Chemistry Mid Term Test

Rusting is classified as a chemical change because it involves a chemical reaction between iron, oxygen, and water. When iron comes into contact with oxygen and moisture, it undergoes oxidation, forming iron oxide (rust). This process is irreversible and results in a change in the chemical composition of the iron. Therefore, rusting is considered a chemical change rather than a physical change.

The correct answer is Mg. The symbol for magnesium is Mg.

A graduated cylinder is used to measure volume. It is a tall, narrow container with markings on the side that indicate different volume measurements. The markings allow for precise measurements of liquid volume. A thermometer measures temperature, a scale measures weight, and a ruler measures length, but none of these instruments are specifically designed to measure volume. Therefore, the correct instrument to measure volume is a graduated cylinder.

The correct answer is strontium. Strontium is an element with the symbol Sr on the periodic table. It is a soft, silver-white metal that is highly reactive and found in various minerals. Strontium is commonly used in the production of fireworks, as well as in the manufacturing of glass for cathode ray tubes.

The correct answer is solid, liquid, and gas. These are the three states of matter. Solids have a fixed shape and volume, liquids have a definite volume but take the shape of their container, and gases have neither a fixed shape nor volume. Protons, neutrons, and electrons are subatomic particles, not states of matter. Metals, non-metals, and metalloids are classifications of elements. Freezing, melting, and evaporation are physical processes that can occur in different states of matter.

A positive charge particle found in the nucleus is called a proton. Protons have a positive charge and are one of the fundamental particles that make up an atom. They are located in the nucleus along with neutrons, which have no charge. Electrons, on the other hand, have a negative charge and orbit around the nucleus. Therefore, the correct answer is proton.

The correct answer is Cu. Copper is a chemical element with the symbol Cu, derived from the Latin word "cuprum." It is a soft, malleable, and ductile metal that is widely used in electrical wiring, plumbing, and various industrial applications. The symbol Cu is internationally recognized and used to represent copper in the periodic table and chemical equations.

The mass number of an atom is the sum of the number of protons and neutrons in its nucleus. In this case, the atom contains 11 protons and 12 neutrons, so the mass number is 11 + 12 = 23.

A scale is used to measure mass. It is a device that uses the force of gravity to determine the weight of an object, which is directly proportional to its mass. By placing an object on a scale, it provides a numerical value that represents the mass of the object. Graduated cylinders, thermometers, and beakers are not used to measure mass, but rather to measure volume and temperature.

Burning wood is an example of a chemical change because it involves a chemical reaction. When wood is burned, it undergoes a combustion reaction where it reacts with oxygen in the air to produce heat, light, carbon dioxide, and water vapor. This reaction results in the formation of new substances with different properties than the original wood. Therefore, burning wood is not just a change in physical state or appearance, but a transformation at the molecular level, making it a chemical change.

Melting candle wax is classified as a physical change because it does not involve a change in the chemical composition of the substance. During melting, the wax changes from a solid to a liquid state due to the application of heat. However, the molecules of the wax remain the same, only their arrangement and movement change. This means that the properties of the wax, such as its molecular structure and composition, remain unchanged. Therefore, melting candle wax is considered a physical change.

The period in a sentence typically goes from left to right. This means that it starts at the left side of the sentence and moves towards the right side. This is the standard convention in English writing.

The electron in the outer shell of an atom is called a valence electron. Valence electrons are involved in the formation of chemical bonds and determine the reactivity and chemical properties of an element. They can be shared, transferred, or participate in bonding with other atoms. Therefore, the correct answer is "valence electron."

Elements form compounds in order to become stable like the noble gases. Noble gases have a full outer electron shell, which makes them very stable and unreactive. Other elements, which do not have a full outer electron shell, tend to react with other elements in order to gain, lose, or share electrons and achieve a stable electron configuration like the noble gases. This stability is achieved by forming chemical bonds with other elements, resulting in the formation of compounds.

The correct answer is "anything that have mass and occupy space." This definition accurately encompasses the concept of matter, which refers to anything that has both mass and occupies space. Matter can exist in various forms, including solid, liquid, or gas, and is composed of particles such as atoms and molecules. This definition captures the fundamental characteristics of matter and distinguishes it from other entities that do not possess mass or occupy space.

Water is composed of one atom of oxygen and two atoms of hydrogen. This is because the chemical formula for water is H2O, which means that there are two hydrogen atoms bonded to one oxygen atom.

Neon (Ne) is an example of a noble gas. Noble gases are a group of elements that are very stable and do not readily react with other elements. They have a full outer electron shell, which makes them chemically inert. Neon is commonly used in advertising signs and lighting due to its bright orange-red glow when electrically charged. It is also used in cryogenic applications and as a coolant in certain scientific equipment.

