Chemical Research Nine Weeks Exam

An element is a pure substance that contains only one type of atom. It cannot be broken down into simpler substances by chemical means. In contrast, a compound is a substance that is made up of two or more different types of atoms chemically combined. A mixture is a combination of two or more substances that are physically combined and can be separated by physical means. A solution is a type of mixture where one substance is dissolved in another. Therefore, the correct answer is c. element.

Protons have a positive electric charge. They are subatomic particles found in the nucleus of an atom and carry a positive charge equal in magnitude to the negative charge of an electron. Electrons, on the other hand, have a negative charge, while neutrons have no charge at all. Atoms, which consist of protons, neutrons, and electrons, have an overall neutral charge due to the equal number of protons and electrons.

Electrons form a cloud around the nucleus in an atom. Electrons are negatively charged particles that orbit the nucleus in specific energy levels or shells. These shells or energy levels can be thought of as the "cloud" around the nucleus. Electrons are responsible for the chemical properties of an atom as they participate in chemical reactions and bonding with other atoms.

A carbon atom has a mass number of 12, which refers to the total number of protons and neutrons in the nucleus. Since the atomic number of carbon is 6, indicating the number of protons, and the mass number is 12, we can deduce that the number of neutrons is also 6. Therefore, the correct answer is d. 6,6.

Oxygen usually exists as a gas on Earth. This is because the atmospheric conditions on Earth allow oxygen molecules to exist in a gaseous state. Oxygen gas is essential for supporting life as it is a crucial component of the air we breathe.

Hydrogen bonds occur because of the polar molecules of water. In a water molecule, the oxygen atom is slightly negative and the hydrogen atoms are slightly positive. This polarity allows the oxygen of one water molecule to attract the hydrogen of another water molecule, forming a hydrogen bond. These bonds are weaker than covalent or ionic bonds, but they play a crucial role in many biological processes, such as the cohesion of water molecules and the structure of DNA.

Ions are electrically charged particles because they have gained or lost electrons, resulting in a net positive or negative charge. Molecules, solutions, and isotopes do not inherently possess an electrical charge. A molecule is a group of atoms held together by chemical bonds, and while individual atoms within a molecule may be charged, the molecule as a whole is neutral. Solutions are mixtures of substances in which the solute particles are evenly distributed, but they do not carry a charge. Isotopes are variants of an element with different numbers of neutrons, but they do not have a charge.

The color of your clothes is a physical property because it can be observed and measured without changing the chemical composition of the clothes. It is a characteristic that can be perceived by our senses and does not involve any chemical reactions or transformations.

When the mass of an object increases while the volume stays the same, the density of the object changes. Density is defined as the mass of an object divided by its volume. As the mass increases and the volume remains constant, the density of the object will increase. This means that the object becomes more compact and heavier for a given volume. Therefore, the correct answer is c. density.

The density of an object is calculated by dividing its mass by its volume. In this case, the mass is given as 50 g and the volume is given as 5 cm3. Therefore, the density can be calculated as 50 g / 5 cm3 = 10 g/cm3.

The word "magnetic" best describes the type of materials that attract iron. Magnetic materials have the ability to generate a magnetic field, which attracts iron and other magnetic substances. This attraction is due to the alignment of the magnetic domains within the material, creating a force that pulls iron towards it. Chemical, mass, and physical do not accurately describe this specific property of attracting iron.

In a water wave, energy is carried from particle to particle. As the wave travels through the water, each particle of water oscillates back and forth, transferring energy to the neighboring particles. This transfer of energy allows the wave to propagate through the water. The speed of the wave, the height of the wave (amplitude), and the composition of the water (matter) do not get carried from particle to particle in a water wave.

The pitch of a sound wave is determined by its frequency. Frequency refers to the number of cycles or vibrations that occur in a given time period. Higher frequencies result in higher pitch sounds, while lower frequencies result in lower pitch sounds. Therefore, the correct answer is b. frequency.

The distance between adjacent wave compressions is referred to as one wavelength. Wavelength is defined as the distance between two consecutive points in a wave that are in phase, such as two consecutive compressions or two consecutive crests. It is measured in units of length, such as meters or centimeters. Therefore, option a is the correct answer as it accurately describes the distance between adjacent wave compressions.

Boron-12 is the correct answer because the atomic number of boron is 5, which means it has 5 protons. The atomic mass of boron-12 is 12, which includes both protons and neutrons. Since the atomic mass is 12 and the atomic number is 5, the number of neutrons can be calculated by subtracting the atomic number from the atomic mass, which gives us 7 neutrons.

Water does not change to hydrogen and oxygen when electricity passes through it. This statement is incorrect because water undergoes electrolysis when an electric current is passed through it, resulting in the formation of hydrogen gas at the cathode and oxygen gas at the anode. This is a chemical property of water rather than a physical property.

The volume of a rectangular prism can be calculated by multiplying its length, width, and height. In this case, the length is 20 cm, the width is 10 cm, and the height is 3 cm. Multiplying these values together (20 cm * 10 cm * 3 cm) gives us a volume of 600 cm3.

The ability to burn is an example of a chemical property because it involves a chemical reaction. Burning is a process that occurs when a substance reacts with oxygen to produce heat, light, and often new substances. This property is specific to certain substances and can be used to identify and classify them. In contrast, color, mass, and density are examples of physical properties, which do not involve a change in the chemical composition of a substance.

Water boiling is an example of a physical change because it involves a change in the state of matter from liquid to gas without altering the chemical composition of the water molecules. The water molecules are heated, gaining energy and moving faster, causing the bonds between them to break and form water vapor. This change is reversible, as the water vapor can be condensed back into liquid water by cooling.

During a physical change, the composition of the substance remains the same. This means that the molecules and atoms that make up the substance do not change or rearrange. Instead, only the physical properties of the substance, such as its shape, size, or state of matter, may change. The chemical bonds between the atoms remain intact, and no new substances are formed. Therefore, the correct answer is b. composition stays the same.

Bread being baked is an example of a chemical change because it involves a transformation of the bread's composition. During the baking process, the heat causes chemical reactions to occur, such as the Maillard reaction, which results in the browning of the bread and the formation of new compounds with different properties. This change is irreversible, as the bread cannot be transformed back into its original form.

A change in shape is not a clue that could indicate a chemical change because a chemical change refers to a transformation at the molecular level, where the composition of the substance changes. A change in shape, on the other hand, only refers to a physical change where the arrangement or position of the molecules may be altered, but the chemical composition remains the same.

During physical and chemical changes, the property that stays the same is mass. Mass is a measure of the amount of matter in an object and it remains constant regardless of the type of change that occurs. Physical changes involve a change in the state or form of matter, such as melting or boiling, but the total mass of the substance remains unchanged. Similarly, during chemical changes, where new substances are formed through chemical reactions, the total mass of the reactants is equal to the total mass of the products. Therefore, mass is a conserved property during both physical and chemical changes.

The lowest points on a transverse wave are called troughs. This is because a transverse wave consists of peaks and valleys, with the troughs being the lowest points or valleys. The crests, on the other hand, are the highest points or peaks of the wave. Compressions and rarefactions are terms used to describe the regions of high and low pressure in a longitudinal wave, not a transverse wave.

Mechanical waves require a medium to travel through. A medium refers to any substance or material that can transmit the wave energy. This can include solids, liquids, and gases. In the case of mechanical waves, such as sound waves or seismic waves, they rely on the particles of the medium to transfer the energy from one point to another. Without a medium, mechanical waves cannot propagate, which is why options a, b, and c are incorrect. Therefore, the correct answer is d. a medium.