chem 3&4

how did the magnesium lab demonstrate the law of constant composition?

The straight line created on the graph represents the relationship between the oxygen and magenesium. the fact the line created is straight demonstrates the constant ration between the oxygen & magnesium, which dalton describes in his law, all compounds of atoms have a constant ratio.

What was the purpose of graphing the points and drawing a best fit line in the magnesium lab

This acted as an average of all the results, and also showed the linear relationship between the oxygen and magnesium, which also excludes outliers

Are all molecules compounds? explain why or why not?

no, molecules can be two or more atoms of the same element where as compounds are atoms at different elements.

How are pure substances and homogenous mixtures similar?

They can both be made of chemical compounds with non-visble parts that look the same throughout

how do pure substances and homogenous mixtures differ

Pure substances can also consist of a singular element of compound, whereas homogenous mixtures are bonded atoms of two or more different elements

Homogenous mixture

are made up of multiple particles but they look the same throughout

ex: salt, water, air

Pure substancc example

O2

can a compound be a pure substance? explain why or why not?

yes, as long as that compound is the same throughout and not separated. Pure substances must be the same throughout so the compound must be consistent.

Physical Change examples

• melting boiling

• cutting paper

• breaking glass

Chemical Property

• baking soda reacts with vinegar to form a gas

• flammability

• sodium reacts with water

Heterogenous Mixture

can be easily seen & picked

ex: sushi, hot tea, salad, trail mix

Pure Substance

can be chemically decomposed

ex: gold, lead, oxygen

Problem question: Ivan goes camping, and a rodent gets into his food stock, chewing holes in the containers. As a result, his cooking oil gets mixed in with his ground coffee and his sugar crystals. Explain how he can separate and keep all substances, be specific about what methods he would use for each substance ( coffee grounds & sugar crystals are about the same size and neither will dissolve in oil).

Ivan can first filter the oil from the mixture using a cloth or strainer, leaving behind the coffee grounds and sugar crystals. Then, by dissolving the sugar in water and filtering again, he can separate the coffee grounds and recover the sugar through evaporation.

Chlorine has two naturally occuring isotopes, one with 18 neutrons & one with 20 neutrons. Which isotops do you think is more common and explain your reasoning.

The most common naturally occuring chlorine isotope is the isotope with 18 neutrons, as that would create an atomic of 35, which compared to the average mass ( 35.45 which is calcualated based on abdundance) is very near. A chlorine isotope with 20 would produce an atomic mass of 37, which although is close, would not be as close to 35. 45 as 35 amu. This is because the neutrons and protons create the atomic mass and chlorine has 17 protons. therefore, 17+18=35 & 17+20=37

is the number of electrons in a neutral atom enough info to identify the atom? explain why or why not

Yes, it is because in a neutral atom must match the protons within the atom. Since the number of protons in an atom never changes, the atom can be identified by the its atomic number on the periodic table

Describe two types of pure substances and give an example of each. How can you distinguish between the two?

You can have a sample that is a pure element where there is only one type of atom present

You can have a sample of a pure compound where there is only one type of molecule present (and that molecule must be made of atoms of 2 or more different elements.)

You can distinguish between the two because compounds can be broken down into elements (usually using extreme heat or electricity)

Must all compounds be molecules? Explain why or why not.

Yes all compounds must be molecules that is because by definition a molecule must have at least 2 atoms bonded together. A compound must consist of atoms of 2 or more elements bonded together so there must be at least 2 atoms to make up that compound.

How are all atoms of a given element similar? How can they differ?

All atoms of the same element must have the same number of protons and because atoms are neutral they must have the same number of electrons. Atoms of the same element can differ by having different numbers of neutrons and therefore different atomic masses.

4)Compare and contrast protons and electrons (give 4 similarities or differences)

protons charge = +1, electrons charge = -1

proton mass = 1 amu Electron basically zero mass

proton found in the nucleus electron found outside the nucleus in the electron orbitals

proton = atomic number = identifies the atom, electrons can be lost or gained during chemical reactions. They contribute to the chemical nature of the element.

What is the difference between a homogeneous mixture and a heterogeneous mixture and give one example of each.

A homogeneous mixture is the same throughout example = cranberry juice

in a heterogeneous mixture you can see the different parts of the mixture for example a pocket full of change (coins)

What is the difference between a chemical and a physical change?Give one example of a physical change and one example of a chemical change.

A chemical change (chemical reaction) the atoms are rearranged and new chemical substances are formed. In a physical change it is just a change of a physical property such as state of matter or mass the actual chemical composition of the substance does not change (the atoms are not rearranged.)

What is the difference between a chemical and a physical change? Give one example of each.

During a physical change the substance does not change it is just an alteration in a physical property such as state of matter (ex ice melting). A chemical change there is a rearrangement of atoms and a new chemical substance is made (ex solid sodium reacting with water to produce hydrogen gas)

Explain how Ryan could separate a mixture of ethanol, water, rocks and dirt. Use specific language as to what method is used to isolate each substance

• Ryan could filter out the liquids from the solids

• with the water and alcohol he could use distillation to separate the two liquids

• He could use hand separation and pick out the rocks from the dirt.

List 3 properties of Dalton's atomic theory

• matter is made up of small particles called atoms

-atoms of a given element are identical

-atoms of any given element are different from atoms of any other element

What is the law of constant composition

The law of constant composition states that atoms can combine to form compounds. A given compound will always have a constant ratio of the component atoms.

list 4 properties of metals

-shiny (luster)

malleable

ductile

can conduct heat and electricity

for positive ions

most are solids at room temperature

List two properties specific to the following chemical families

Alkali metals:

They form +1 ions

They are highly reactive

They are soft (you can cut them with a knife)

Halogens:

They are diatomic as gases

They form -1 ions

Are there more metal or nonmetal elements? Where are the nonmetals found on the periodic table?

There are more metal elements. The nonmetals are found on the top right of the periodic table

What is the difference between a monatomic and a diatomic gas? Give one example of each

A monatomic gas is a gas that is made up of single atoms example helium gas

A diatomic gas is made up of molecules that are formed by two atoms of the same element bonded together for example O2 = oxygen gas

b) Are most elements solid, liquid or gas at room temp? Give one example of each

Most elements are solids at room temp ex copper (Cu), only two are liquids ex bromine Br and a few are gases ex nitrogen N2

What is the difference between isotopes and ions? Give examples of each

Isotopes are two atoms of the same element (they have the same number of protons) that have different numbers of neutrons and therefore different masses . Examples = lithium with 3 p+ and 4 n and an atomic mass of 7 amu and lithium with 3 p+ and 3 n and an atomic mass of 6 amu.

Ions are charged particles that are formed when an atom gains or loses electrons. Examples N -3 or Mg +2