8th grade blog answers

Week 1:
1.Describe the difference between physical and chemical changes in terms of what happens to matter involved in each kind of change. Use examples to help with your explanation.

First of all, when physical change occurs in a substance, you will not be able to create a new substance. The substance will remain in its original state. In contrast, when chemical change occurs in the substance, you will be able to produce a different kind of substance. This means you will lose the original substance and a new one will form.
Based on this premise, any physical change that occurs in matter or substance is completely reversible. But when a chemical change happens, you will not be able to reverse or undo the transformation. For example, water can freeze so liquid can turn to solid but the substance is still water. You can unfreeze ice to revert to the liquid state of water. But if you burn paper, you will get a new substance called ash. You cannot ‘un-burn’ ash to transform it back to paper.
Another big difference between physical and chemical change is the speed of transformation. Physical change occurs faster and sometimes instantaneously. Most chemical changes, on the other hand, take longer time to become discernible. You can crumple a tin can and you will immediately see physical changes. But corrosion of tin can occurs very slowly; it will take a long time before you see the appearance of rust on the can.
There is a wide difference between physical and chemical changes. With physical change, you are not transforming the original molecular composition of the substance. But with chemical change, the molecular structure is being transformed thus you will get a new substance.
Resource: http://www.differencebetween.net/science/difference-between-physical-and-chemical-change/

2. The Statue of Liberty was originally a copper color. After being exposed to air, she turned a greenish color. What kind of change happened? 


The Statue of Liberty is made of copper and you may have seen bluish or greenish tints to your pennies that have been left out to oxidize. Oxidation occurs as a chemical process happens that allows oxygen to slowly deteriorate metals and various other materials. Copper oxide is the product that actually is green when you see green copper pennies and subsequently the Statue of Liberty in the waters of the Atlantic Ocean near New York. The Statue of Liberty is naturally green because of this chemical process and as such needs to be maintained regularly to ensure that it does not erode over time.
Copper is amazing in the fact that it usually will not erode so much when oxidized. The oxidation on the outside actually protects the copper inside by stopping further erosion. The original reason why the Statue of Liberty turned green is because of the heavy saline waters that actually accelerate the oxidation process on metals. The many misty sprays of the ocean caused the copper to turn green from exposure and many people see the green statue as beautiful anyways.
Resource:http://www.whyisthestatueoflibertygreen.com/why-is-the-statue-of-liberty-green.html

3. Keisha fills a balloon with helium while inside a heated building. She then takes the balloon outside on a cold winter day. The air pressure is the same inside and outside. Predict what will happen to the balloon, and explain your answer.
If the pressure on a gas is increased, the volume of a gas decreases. Also, the volume of the gas is directly proportional to the absolute temperature. If you heat the gas, it expands; if you cool it, its volume decreases.

Heating the balloon makes the helium atoms move faster. The force of their collisions with the wall of the balloon increases. The increased force is an increase in pressure which, in turn, stretches the rubber and makes the balloon expand. Cooling does the opposite. When the balloon cools, the pressure inside drops, then the elasticity of the rubber shrinks the internal volume, and the overall volume of the balloon gets smaller. As a result, it displaces less air and therefore loses some of its lifting capacity.

Resource: http://www.newton.dep.anl.gov/askasci/phy00/phy00642.htm

Week 2:
1. The volume of a substance in a gaseous state is 1,000 times the volume in a liquid state. How much space would 18mL of water take up if it evaporated? 

The volume of a substance in a gaseous state is 1,000 times the volume of the same substance in a liquid state. Therefore, to find the volume of a gas you would multiply 18ml X 1000. The answer is 18000mL of 18 Liters. The liquid molecules up take up less space because the molecules are closer together and moving slowly compared to a gas whose particles move more freely.

2. Describe how the physical properties of solids, liquids and gases affect how each state of matter behaves when placed into a new container.
The primary physical characteristics of the various states of matter are the volume and shape of the material. They are what really define the state. Other characteristics—such as color—may be different in the various states of matter, but they do not define the state as do volume and shape. Gravity has an effect on the shape of liquids and gases.
The solid state of matter is when the material has a definite volume or size and distinct shape at a given temperature. At room temperature, a piece of iron at has a shape and size that does not change. Ice is another solid, but its temperature must be below 0o C (32o F). Most solid materials expand with increasing temperatures, but they retain their shape. A liquid has a definite volume, but it takes the shape of its container with the help of gravity. For example, if you pour water into a cup or container, it will take the shape of that container. If you put water in a balloon, the water will take the shape of the balloon, no matter how you change the shape of the balloon. On the other hand, in outer space, where there is no gravity such as in the Space Shuttle, water might float out of its container. Its shape will vary, but its volume will remain constant if the air pressure and temperature are constant.
Most liquids expand with an increase of temperature and constant air pressure.
The volume of a quantity of gas is dependent on its temperature and the surrounding pressure. If affected by gravity, it will take the shape of its container, but much of it will also spread out into the surrounding area.
Assuming little or no convection or circulation, a heavier gas will settle to the bottom. For example, carbon dioxide gas (CO2) is heavier than air.
The primary physical characteristics of the various states of matter are the volume and shape of the material, which influences the how each state of matter, behaves in a new container.

