Class 3 Blog

Properties of Water

Water molecule consists of one oxygen atom and two hydrogen atoms. Since two pairs of electrons are unshared, there are two lone pairs surrounding the oxygen atom in the center. One water molecule can bond with four others because each hydrogen bonds with another oxygen atom and the oxygen can bond with two hydrogen atoms. These bonds are called hydrogen bonds.

Properties

Ability to moderate temperature—The temperature of water rises and water can evaporate due to increase in molecular motion. When the water mixes with air, the water cools off the air and thus the temperature of air will decrease. When the land is colder, the water molecules that evaporate from the ocean have more molecular motion and thus increase the temperature of air.

Cohesion and Adhesion

Cohesion: Similar molecules can stick with each other due to mutual attraction.

Adhesion: Different molecules or surfaces can stick with each other.

Water in plants

Due to adhesion, water in the roots adheres to the inner tube. Due to cohesion, the water molecules stick together and go up against the force of gravity from the roots to the leaves.

Class 2 Blog

Basic Chemistry

In the class, we reviewed basic concepts of elements, compounds, and bonds between atoms.

Atomic number = number of protons = number of electrons

Atomic mass number = number of protons + number of neutrons

Difference between an element and a compound: Both are pure substances. An element is made of same type of atoms, whereas a compound is made of different elements in definite proportions.

Isotopes of an element have different number of neutrons. Some isotopes are very useful in chemical and biological research: Carbon dating uses the decay of Carbon-14 to estimate the age of organic materials and Calcium-47 helps researchers study the cellular functions and bone formation in mammals.

Ionic Bond: Atoms transfer valence electrons to form an ionic bond between them.

Covalent Bond: Atoms share valence electrons to form a covalent bond between them.

These two bond formations can be illustrated through Lewis Dot Structure.

Strong covalent bonds and weak bonds are both important because strong covalent bonds link atoms to form a cell's molecules and weak bonds can be broken down and can be made again easily.

Milk and Food Coloring Lab 8/22

Why does the milk interact with food coloring?

Hypothesis: The milk interacts with food coloring mainly because of the soap. Since there is fat and protein in milk, soap can bond with these molecules and form new chemicals.

Procedure

1.     Measure 10mL of the testing liquid with a graduated cylinder

2.     Pour the liquid into a pan

3.     Add 1-2 drops of red and blue food coloring in the liquid

4.     Add 1 drop of dish soap in the liquid

5.     Repeat steps 1-4 with different liquids

Materials used: Whole milk, skim milk, orange juice, coffee, water, Palmolive dish soap, food coloring (red & blue), stop watch, graduated cylinder, toothpicks, pan

First Experiment

Dependent variables: Interaction between liquid and food coloring

Independent variables: Liquid

Control variables: Food coloring, dish soap, the amount of liquid

In the first experiment, we used whole milk, skim milk, orange juice, coffee, and water to test the liquids’ reaction with food coloring after the addition of dish soap. We observed that whole milk, skim milk, orange juice and coffee created spirals with food coloring. Only water didn’t generate such reaction with food coloring.

Whole Milk vs. Skim Milk

Orange Juice vs. Coffee

Water

Second Experiment:

Dependent variables: Diffusion of food coloring

Independent variables: Liquid

Control variables: Time, food coloring, dish soap, the amount of liquid

Procedure

1.     Measure 10mL of the testing liquid with a graduated cylinder

2.     Pour the liquid into a pan

3.     Add 1-2 drops of red and blue food coloring in the liquid

4.     Repeat Step 1-3 with different liquids

In the second experiment, we paired up whole milk with skim milk, and orange juice with coffee. For each pair, we used stopwatch to observe the change of the food coloring with the liquid in one minute. As a result, the food coloring dissolved faster in whole milk and orange juice without the addition of dish soap.

Whole Milk vs. Skim Milk

Orange Juice vs. Coffee

Conclusion: Since the dish soap is controlled, the liquids would cause the difference in reactions. In this dish soap, there is a chemical known as degreaser or surfactant. The surfactant helps lower surface tension in bonding between both polar molecules and nonpolar molecules. With this chemical, fats and proteins are allowed to move freely, thereby creating spirals with the food coloring. In addition, we know that there is more fat and protein in whole milk than in skim milk. And the food coloring spread faster in whole milk than in skim milk. Therefore, we made our conclusion that the more fat a liquid has, the faster the food coloring can spread.