from the salt by heating the solution (brine)


ii) elements cannot be separated into two or more substances except by nuclear reactions.


iii) mixtures: heterogenous and homogenous mixtures can be separated by physical treatments.


iv) compounds are substaces composed of different elements bonded chemically; only chemical reactions break the chemical bonds or create new chemical bonds leading a compound to form other substances.

2. Which of the following materials is a substance?


silver


Explanation:

Substances have a definite composition that can only be modified by chemical reactions.


Elements and compounds are substances.


Silver is an element, such as sodium, gold, oxygen. You can find the list of the 118 known elements in a periodic table.


Mixtures, either homogenous or heterogeneous, can be separated by physical mechanisms and so they are not substances: air, gasoline, and stainless steel are mixtures because they have not a unique chemical formula but are formed by other compounds or elements in different proportions, i.e. with not a unique chemical formula.

3.The first figure in a properly written chemical symbol always is .


capitalized


Explanation:


This is a rule to write the symbols of the elements. For example, Na (sodium), Br (bromine), I (iodine), O (oxygen), Ne (neon).

4. Which of the following represents a compound?

H2O


Explanation:


That is the only chemical formula. The other representations are not valid chemical formulas. A chemical cormula can oly contain chemical symbols and subscript numbers, to represent the kind of atoms (elements) and how many of each (the subscrip).

5. What do chemical symbols and formulas represent, respectively?


elements and compounds


Justification:


1) The symbols are used to represnt elements, such as Na (sodium), Li (lithium), Be (berylium)

2) Chemical formulas represent compunds. For example: CO is carbon monoxide, CO2 is carbon dioxide, H2CO3 is carbonic acid, Na2CO3 is sodium carbonate.


Each compound has a unique chemical formula.

Ithink 2 is the correct

The phase where ice changes directly to gas is called sublimation