properties & changes

Chapter 9

Properties and Changes

Physical & Chemical PropertiesSec 9-1 H.W. pg 248 ques. 1-4

A physical property of something is one that you can detect with your senses.

Include color shape, size, texture All matter has physical properties. What

about your notebooks? What physical properties do you see?

One important property of all matter is density.

Density is the measure of the ratio of an objects mass to its volume.

Density An objects mass is the amount of space

that it takes up. And it is calculated by using a balance or scale.

The mass is given in grams. The volume is calculated by using the

equation l x w x h. This only works on objects that have perfectly straight lines though.

How would you find the volume of an object that doesn’t have straight lines. Like an ordinary rock?

Volume

With something like a rock we would have to use a graduated cylinder to see how much water the rock displaces, or moves.

So we fill up a cylinder with 10ml of water and then drop the rock in and see how much the water moved up. If it moved up to 12ml then the volume of the rock is 2ml.

Density continued

Now that we know that the vol. of the rock is 2 ml and lets say we know that the rock is 5 grams, we can use the density formula to determine the rocks density.

Density is: d=m/v or mass divided by volume.

So what is the density of our rock? D=m/v so d=5g/2ml and d=2.5g/ml

Density continued

We can use density to identify similar objects.

There is a mineral called pyrite that looks almost exactly like gold, however it is about 19x less dense then gold.

So if we wanted to find out if a rock we had was real gold or pyrite we could find the densities of the two.

We would find that the rock with the higher density would be gold.

Acids and Bases These 2 substances are very important to biology. They are characterized by using a pH scale. Every substance has a pH. This scale goes from 1-14 and according to wear

the a substance falls on this scale depends on if its an acid or a base.

An acid will appear on the scale between 1-6 and a base will be a number b/w 8-14

1 being a very strong acid and 14 being a very strong base.

A pH of 7 is considered to be neutral and is the pH of water.

Physical Properties of Acids and Bases

Some acids, like HCL or Sulfuric acid (H2So4), can severely burn you if you come into contact with them, But some acids that you come into contact with are harmless, like citrus acid.

A physical property of an acid would be that it tastes sour and has a low pH.

Bases have a high pH and taste bitter. Some common strong bases are household cleaners like ammonia.

Chemical properties

A chemical property is a characteristic of a substance that allows it to change into another substance.

An example of this is something's ability to light on fire, like gasoline or the phosphorus on a match.

Another is a substances ability to be toxic like venom from a snake or spider.

Another common one is the ability of iron to runt when it comes into contact with air.

Chemical Properties of Acids and Bases

Acids can corrode or eat away some metals. Acid in soda can eat away at car paint.

Bases react with fats, like the ones under your skin. If you spill a strong base on you like NaOH, it react with the fats and oils in you skin and burns you and basically turns the fat under your skin into soap.

Physical and Chemical Changes

A physical change is any change in size shape or form. The chemical composition of the substance doesn’t change.

An example is when matter changes states from solid, to liquid, to gas or vice versa.

When an ice cube melts it becomes liquid, and when the liquid is heated up it becomes steam.

All three state changes are physical because in all three states water remains water, it is not changed to a different substance.

So melting freezing and vaporizing are all physical properties.

Physical and Chemical Changes

A chemical change occurs when a substance’s chemical composition changes form and a new substance is formed.

An example is when iron reacts with air to form rust.

The iron is no longer iron it is now rust, a different, weaker chemical form of iron.

Another chemical change is when Na and Cl join in salt water to form a mineral called halite, or rock salt.