Matter and Chemical Reactions

Read each observation about water. 1. Water droplets attract one another and form a larger pool of water. 2. Water sticks to your hands after you wash them. 3. Water sticks to a spiderweb after a rainstorm. 4. Water from a fountain forms droplets. Choose the option that correctly identifies which observations are a result of cohesion and which observations are a result of adhesion.

• A. Cohesion: 1, 4; Adhesion: 2, 3

• B. Cohesion: 2, 3; Adhesion: 1, 4

• C. Cohesion: 1, 2, 3; Adhesion: 4

• D. Cohesion: 3, 4; Adhesion: 1, 2

A group of students finds two jars of chemicals that they label A and C. To help determine the contents, they conduct a pH test using pH paper and also test a jar of pure water to compare the results to. The results of the test are shown using the pH test paper in the image. Are the substances in jars A and C acids or bases? Select all that apply.

• Jar C is a base because it has a pH higher than pure water.

• Jar A is a base because it has a pH higher than pure water.

• Jar A is a base because it has a pH lower than pure water.

• Jar C is an acid because it has a pH lower than pure water.

• Jar A is an acid because it has a pH lower than pure water.

The pH of acids is _______________: than pure water while the pH of bases is _______________ than pure water. When a strong acid is added to pure water, the pH will change and become ________ than the pH of the pure water. When a strong base is added to pure water, the pH will change and become _______________ than the pH of the pure water.

• A. lower; higher; lower; higher

• B. lower; lower; higher; higher

• C. higher; lower; higher; lower

• D. higher; higher; lower; lower

A small needle floats on the surface of water. Soap, which separates water molecules, is added to the water. When soap is added to the water, the needle sinks. Which statement best explains what causes the small needle to sink?

• Soap increases the cohesion by decreasing the attraction between water molecules.

• Soap increases the cohesion by increasing the attraction between water molecules.

• Soap decreases the surface tension by increasing the attraction between water molecules.

• Soap decreases the surface tension by decreasing the attraction between water molecules.

Which phenomenon does not occur due to adhesion?

• Water droplets forming on a waterproof jacket

• A puddle of water evaporating at a slower rate

• Dew forming on a leaf in the early morning

• A wet, plastic tablecloth sticking to a table

Look at the model of the two balloons. Each balloon contains a different gas. The presence of two unidentified elements, element 1 and element 2, are labeled in the image. Which statements identify and explain the type of matter in each balloon? Select all that apply.

• Balloon A contains an element because there is only one type of atom.

• Balloon A contains a compound because there are two atoms bonded together.

• Balloon B contains a homogeneous mixture because there are two different types of atoms that are not chemically bonded and the mixture is uniform.

• Balloon B contains a heterogeneous mixture because there are two different compounds that are not chemically bonded and the mixture is not uniform.

• Balloon B contains an element and a compound because there are two types of atoms that are chemically bonded together.

Tags

NGSS.MS-PS1-1

A group of students observe an insect sitting on the surface of water. They discuss how surface tension, cohesion, and adhesion can explain this observation. They disagree on whether surface tension is caused by cohesion or adhesion. Which student has the best explanation?

• Destiny: “Cohesion makes water molecules push each other away, which makes the water very stable for insects to walk on. This is why cohesion causes surface tension.”

• Rosa: “The attraction between water molecules is what causes cohesion. Cohesion is the force that pushes up on the surface of the water to counteract the force of the insect.”

• Franklin: “Surface tension happens when water molecules stick to the insect. Water at the surface sticks to the insect, so surface tension is caused by adhesion.”

• Paolo: “Molecules at the surface have stronger cohesion with the molecules around them, so the surface acts like a thin film. This is why cohesion causes surface tension.”

Consider the data in the table. | Substance | Appearance | pH Value | |-----------|-------------------|----------| | 1 | Red liquid | 13 | | 2 | Clear liquid | 7.2 | | 3 | White/clear liquid| 5.7 | | 4 | Brown liquid | 6.2 | | 5 | Cloudy liquid | 12.4 | | Pure water| Clear liquid | 7 | Which of the substances are considered acids?

• A. 1 and 5, because the substances have a pH higher than 12

• B. 3 and 4, because the substances have a pH that is closest to pure water

• C. 5 and 2, because the substances have a pH that is higher than pure water

• D. 4 and 3, because the substances have a pH lower than pure water

Tags

NGSS.MS-PS1-2

Students are comparing models of homogeneous and heterogeneous mixtures. Which three descriptions accurately describe a model of a homogeneous mixture?

• The atoms in the model are all different sizes.

• The substances are evenly distributed throughout.

• There is more than one type of atom in the model.

• The substances are all chemically bonded to each other.

• The substances are not chemically bonded to each other.