Resources: http://www.school-for-champions.com/science/matter_states.htm
3. Write a procedure for separating a mixture of ice, iron filings, and sawdust.
In this lab you will use several separation techniques to separate the components of a homogeneous mixture of solids. A magnet will be used to remove iron. Since the iron is the only metal, the magnet will attract only the iron and it will leave the sawdust and ice. Then hot water will be used to melt the ice (or you can just heat the mixture to melt the ice) and separate it from the sawdust since ice will melt in water but sawdust will not. Finally, the sawdust can be filtered out so that the remaining water is left. Using a magnet, heat and a filter is one way that this mixture can be separated.

Resource:
http://answers.yahoo.com/question/index?qid=20090929074619AAMVEN8Week

3:Why don't the noble gases in Group 18 on the periodic table form chemical bonds?
The noble gases are located in Group VIII of the periodic table. Helium and neon are examples of noble gases. These elements are used to make lighted signs, refrigerants, and lasers. The noble gases are not reactive. This is because they have little tendency to gain or lose electrons since their valence shell is filled.
http://chemistry.about.com/library/blperiodictable.htm

Week 5:

1.Jennifer placed 1.0 g of salt into one beaker, 1.0 g of soil into a second beaker, and 1.0 g of sugar into a third beaker. She then added 200mL of water to each beaker and stirred the contents for 3 minutes. Explain what Jennifer created and why. 


When two substances are combined in such a way that they do not react chemically, then this combination is called a mixture. There are two types of mixtures that are homogeneous and heterogeneous mixture. If the two substances cannot separate in a mixture, then the mixture is called homogeneous mixture. On the other hand, in a heterogeneous mixture one substance is suspended in the other substance. Two components of a heterogeneous mixture can be separated by applying some methods. Jennifer's combination of the soil and the water is a heterogeneous mixture because soil is not blended completely with water. Jennifer's mixture of salt and water is a homogeneous mixture (solution) because both the salt and the water retain their individual properties and the solution can be separated out. Jennfier's mixutre of sugar dissolves and is spread throughout the water. The sugar-water would be considered a homogeneous solution.

http://www.blurtit.com/q681870.html

http://wiki.answers.com/Q/Why_is_saltwater_a_mixture

http://www.chem4kids.com/files/matter_solution.html
2. The atomic mass of an element and the mass number of an atom of that element often have similar values. However, atomic mass and mass number are not the same. Explain the difference.

Atomic mass is the average of the masses of the existing isotopes in an element, but the mass number is the sum of the protons and neutrons in the nucleus of an atom. The mass number should not be confused with the relative atomic mass (also called atomic weight) of an element, which is the average atomic mass number of the different isotopes of that element, weighted by abundance.[5] For instance, there are two main isotopes of chlorine: chlorine-35 and chlorine-37. In any given sample of chlorine that has not been subject to mass separation there will be roughly 75% of chlorine atoms which are chlorine-35 and only 25% of chlorine atoms which are chlorine-37. This gives chlorine a relative atomic mass of 35.5 (actually 35.4527 g/mol).

Resources: http://en.wikipedia.org/wiki/Mass_number

3. The elements in the periodic table can be classified into metals, nonmetals, and metalloids. Describe the properties of these classes, and explain where the elements that fall into these classes can be found on the periodic table.

The elements in the periodic table can be classified into three groups based on their physical properties; metals, nonmetals and metalloids.
The metals are the largest group of elements. They are; all solids (except mercury); have a lustrous (shiny) appearance; are malleable and ductile; are good conductors of heat and electricity.
The next largest group is the nonmetals. The nonmetals; are found in gas, liquid or solid state; lack the remaining properties of the metals, i.e. are not malleable or ductile and are generally poor conductors (graphite is a very good electrical conductor).
The metalloids are a small collection of elements that lie between the metals and the nonmetals in the periodic table and share some of the properties of metals and nonmetals.
Resource: http://intro.chem.okstate.edu/1314F00/Lecture/Chapter2/Lec83000.html