Br is an example of a halogen because it belongs to the halogen group on the periodic table. Halogens are a group of highly reactive nonmetals that have seven valence electrons, making them one electron short of a full outer shell. They readily react with other elements to achieve a stable electron configuration. Br, also known as bromine, is a reddish-brown liquid at room temperature and is commonly used in disinfectants, flame retardants, and pharmaceuticals.

because of increase in nuclear charge

Neutrons have a neutral charge. Unlike protons, which have a positive charge, and electrons, which have a negative charge, neutrons do not possess any charge. This means that they are not attracted to or repelled by electric fields and do not contribute to the overall charge of an atom. Neutrons are found in the nucleus of an atom along with protons, and their neutral charge helps to balance out the positive charge of the protons, keeping the atom stable.

Water is an example of a compound because it is made up of two different elements, hydrogen and oxygen, chemically bonded together. In a compound, the elements combine in a fixed ratio and can only be separated by a chemical reaction. Water, with the chemical formula H2O, fits this description as it always contains two hydrogen atoms and one oxygen atom.

Electrons are located in shells within an atom. Shells are specific energy levels or orbitals where electrons can be found. These shells are arranged in increasing energy levels, with the innermost shell having the lowest energy and the outermost shell having the highest energy. Each shell can hold a specific number of electrons, with the first shell holding a maximum of 2 electrons, the second shell holding a maximum of 8 electrons, and so on. The arrangement of electrons in these shells determines the chemical properties and reactivity of an atom.

To convert milliliters to liters, you divide the given value by 1000. In this case, 23 milliliters divided by 1000 equals 0.023 liters. Therefore, the correct answer is 0.023L.

A heterogeneous mixture is a mixture that contains two or more visibly distinguishable phases or components. In this case, the mixture separates into two visible phases, indicating that it is not uniform throughout and therefore classified as a heterogeneous mixture.

To measure density, we need to determine the mass and volume of an object. A graduated cylinder is used to measure the volume of a liquid or irregularly shaped solid. A scale is used to measure the mass of the object. Therefore, the correct answer is graduated cylinder and scale. A thermometer and stop watch are not used to measure density, and a ruler alone cannot accurately measure the volume of irregularly shaped objects.

Covalent compounds are formed by sharing electrons. In a covalent bond, two atoms share one or more pairs of electrons in order to achieve a stable electron configuration. This sharing of electrons allows both atoms to fill their outermost electron shells and form a strong bond between them. This type of bonding is typically found between nonmetals and results in the formation of molecules.

The SI unit used to measure volume is liters. Volume is a measure of the amount of space occupied by an object or substance, and liters is the standard unit for measuring volume in the International System of Units (SI). It is commonly used to measure the volume of liquids and gases. Grams is a unit of mass, kilometer is a unit of length, and degrees Celsius is a unit of temperature, none of which are used to measure volume.

A substance consisting of two elements chemically combined is known as a compound. In a compound, the elements are bonded together in a fixed ratio and cannot be separated by physical means. Unlike mixtures, where the components can be present in varying proportions, compounds have specific chemical properties and formulas. Therefore, compound is the correct answer in this case.

A change from liquid to solid is called freezing. Freezing occurs when the temperature of a substance is lowered below its freezing point, causing the molecules to slow down and arrange themselves into a solid structure. This process involves the release of heat energy. Melting, on the other hand, is the change from solid to liquid, while boiling refers to the change from liquid to gas. Condensation is the change from gas to liquid.

Condensation is the process in which a substance changes from its gaseous state to its liquid state. This occurs when the temperature of the gas decreases, causing the particles to lose energy and come closer together, forming a liquid. Sublimation refers to the change from solid to gas without passing through the liquid state, evaporation is the process of a liquid turning into a gas, and freezing is the transformation from liquid to solid. Therefore, condensation is the correct answer for a change from gas to liquid.

Breaking a class is classified as a physical change because it does not involve a change in the chemical composition of the material. The glass is still made up of the same molecules before and after it is broken. Only the physical arrangement of the molecules has changed. This is different from a chemical change, where new substances are formed with different chemical properties.

The correct answer is "packed together and can only vibrate". In a solid, the molecules are tightly packed together and held in a fixed position by strong intermolecular forces. This arrangement restricts their movement to only vibrating in their positions. The molecules do not have the freedom to slide over each other or move from one place to another, as described in the other options.

The atomic number of an element represents the number of protons in the nucleus of an atom. This number determines the element's identity and its position on the periodic table. The other options, such as the number of neutrons, atomic mass, and mass number, are not equivalent to the atomic number and do not define the element. Therefore, the correct answer is the number of protons.

To calculate the atomic mass, we need to consider both protons and neutrons. Protons have a positive charge and are found in the nucleus of an atom, while neutrons have no charge and are also located in the nucleus. Electrons, on the other hand, have a negative charge and are found in the electron cloud surrounding the nucleus. Since electrons have a negligible mass compared to protons and neutrons, they are not included in the calculation of atomic mass. Therefore, the correct answer is to sum up the numbers of protons and neutrons.

Xe, also known as xenon, is a noble gas. Noble gases have a full outer electron shell, making them stable and unreactive. They rarely participate in bonding because they already have a stable electron configuration. Therefore, Xe is the element that is least likely to participate in bonding compared to Si, Sr, and K.

Chlorine is not a compound because it is an element found on the periodic table. Compounds are formed when two or more elements chemically combine, but chlorine exists as a pure element and does not need to combine with other elements to form a compound. On the other hand, sugar, water, and carbon dioxide are all compounds because they are made up of multiple elements chemically bonded together.

The correct answer is "vertical columns" because in the periodic table, elements are arranged in columns called groups or families. Elements within the same group have similar chemical properties and the same number of valence electrons. These groups or families are arranged vertically, making the vertical columns the correct description for a group or family in the periodic table.

A metalloid is an element that exhibits properties of both metals and nonmetals. It has characteristics of metals, such as being able to conduct electricity and heat, but also has nonmetallic properties, such as being brittle and having low melting points. Metalloids are found along the zigzag line on the periodic table, separating the metals from the nonmetals. Therefore, a metalloid is the correct answer for an element with both metallic and nonmetallic properties.

When matter is heated, the molecules gain energy and start moving faster. This increased kinetic energy causes the molecules to move farther apart from each other. As the temperature rises, the intermolecular forces weaken, allowing the molecules to spread out more, leading to an expansion of the substance. This phenomenon is observed in various states of matter, such as solids turning into liquids or liquids turning into gases when heated.

To convert centimeters to millimeters, you need to multiply the value in centimeters by 10. In this case, 23.6 cm multiplied by 10 equals 236 mm. Therefore, the correct answer is 236mm.

Elements across a period have the same number of shells. This is because as you move across a period from left to right on the periodic table, the number of electrons in the outermost energy level (valence electrons) remains the same, while the number of protons and atomic mass generally increase. The number of shells determines the energy level of the electrons and is responsible for the element's chemical properties.

Covalent compounds have lower melting and boiling points compared to ionic compounds. This is because covalent compounds consist of molecules held together by weak intermolecular forces, such as London dispersion forces or dipole-dipole interactions. These forces are relatively weak and can be easily overcome, resulting in lower melting and boiling points. On the other hand, ionic compounds have strong electrostatic attractions between positively and negatively charged ions, which require a significant amount of energy to break, leading to higher melting and boiling points.

Sulfur belongs to group 16 on the periodic table, also known as the chalcogens. Group 16 elements are characterized by having 6 valence electrons and include oxygen, sulfur, selenium, tellurium, and polonium. These elements have similar chemical properties and tend to form compounds with other elements by gaining or sharing electrons to complete their outer electron shell. Sulfur, in particular, is a nonmetal and is commonly found in various minerals and compounds, playing important roles in biological processes and industrial applications.

Na and Ca belong in the same group because they are both alkali earth metals. Si and Al do not belong in the same group because Si is a metalloid while Al is a metal. C and Ge belong in the same group because they are both nonmetals. S and Cl belong in the same group because they are both nonmetals and halogens.

Evaporation is the correct answer because it refers to the process of a liquid changing into a gas. This occurs when the molecules of a liquid gain enough energy to escape from the surface and become vapor. Evaporation commonly happens at the boiling point of a substance, but it can also occur at lower temperatures.

Baking a cake is classified as a chemical change because it involves a chemical reaction. During the baking process, the ingredients in the cake batter undergo a series of chemical reactions, such as the leavening agents reacting with heat to produce carbon dioxide gas, causing the cake to rise. Additionally, the proteins in the flour coagulate, the sugars caramelize, and the fats melt and combine with other ingredients to form a new substance with different properties than the original batter. These chemical reactions result in the formation of a cake, which is a completely different product from the original ingredients.

Scandium is an example of a transition element because it is a d-block element that has partially filled d orbitals. Transition elements are characterized by their ability to form multiple oxidation states and exhibit a wide range of chemical reactivity. Scandium, with its atomic number 21, belongs to the transition metal series and possesses properties typical of transition elements such as high melting and boiling points, metallic luster, and the ability to form colored compounds.

The correct answer is K because K represents the chemical symbol for potassium, which is an alkali metal. Alkali metals are found in Group 1 of the periodic table and are highly reactive. They have one valence electron and are known for their ability to easily lose this electron to form positive ions. Potassium is a soft, silvery-white metal that reacts violently with water. It is commonly found in nature and is an essential element for many biological processes.

The octet rule states that elements become stable by having 8 valence electrons. This means that atoms tend to gain, lose, or share electrons in order to achieve a full outer shell with 8 electrons, similar to the noble gases. By doing so, they achieve a more stable electron configuration, which is energetically favorable. This rule helps to explain the formation of chemical bonds and the stability of different elements and compounds.

To convert grams to kilograms, we divide the given value by 1000 since there are 1000 grams in a kilogram. Therefore, 20 grams is equal to 0.020 kilograms.